The wound healing response within corneal epithelium cells is controlled by the purinergic P2X7 receptor, purinergic P2Y2 receptor, and Pannexin1 transmembrane proteins. The response is initiated by the release of ATP into the extracellular space by damaged cells and by the Pannexin1 channel protein and limited by the hydrolysis of extracellular ATP by ecto-ATPases. P2X7 and P2Y2 receptors are necessary for the initiation of cell migration, actin reorganization, and cell to cell communication required for the sheet like migration found within the corneal epithelium wound response. ARL 67156 Trisodium Salt Hydrate, an inhibitor for human and murine ecto-ATPases, was used to inhibit the hydrolysis of extracellular ATP during the wound response to prolong and further elevate extracellular ATP concentrations to increase the cellular activity and cell to cell communication of the wound response. The goal was to compare primary diabetic murine and human cells. However, there were issues with culturing these cells and diabetic murine and non-diabetic primary and established human cells were used for these experiments. Significant increases in cellular activity were found in both primary human cells with a 100 ARL to 10 ATP concentration ratio while no significant changes in cellular activity were found with the murine diabetic cells at any ARL concentration. In summary, with increased ATP in the wound response due to the inhibition of hydrolysis enzymes, human cells displayed increased levels and rates of cell-to-cell communication during the delayed wound response. / 2024-01-27T00:00:00Z

A sinalização purinérgica tem sido demonstrada como um um importante modulador dediversos processos fisiológicos e fisiopatológicos. Dentre os receptores purinérgicos, o receptor P2X7 distingui-se por requerir altas concentrações de ATP em sua ativação. As demonstrações prévias de que a glândula pineal responde a diferentes estímulos purinérgicose a altas concentrações de ATP sugere um papel para os receptores P2X7 nesta glândula, embora sua expressão e função não estivesse estabelecida. O objetivo deste trabalho, portanto, foi caracterizar funcionalmente o receptor P2X7 na glândula pineal de ratos. Os resultados obtidos demonstram, pela primeira vez, a expressão gênica e proteica do receptor P2X7 na glândula pineal. Os efeitos da ativação destes receptores levam a uma inibição nos níveis de melatonina induzida por isoprenalina por um mecanismo independente da via do fator de transcrição NF-kB e da fosfolipase C. Além disso, a estimulação destes receptores inibiu a síntese de TNF induzida por LPS, resultado este semelhante ao observado na presença do pré-tratamento com antagonistas do receptor P2X7. Estes dados confirmam a presença de receptores P2X7 na glândula pineal e reiteram o relevante papel da estimulação purinérgica a sobre a síntese de melatonina e sobre a capacidade da pineal em responder a PAMPs, como o LPS / Purinergic signalling has been demonstrated as an important modulator ofseveral physiological and pathophysiological processes. Among the purinergic receptors, the activation of P2X7 receptor requireshigh concentrations of ATP. The previous demonstration that the pineal gland is responsive to different purinergic stimulus and to high concentrations of ATPsuggests a role for P2X7, although its expression and function remained unclear. The aim of this study was to functionally characterize the P2X7 receptor in the rat pineal gland.The data showedthe P2X7 receptor mRNA and protein expression in the pineal gland. The effect of its activation leads toan inhibition of melatonin content induced by isoprenaline through an independent NF-kB and PLC pathways. Furthermore, the P2X7 receptor activation inhibits the LPS-induced TNF synthesis, a similar result observed in the presence of the pre-treatment with P2X7 receptors antagonists. These data demonstrate the presence of P2X7 receptors in the rat pineal gland and confirm the relevant role of the purinergic stimulation to the pineal melatonin synthesis and responsiveness to PAMPs such as LPS

L’ATP extracellulaire, à travers l’activation du récepteur P2X7, joue un rôle important dans l’immunité inné comme signal de danger responsable de l’assemblage de l’inflammasome, de la migration des cellules immunitaires et de la mort cellulaire. Bien que le rôle de la voie ATP/P2X7 dans l’immunité adaptative reste sous-estimé, il a été rapporté que le récepteur P2X7 participe aux mécanismes de signalisation impliqués dans l’activation des lymphocytes T, leur prolifération et leur différentiation. Notre laboratoire a récemment montré que les lymphocytes T effecteurs (CD4+ ou CD8+) en fin de réponse immunitaire secondaire, exprimant à la membrane la tyrosine phosphatase de membrane B220, sont totalement résistant à l’activation du récepteur P2X7 à cause d’une perte d’adressage de ce récepteur à la membrane. Le but de ce travail de thèse est d’étudier la sensibilité des lymphocytes T, à différents stades d’activation, aux activités cellulaires induites par l’ATP, notamment le clivage de la molécule de homing CD62L ou L-sélectine, l’ouverture du canal ionique, la formation du pore et l’externalisation de la PS. Mes principaux résultats montrent que les activités cellulaires dépendantes du récepteur P2X7 sont dissociées. Les lymphocytes T au stade effecteur/mémoire sont moins sensibles au clivage de la molécule CD62L que les lymphocytes T au stade naïf et récemment activé. Les lymphocytes naïfs T récemment activé en réponse immunitaire primaire sont les plus sensibles à la formation du pore. De plus, les lymphocytes T récemment activés, aussi bien en réponse immunitaire primaire que secondaire, sont les plus sensibles à l’externalisation de la PS. Enfin, dans les lymphocytes T récemment activé, les activités de pore et d’externalisation de PS, mais pas le clivage de CD62L, sont dépendantes du taux de calcium. / Extracellular ATP through the receptor P2X7 (P2X7R) plays a key role in innate immunity as a danger signal that causes the activation of the inflammasome, enhancement of immune cell migration and cell death. Although the role of the ATP/P2X7R pathway in adaptative immunity remains underestimated, it has been reported that P2X7R regulates signaling events involved in T-cell activation, proliferation, and differentiation into effector lineages. Moreover, we have previously shown that effector T lymphocytes (either CD4+ or CD8+) that express the B220 isoform of CD45 at the plasma membrane at the end of the secondary immune response are totally resistant to ATP stimulation due to loss of P2X7R membrane expression. In the present study, we compared the sensitivity of T lymphocytes to cellular activities trigerred by P2X7R according to their stage of activation. Interestingly, our results showed that P2X7-dependent cellular activities are dissociated. T lymphocytes at effector/memory stage are less sensitive to CD62L shedding than naïve or recently activated T lymphocyte during primary immune response. Naive T lymphocytes recently activated during primary immune response are the most sensitive to pore formation. Furthermore, recently activated T lymphocytes at both primary and secondary immune responses are the most sensitive to PS externalization. Finally, pore formation, PS externalization but not CD62L shedding, are dependent on calcium signaling.

P2X7-Rezeptoren stellen Schlüsselmoleküle bei der Entstehung und Aufrechterhaltung proinflammatorischer Zustände, chronischer Schmerzen sowie der neuroglialen Kommunikation dar. Ihre Aktivität wird durch eine Vielzahl zellbiologischer Mechanismen beeinflusst. Dazu gehört die allosterische Modulation durch extrazelluläre niedermolekulare Stoffe. Die Entwicklung selektiver und potenter P2X7-Modulatoren ist darum Gegenstand intensiver Forschung. Bisher sind jedoch keine Pharmaka für die klinische Anwendung verfügbar. Die Untersuchung zugelassener pharmakologischer Substanzen in einem akademischen Screening erbrachte eine hohe Trefferrate für P2X7-Rezeptoren. In dieser Arbeit wird die P2X7-Wirkung einiger der potentesten allosterischen Modulatoren genauer charakterisiert. Das Antihistaminikum Clemastin stellt dabei einen positiven allosterischen Modulator dar, der den Rezeptor gegenüber niedrigeren ATP-Konzentrationen sensibilisiert. Ivermectin, ein häufig angewendetes Anthelminthikum, konnte als potenzierender Modulator des humanen P2X7-Rezeptors charakterisiert werden. Mit den Phenothiazinen Prochlorperazin und Trifluoperazin zeigen sich schließlich ZNS-gängige Inhibitoren der ATP-induzierten P2X7-Aktivität, die für weiterführende in vivo-Untersuchungen hilfreiche pharmakologische Werkzeuge darstellen können.

A sinalização purinérgica tem sido demonstrada como um um importante modulador dediversos processos fisiológicos e fisiopatológicos. Dentre os receptores purinérgicos, o receptor P2X7 distingui-se por requerir altas concentrações de ATP em sua ativação. As demonstrações prévias de que a glândula pineal responde a diferentes estímulos purinérgicose a altas concentrações de ATP sugere um papel para os receptores P2X7 nesta glândula, embora sua expressão e função não estivesse estabelecida. O objetivo deste trabalho, portanto, foi caracterizar funcionalmente o receptor P2X7 na glândula pineal de ratos. Os resultados obtidos demonstram, pela primeira vez, a expressão gênica e proteica do receptor P2X7 na glândula pineal. Os efeitos da ativação destes receptores levam a uma inibição nos níveis de melatonina induzida por isoprenalina por um mecanismo independente da via do fator de transcrição NF-kB e da fosfolipase C. Além disso, a estimulação destes receptores inibiu a síntese de TNF induzida por LPS, resultado este semelhante ao observado na presença do pré-tratamento com antagonistas do receptor P2X7. Estes dados confirmam a presença de receptores P2X7 na glândula pineal e reiteram o relevante papel da estimulação purinérgica a sobre a síntese de melatonina e sobre a capacidade da pineal em responder a PAMPs, como o LPS / Purinergic signalling has been demonstrated as an important modulator ofseveral physiological and pathophysiological processes. Among the purinergic receptors, the activation of P2X7 receptor requireshigh concentrations of ATP. The previous demonstration that the pineal gland is responsive to different purinergic stimulus and to high concentrations of ATPsuggests a role for P2X7, although its expression and function remained unclear. The aim of this study was to functionally characterize the P2X7 receptor in the rat pineal gland.The data showedthe P2X7 receptor mRNA and protein expression in the pineal gland. The effect of its activation leads toan inhibition of melatonin content induced by isoprenaline through an independent NF-kB and PLC pathways. Furthermore, the P2X7 receptor activation inhibits the LPS-induced TNF synthesis, a similar result observed in the presence of the pre-treatment with P2X7 receptors antagonists. These data demonstrate the presence of P2X7 receptors in the rat pineal gland and confirm the relevant role of the purinergic stimulation to the pineal melatonin synthesis and responsiveness to PAMPs such as LPS

P2X7-Rezeptoren stellen Schlüsselmoleküle bei der Entstehung und Aufrechterhaltung proinflammatorischer Zustände, chronischer Schmerzen sowie der neuroglialen Kommunikation dar. Ihre Aktivität wird durch eine Vielzahl zellbiologischer Mechanismen beeinflusst. Dazu gehört die allosterische Modulation durch extrazelluläre niedermolekulare Stoffe. Die Entwicklung selektiver und potenter P2X7-Modulatoren ist darum Gegenstand intensiver Forschung. Bisher sind jedoch keine Pharmaka für die klinische Anwendung verfügbar. Die Untersuchung zugelassener pharmakologischer Substanzen in einem akademischen Screening erbrachte eine hohe Trefferrate für P2X7-Rezeptoren. In dieser Arbeit wird die P2X7-Wirkung einiger der potentesten allosterischen Modulatoren genauer charakterisiert. Das Antihistaminikum Clemastin stellt dabei einen positiven allosterischen Modulator dar, der den Rezeptor gegenüber niedrigeren ATP-Konzentrationen sensibilisiert. Ivermectin, ein häufig angewendetes Anthelminthikum, konnte als potenzierender Modulator des humanen P2X7-Rezeptors charakterisiert werden. Mit den Phenothiazinen Prochlorperazin und Trifluoperazin zeigen sich schließlich ZNS-gängige Inhibitoren der ATP-induzierten P2X7-Aktivität, die für weiterführende in vivo-Untersuchungen hilfreiche pharmakologische Werkzeuge darstellen können.:1. Bibliographische Beschreibung 4 2. Abkürzungsverzeichnis 5 3. Einleitung 6 Überblick über die purinerge Signalübertragung 6 Pathophysiologische Bedeutung des P2X7-Rezeptors 8 Speziesspezifische Eigenschaften des P2X7-Rezeptors 10 P2X7-Rezeptoren in der Pharmakotherapie 10 Rationale der Studie 11 Clemastin 12 Ivermectin 12 Die Neuroleptika Prochlorperazin und Trifluoperazin 13 4. Publikationen 15 5. Zusammenfassung der Arbeit 64 6. Literaturverzeichnis 68 7. Anlagen 74 Erklärung über die eigenständige Abfassung der Arbeit 74 Lebenslauf 75 Danksagung 76

Mon étude a porté sur le rôle du récepteur purinergique P2X7 (P2X7R) dans les processus physiopathologiques impliqués dans le développement des maladies auto-immunes de type lupique. Les souris MRL/lpr, déficientes en récepteurs d’apoptose Fas (mutation lpr), développent spontanément ces pathologies suite à l’accumulation lymphocytes T pathogéniques CD4−CD8− (DN) B220+ dans les organes lymphoïdes secondaires. Nous avons observé que ces lymphocytes ont également un déficit d’expression en P2X7R à leur surface. Cela nous a amené à postuler que P2X7R pourrait jouer un rôle clé dans l’homéostasie des lymphocytes T et le développement du lupus. Afin de vérifier notre hypothèse, nous avons produit des souris C57BL/6J (B6) déficientes simultanément pour Fas (lpr) et P2X7R (P2X7KO). Ces souris présentent une accumulation massive de lymphocytes T DN B220+ et des titres très élevés en auto-anticorps et en cytokines proinflammatoires ce qui n’est pas le cas pour les souris B6 simples mutantes lpr ou P2X7KO confirmant pour la première fois l’implication de P2X7R dans l’homéostasie des lymphocytes T, en synergie avec le récepteur Fas. Les lymphocytes T DN pathogéniques responsables de la lymphoaccumulation sont issues majoritairement de la sous populations des lymphocytes T CD8+. L’inflammation chronique présente chez les souris B6/lpr P2X7KO induit l’activation de l’ensemble des populations lymphocytaires T CD4+ et CD8+ naïves conduisant à l’accumulation de lymphocytes T Effecteurs/Mémoires : EM et CM et atteignent parfois le stade exhausted PD1+TIM3+. Ces cellules accumulées CD4+, CD8+ et DN B220+ ont une capacité de réactivation réduite. Ce biais fonctionnel et phénotypique a été confirmé en comparant la réponse immunitaire adaptative anti-adénovirus entre des souris déficientes en Fas et/ou P2X7R. Les réponses cellulaires et humorales sont moins importantes dans les souris B6/lpr P2X7KO que B6, B6-P2X7KO. Ces réponses antivirales sont intermédiaires dans les souris B6/lpr. L’ensemble de ces résultats renforcent notre hypothèse sur le rôle synergique des récepteurs Fas et P2X7R dans l’homéostasie des lymphocytes T. Le taux d’apoptose induit par l’activation des récepteurs Fas ou P2X7R séparément est moins important dans les lymphocytes T CD8+ par rapport au lymphocytes T CD4+. La synergie Fas-P2X7R serait donc nécessaire pour l’homéostasie des lymphocytes T CD8+. Afin de préciser les mécanismes à l’origine de la maladie et d’identifier l’influence de chaque récepteur sur l’expression des loci de susceptibilité, nous avons séquencé les ARNm exprimés dans la rate et les ganglions lymphatiques des souris MRL/lpr avant et après le développement de l’auto-immunité ainsi que chez les souris B6, B6/lpr, B6 P2X7KO et B6/lpr P2X7KO. / My project aims to determine the role of the purinergic receptor P2X7 (P2X7R) in the pathophysiological processes involved in the development of autoimmune lupus-like syndrome. MRL/lpr mice, deficient for the cell death receptor Fas (lpr mutation), spontaneously develop this pathology following the accumulation of pathogenic B220+CD4−CD8− (DN) T lymphocytes in secondary lymphoid organs. We have observed that these lymphocytes are also deficient in P2X7R cell surface expression. This led us to hypothesize that P2X7R could play a key role in T cell homeostasis and lupus development. To test our hypothesis, we produced B6 mice deficient for both Fas (lpr) and P2X7R (P2X7KO). These mice, but not single mutant B6 mice (lpr or P2X7KO), develop a massive accumulation of DN B220+ T lymphocytes and high levels of autoantibodies and proinflammatory cytokines, confirming for the first time the involvement of P2X7R in T-cell homeostasis. I have found that the pathogenic DN T lymphocytes are predominantly derived from the CD8+ T lymphocyte subpopulation. Chronic inflammation in B6/lpr P2X7KO mice induces the activation of the whole CD4+ and CD8+ naïve T lymphocyte subpopulations leading to the accumulation of Effector/Memory and exhausted T lymphocytes. Accumulated T-cells lose the ability to be reactivated. To confirm these results, I compared the adaptive immune response against adenovirus between mice deficient for Fas (lpr mutation), P2X7R-deficient mice or both receptors. The cellular and the humoral responses were lower in the B6/lpr-P2X7KO mouse strain compared to B6, B6-P2X7KO and B6/lpr mouse strains. The antiviral immune response in the B6/lpr mice was lower than in B6 and B6-P2X7KO mice. These results reinforce our hypothesis about the synergistic role of both receptors in the maintaining of T cell homeostasis. Ours results suggest that Fas and P2X7R play their synergistic role in T-cell homeostasis. In collaboration with a team from the University of Taiwan, we sequenced the mRNAs expressed in the spleen and lymph nodes of MRL/lpr mice before and after the onset of the diseases as well as in the B6, B6/lpr, B6 P2X7KO and B6/lpr P2X7KO mouse strains in order to better understand the mechanism triggering the disease and to identify the role of each receptor on the expression of the susceptibility loci.

INTRODUCTION: The cornea forms the anterior-most barrier of the eye, consisting of a non-keratinized pseudostratified squamous epithelium, a collagen-based stroma, and an endothelium. It is completely avascular, yet the most densely innervated structure in the human body. The sensory nerves project from the ophthalmic branch of the trigeminal cranial nerve into the limbal/stromal interface. From there, the nerves branch and ascend into Bowman’s membrane, a basal lamina delineating the epithelium from the stroma, and project into the epithelium as free nerve endings. Injury to the corneal epithelium can potentially lead to impaired vision if the wound healing process is not properly initiated. Immediately after injury, nucleotides such as ATP are released and bind to purinergic receptors known to be located in epithelial cell membranes, thereby initiating epithelial cell migration to close the wound. Malfunctions in the interactions between the corneal nerves and their epithelial counterparts during the wound healing process are thought to contribute to the attenuated wound healing characteristic of diabetes. However, the precise nature of these interactions, how they facilitate wound healing, and how they are impaired in diabetes, is not well understood. OBJECTIVES: Previously, our lab has shown that a member of purinergic family receptors (P2X7) is localized in the basal epithelial cells and becomes relocated to the leading edge of the wound after injury. When the relocation is inhibited, migration is attenuated. Additionally, it is known that diabetic mouse models display slower wound healing rates. The present study has three aims: (1) to replicate the characteristic sub-basal whorl organization of the corneal nerves in organ-cultured corneas; (2) to elucidate the connections between patterns of corneal innervation and purinergic receptor expression; and (3) to understand how these patterns interact to facilitate normal wound healing and how these interactions are disrupted in a diabetic model. METHODS: Our approach was to use immunohistochemistry of dissected mouse and to visualize the tissue using confocal microscopy. Sensory innervation profiles from diet induced obesity (DIO) mouse corneas and their wildtype C57Bl6 counterparts were compared in unwounded and wounded tissue. To image the nerves a methanol fixation protocol was optimized to examine the sub-basal plexus and the apical nerves. Corneas were dissected, stained with beta III-tubulin, which identifies nerves, and with an antibody to the P2X7 purinergic receptor, which is expressed in the epithelium and nerves. Trephine induced epithelial abrasion injuries were made on separate DIO and control models to compare re-epithelialization and re-innervation between the diseased and healthy states. Corneas were imaged using a Zeiss LSM 700 laser scanning confocal microscope and optical images were taken through the cornea over a distance averaging 115 microns. Corneas were imaged using a macro tiling plugin, stitching 3x3 optical z-stacks into composite images. The 3x3 tiles were created to image the central whorl, as well as the peripheral nerve fibers. Co-localization of P2X7 and betaIII tubulin were determined by thresholding using ImageJ/FIJI software. RESULTS: The elegant organization of the centralized sub-basal whorl of the control mouse was disrupted in the DIO mouse cornea, appearing fragmented and incomplete. Analysis of 7.5 and 15 wk corneas showed the whorl to be present at 7.5 wks. Average apical nerve fiber projection length was decreased in DIO cornea. Yet, analyses at each epithelial layer demonstrated overall increased apical nerve density in the DIO corneas as compared to control while sub-basal nerve density decreased dramatically. Stromal nerves remained equivalent. P2X7 did co-localize to the large stromal nerve fibers but it was difficult to show the localization along the sub-basal nerve plexus. However in cross-section images, P2X7 displayed an intracellular polarity, and was present along the apical surface of the columnar basal epithelial cells lining the basement membrane. This localization may suggest the presence of P2X7 expressing sensory nerves, which may be ideally poised for communication with the basal cells after injury. CONCLUSIONS: These data support the hypothesis that there is indeed a difference between diabetic and control corneal innervation. While wound healing differences due to the interaction between sensory nerves and the localization of P2X7 in epithelium at the leading edge remain to be fully elucidated, the novel finding of P2X7 expression in corneal nerves confirms a potential role of purinergic receptor and nerve coordination in conducting the wound healing response.

Lymphocytes from patients with B-chronic lymphocytic leukemia (B-CLL) express large numbers of P2X7 receptors for extracellular adenosine triphosphate (ATP). Activation of P2X7 receptors induces multiple downstream effects, of which the best documented is the opening of an ionic channel that is selective for divalent cations. Another effect of ATP is to induce the shedding of L-selectin (CD62L), a molecule which is involved in the adhesive interactions of lymphocytes on endothelial cells. High levels of soluble L-selectin and CD23 are found in the serum of patients with B-CLL, although the mechanisms involved in their production are poorly characterized. Because extracellular ATP causes shedding of L-selectin, we studied the effect of ATP on shedding of CD23, an adhesion molecule expressed on the surface of B-CLL lymphocytes. ATP induced the shedding of CD23 at an initial rate of 12% of that for L-selectin, while the EC50 of ATP (35 uM) and BzATP (10 uM) was identical for shedding of both molecules. Inactivation of the P2X7 receptor by pre-incubation with OxATP, an irreversible inhibitor of P2X7 purinoceptor, abolished ATP-induced shedding of both molecules. Moreover, KN-62, the most potent inhibitor for the P2X7 receptor inhibited ATP-induced shedding of both CD23 and L-selectin with the same IC50 (12 nM). Ro 31-9790, a membrane permeant zinc chelator which inhibits the phorbol-ester stimulated shedding of L-selectin also inhibited shedding of CD23 from B-CLL lymphocytes, but the IC50 was different for the two shed molecules (25 versus 1 ug/ml respectively). Although L-selectin was completely shed by incubation of cells with phorbol-ester no CD23 was lost under these conditions. Also, Ca2+ inhibits ATP-induced CD23 shedding but not L-selectin shedding. Since soluble CD23 and L-selectin are found in the serum of normal subjects and B-CLL patients, the expression of these two adhesion molecules on lymphocytes before and after transendothelial migration was studied in an in vitro model of this process. In normal and B-CLL subjects, 71�b5% of L-selectin from both T and B cells and 90% of CD23 from B cells was lost following transmigration, while the expression of a range of other adhesion molecules such as VLA-4, ICAM-1, LFA-1 and CD44 was unchanged. Lymphocytes incubated with OxATP retained their capacity for transendothelial migration and showed the same loss of L-selectin as control leukaemic lymphocytes. Ro 31-9790, which can protect ATP-induced both L-selectin and CD23 shedding, had no effect on inhibiting L-selectin and CD23 lost during transmigration. These data show the presence of a second pathway for the downregulation of L-selectin and CD23 from the lymphocyte surface. Data in vivo from 'knock-out' mice show that L-selectin is essential for the emigration of lymphocytes through high endothelial venules into lymph nodes. The migration of normal and B-CLL lymphocytes across confluent human umbilical vein endothelial monolayers was studied in an in vitro model of this process. Lymphocytes treated with ATP or BzATP showed 56�b25% or 67�b16% loss of L-selectin on the surface and 36�b24% or 64�b19% decrease of transmigration, respectively, while OxATP, which does not alter the L-selectin level, had no effect on lymphocyte transmigration. Further experiments examined this correlation between L-selectin expression and lymphocyte transendothelial migration in this model system. A quantitative assay for cell surface L-selectin showed that expression of L-selectin was lower on B-CLL lymphocytes (8,880�b5,700 molecules/cell) than on normal lymphocytes (29,500�b7,500 molecules/cell, p less than 0.001). Also the rate of transmigration of B-CLL lymphocytes (1.5�b0.9 migrated cells/HUVEC) was lower than normal peripheral lymphocytes (2.4�b0.9 migrated cells/HUVEC, p=0.04). Incubation of lymphocytes in complete medium for 24 hrs increased the expression of L-selectin on B-CLL lymphocytes by 1.5 to 2 fold while the normal lymphocyte L-selectin remained at the initial level. This upregulation of B-CLL L-selectin correlated with a 2 fold increased rate of transendothelial migration. A correlation was found between L-selectin expression on lymphocytes and their ability for transendothelial migration (r^2=0.6). This study shows that the adhesion molecules L-selectin and CD23 can be lost from lymphocytes by two different physiological pathways. One is by P2X7 receptor activation by extracellular ATP while the second is activated by transendothelial migration of these cells. A second finding is that B-CLL lymphocytes have lower level of L-selectin expression and an impaired ability for transendothelial migration compared with normal peripheral blood lymphocytes. Do these results explain the high serum levels of soluble L-selectin and CD23 observed in B-CLL? Although B-CLL lymphocytes do not recirculate as rapidly as normal peripheral blood lymphocytes, the greatly increased number of leukaemic cells in B-CLL ensures that much more soluble L-selectin and CD23 is generated during the recirculation of these cells through the body.

Lymphocytes from patients with B-chronic lymphocytic leukemia (B-CLL) express large numbers of P2X7 receptors for extracellular adenosine triphosphate (ATP). Activation of P2X7 receptors induces multiple downstream effects, of which the best documented is the opening of an ionic channel that is selective for divalent cations. Another effect of ATP is to induce the shedding of L-selectin (CD62L), a molecule which is involved in the adhesive interactions of lymphocytes on endothelial cells. High levels of soluble L-selectin and CD23 are found in the serum of patients with B-CLL, although the mechanisms involved in their production are poorly characterized. Because extracellular ATP causes shedding of L-selectin, we studied the effect of ATP on shedding of CD23, an adhesion molecule expressed on the surface of B-CLL lymphocytes. ATP induced the shedding of CD23 at an initial rate of 12% of that for L-selectin, while the EC50 of ATP (35 uM) and BzATP (10 uM) was identical for shedding of both molecules. Inactivation of the P2X7 receptor by pre-incubation with OxATP, an irreversible inhibitor of P2X7 purinoceptor, abolished ATP-induced shedding of both molecules. Moreover, KN-62, the most potent inhibitor for the P2X7 receptor inhibited ATP-induced shedding of both CD23 and L-selectin with the same IC50 (12 nM). Ro 31-9790, a membrane permeant zinc chelator which inhibits the phorbol-ester stimulated shedding of L-selectin also inhibited shedding of CD23 from B-CLL lymphocytes, but the IC50 was different for the two shed molecules (25 versus 1 ug/ml respectively). Although L-selectin was completely shed by incubation of cells with phorbol-ester no CD23 was lost under these conditions. Also, Ca2+ inhibits ATP-induced CD23 shedding but not L-selectin shedding. Since soluble CD23 and L-selectin are found in the serum of normal subjects and B-CLL patients, the expression of these two adhesion molecules on lymphocytes before and after transendothelial migration was studied in an in vitro model of this process. In normal and B-CLL subjects, 71�b5% of L-selectin from both T and B cells and 90% of CD23 from B cells was lost following transmigration, while the expression of a range of other adhesion molecules such as VLA-4, ICAM-1, LFA-1 and CD44 was unchanged. Lymphocytes incubated with OxATP retained their capacity for transendothelial migration and showed the same loss of L-selectin as control leukaemic lymphocytes. Ro 31-9790, which can protect ATP-induced both L-selectin and CD23 shedding, had no effect on inhibiting L-selectin and CD23 lost during transmigration. These data show the presence of a second pathway for the downregulation of L-selectin and CD23 from the lymphocyte surface. Data in vivo from 'knock-out' mice show that L-selectin is essential for the emigration of lymphocytes through high endothelial venules into lymph nodes. The migration of normal and B-CLL lymphocytes across confluent human umbilical vein endothelial monolayers was studied in an in vitro model of this process. Lymphocytes treated with ATP or BzATP showed 56�b25% or 67�b16% loss of L-selectin on the surface and 36�b24% or 64�b19% decrease of transmigration, respectively, while OxATP, which does not alter the L-selectin level, had no effect on lymphocyte transmigration. Further experiments examined this correlation between L-selectin expression and lymphocyte transendothelial migration in this model system. A quantitative assay for cell surface L-selectin showed that expression of L-selectin was lower on B-CLL lymphocytes (8,880�b5,700 molecules/cell) than on normal lymphocytes (29,500�b7,500 molecules/cell, p less than 0.001). Also the rate of transmigration of B-CLL lymphocytes (1.5�b0.9 migrated cells/HUVEC) was lower than normal peripheral lymphocytes (2.4�b0.9 migrated cells/HUVEC, p=0.04). Incubation of lymphocytes in complete medium for 24 hrs increased the expression of L-selectin on B-CLL lymphocytes by 1.5 to 2 fold while the normal lymphocyte L-selectin remained at the initial level. This upregulation of B-CLL L-selectin correlated with a 2 fold increased rate of transendothelial migration. A correlation was found between L-selectin expression on lymphocytes and their ability for transendothelial migration (r^2=0.6). This study shows that the adhesion molecules L-selectin and CD23 can be lost from lymphocytes by two different physiological pathways. One is by P2X7 receptor activation by extracellular ATP while the second is activated by transendothelial migration of these cells. A second finding is that B-CLL lymphocytes have lower level of L-selectin expression and an impaired ability for transendothelial migration compared with normal peripheral blood lymphocytes. Do these results explain the high serum levels of soluble L-selectin and CD23 observed in B-CLL? Although B-CLL lymphocytes do not recirculate as rapidly as normal peripheral blood lymphocytes, the greatly increased number of leukaemic cells in B-CLL ensures that much more soluble L-selectin and CD23 is generated during the recirculation of these cells through the body.