The transcription factor Pax5 is essential for commitment to the B lineage as the development of these cells is arrested at an early stage in the bone marrow of Pax5 deficient mice. Pax5 deficient pro-B cells display remarkable plasticity and are able to differentiate into other cell lineages both in vitro and in vivo. Several Pax5 target genes have been previously reported but none are able to explain the developmental block observed at the early to late pro-B cell stage. To determine the exact mechanisms by which Pax5 controls B cell development, I have undertaken a cDNA microarray screen with a custom generated B cell-specific cDNA library. By identifying genes that are differentially expressed between Pax5 deficient and wild type pro-B cells, I have identified a number of potential Pax5 target genes. The microarray screen identified lymphoid-restricted membrane protein (Lrmp or Jaw1) as a novel Pax5 activated transcript. Using RT-PCR and a Pax5-estrogen receptor inducible system, I confirmed that Jaw1 is a direct Pax5 target gene whose expression is confined, in resting cells, to the earliest stages of B and T cell development. The biological relevance of Jaw1 for cell fate specification has been tested by transducing bone marrow progenitor cells with murine retroviral vectors and reconstituting haemopoiesis in vivo. I have reported that over-expression of Jaw1 in these cells results in a decrease in the development of B and NK lymphocytes and a marked increase in the development of myeloid cells in the bone marrow of reconstituted mice. This result suggests that Jaw1 may play an important role in the early development of lymphocytes in the bone marrow. Whilst initial analysis of Jaw1 deficient mice has revealed no overt defects in lymphopoiesis, I postulate that Jaw1 is involved in IP3-induced calcium signaling downstream of the pre-BCR and BCR. This hypothesis has resulted from analysis of the function of IRAG, the only known Jaw1 homologue combined with data that Jaw1 is expressed in early B cells in the BM as well as in germinal centers in the spleen. Pax5 mutant mice usually die before weaning and the cause of death is currently unknown, suggesting that Pax5 is expressed in a previously unreported tissue. To investigate this hypothesis I produced a monoclonal antibody to Pax5 and screened for novel expression domains during embryonic development and also in neonate mice. These studies did not detect any new Pax5 expression domains, but did reveal that this antibody cross-reacts with Pax2 and/or Pax8 in the developing kidney and brain. Biochemical analysis of the serum from Pax5 deficient mice also did not reveal the likely cause of death in these animals, beyond the general signs of dehydration and starvation that are likely to be secondary to the underlying defect. / Doctor of Philosophy (PhD)

B cell chronic lymphocytic leukemia (B-CLL) is a hematologic neoplasm characterised by the proliferation and accumulation of sIgM+/D+ B cells that fail to progress to the final stages of B cell development. The malignant cells in B-CLL also express the pan-T cell antigen CD5, suggesting that CLL is a malignancy of the CD5+ subset of B cells. Additional characteristics of the malignant clone include a low proliferative index, enhanced in vivo survival and constitutive expression of the anti-apoptosis oncoprotein bcl-2. The behaviour of leukemic CD5 B cells in vitro contrasts their arrested in vivo state. That is, despite the majority of cells being arrested in the G0 phase of the cell cycle, the leukemic B cells are not irreversibly frozen as they can be induced to differentiate to Ig-secreting cells under appropriate in vitro conditions. Furthermore, leukemic CD5 B cells rapidly undergo death by apoptosis following in vitro culture. This thesis describes the requirements for in vitro activation of leukemic CD5+ B cells, the characterisation of the events involved in apoptosis of these cells as well as the identification of various growth factors capable of modulating these events. Stimulation of unfractionated peripheral blood lymphocytes (PBLs) from three patients with B-CLL with the phorbol ester PMA and the mitogens PHA and PWM resulted in significant increases in cell proliferation, RNA synthesis and 1gM secretion when compared to unstimulated cell populations. PMA was the most potent inducer of 1gM secretion and this occurred irrespective of the presence of residual T cells. PMA-induced proliferation and RNA synthesis were also independent of T cells. However, in the presence of T cells, these parameters of cellular activation were enhanced during in vitro culture. Thus, the inductive ability of PMA on leukemic CD5 B cells was independent of T cells. In contrast, activation and differentiation of the leukemic CD5 B cells into 1gM-secreting cells following culture with mitogens did not occur in the absence of T cells. Interestingly, co-stimulation of leukemic CD5+ B cells with PMA and anti-Ig induced cellular responses that exceeded those induced by either activator alone. Thus, leukemic CD5+ B cells from patients with B-CLL can be activated in vitro and differentiate in response to stimulation via both T cell-dependent and T cell-independent mechanisms. Apoptotic cell death was characterised in purified leukemic CD5 B cells obtained from six B-CLL patients. All leukemic CD5 B cell populations entered an apoptotic pathway in vitro as evidenced by a reduction in cell size, loss of cell viability and fragmentation of DNA into multimers of -180 base pairs. Following 24 hours of in vitro culture 24.0±16% of DNA was fragmented. After 8 days, the majority of DNA was fragmented, and fewer than 10% of cultured cells were viable. Examination of bcl-2 expression in the malignant B cells by flow cytometry revealed a unimodal pattern of expression in greater than 85% of cells from each B-CLL patient prior to culture. During in vitro culture, bcl-2 expression became bimodal such that the B cells displayed a bcl-2hjgh and bcl-2iow phenotype. The level of expression by the bCl2hjgh cells was similar to that observed prior to in vitro culture, indicating that bcl-2 is down-regulated in apoptosing cells. Interestingly, despite this downregulation, the overall number of cells positive for bcl-2 remained constant. This suggests that the enhanced survival of leukemic CD5+ B cells in vivo is mediated by the sustained expression of bcl-2 and that additional mechanisms exist capable of overriding the protective effect of bcl-2 when bcl-2 is present at reduced levels. Leukemic B cell apoptosis has previously been reported to be delayed or prevented by IL-4, IFN-y and IFN-a. These results were confirmed in this study where it was found that culture of leukemic CD5 B cells with IL-4 or IFN-y enhanced cell viability and delayed apoptosis in 6/6 and 5/6 populations of leukemic B cells, respectively. This function was also found to be shared by IL-2, IL-6, IL-13 and TNF-a as these cytokines enhanced cell viability and delayed apoptosis in some of the cell populations examined at a level similar to that observed for IL-4 and IFN-y. These cytokines may mediate their effect via the expression of bcl2 as culture in the presence of IL-2, IL-4, IL-6, IL-13, IFN-y or TNF-a resulted in a higher percentage of cells displaying the bcl-2high phenotype, compared to unstimulated cells. Taken together, these results suggest that autocrine and/or paracrine growth loops may play a role in the pathogenesis of B-CLL and that cytokines that prevent apoptosis in vitro may be targets for treatment of this B cell malignancy.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Chicago, Dept. of Pathology, August 1999. / Includes bibliographical references. Also availabel on the Internet.

<p>An immunological mechanism to account for the regulation of peripheral self-reactive T cells, which escape central tolerance in the thymus, during the primary activation of naïve, foreign antigen-specific T cells remains to be established. Contemporary models of primary T cell activation that attempt to describe how this occurs differ significantly in the cellular interactions necessary for naïve CD4+ T helper cell activation. It is generally accepted that most CD8+ T cells are dependent upon CD4+ T helper cells for their activation. </p><p>The Infectious Non-Self and Danger Models of CD4+ T cell activation propose that interaction of a naïve T cell with an appropriately armed dendritic cell is sufficient, whereas the Two-step, Two-signal Model proposes additional cellular interactions are necessary. The major goal of this thesis was to establish and utilize an in vitro experimental system that would allow one to begin to delineate which model most validly describes the cellular interactions required for generation of primary immune responses from naïve T cells. Employing a population of naïve T cells uncontaminated with any partially or fully activated cells is essential for such a study.</p><p>The results presented in this thesis show, that when thymocytes are employed as a source of responding naïve T cells, cellular interactions, in addition to interaction with bone marrow derived dendritic cells, are required for the activation of naïve thymic T cells. The primary activation of thymic T cells to generate CD4+ IL-2 producing cells, and CD8+ IFN-g producing cells and cytotoxic T cells upon stimulation with splenic allogeneic stimulator cells is critically dependent upon the presence of a syngeneic population of radiation resistant, CD4+ T cells found in the spleen of normal mice. Additionally, when such cells are present as a source of help for thymocytes, allogeneic bone marrow derived dendritic cells fail to stimulate the generation of optimal cytotoxic and cytokine responses from naïve thymic T cells. However, they do stimulate thymocytes to cycle and up regulate the ligand for the costimulatory molecule CD40, CD40L.</p><p>The results presented within also show that the optimal activation of naïve thymic T cells to generate CD4+ IL-2 producing cells, and CD8+ IFN-g producing cells and cytotoxic T cells, requires the presence of allo-MHC bearing Ig+ B220+ B cells. The removal of B220+ cells by magnetic cell sorting from the allogeneic spleen reveals that the generation of CD8+ cytotoxic T cells and IFN-g producing cells from thymocytes is markedly reduced compared to unsorted allogeneic spleen cells. However, IL-2 and IL-4 cytokine producing cells are still detectable. Potential reasons for the generation of the latter cytokine producing cells are discussed. The results presented in this thesis have revealed insights into the cellular interactions involved in the activation of naïve thymic T cells.

<p>An immunological mechanism to account for the regulation of peripheral self-reactive T cells, which escape central tolerance in the thymus, during the primary activation of naïve, foreign antigen-specific T cells remains to be established. Contemporary models of primary T cell activation that attempt to describe how this occurs differ significantly in the cellular interactions necessary for naïve CD4+ T helper cell activation. It is generally accepted that most CD8+ T cells are dependent upon CD4+ T helper cells for their activation. </p><p>The Infectious Non-Self and Danger Models of CD4+ T cell activation propose that interaction of a naïve T cell with an appropriately armed dendritic cell is sufficient, whereas the Two-step, Two-signal Model proposes additional cellular interactions are necessary. The major goal of this thesis was to establish and utilize an in vitro experimental system that would allow one to begin to delineate which model most validly describes the cellular interactions required for generation of primary immune responses from naïve T cells. Employing a population of naïve T cells uncontaminated with any partially or fully activated cells is essential for such a study.</p><p>The results presented in this thesis show, that when thymocytes are employed as a source of responding naïve T cells, cellular interactions, in addition to interaction with bone marrow derived dendritic cells, are required for the activation of naïve thymic T cells. The primary activation of thymic T cells to generate CD4+ IL-2 producing cells, and CD8+ IFN-g producing cells and cytotoxic T cells upon stimulation with splenic allogeneic stimulator cells is critically dependent upon the presence of a syngeneic population of radiation resistant, CD4+ T cells found in the spleen of normal mice. Additionally, when such cells are present as a source of help for thymocytes, allogeneic bone marrow derived dendritic cells fail to stimulate the generation of optimal cytotoxic and cytokine responses from naïve thymic T cells. However, they do stimulate thymocytes to cycle and up regulate the ligand for the costimulatory molecule CD40, CD40L.</p><p>The results presented within also show that the optimal activation of naïve thymic T cells to generate CD4+ IL-2 producing cells, and CD8+ IFN-g producing cells and cytotoxic T cells, requires the presence of allo-MHC bearing Ig+ B220+ B cells. The removal of B220+ cells by magnetic cell sorting from the allogeneic spleen reveals that the generation of CD8+ cytotoxic T cells and IFN-g producing cells from thymocytes is markedly reduced compared to unsorted allogeneic spleen cells. However, IL-2 and IL-4 cytokine producing cells are still detectable. Potential reasons for the generation of the latter cytokine producing cells are discussed. The results presented in this thesis have revealed insights into the cellular interactions involved in the activation of naïve thymic T cells.

No description available.

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

Although B cells are well-known for their functions in antibody production and antigen presentation, certain B cell subsets have been recently identified as regulatory B cells to modulate immune responses through cytokine production. However, the microenvironmental factors involved in the induction of regulatory B cells remain largely uncharacterized. B cell-activating factor (BAFF), a member of TNF family cytokines produced by myeloid cells, is a key regulator for B cell maturation and function. However, it remains unknown whether BAFF plays a role in modulating the generation of regulatory B cells and how regulatory B cells suppress autoimmune pathogenesis. In this study, treatment with BAFF significantly increased IL-10-producing B cells in culture of mouse splenic B cells, an effect specifically abrogated by neutralization with TACI-Fc. BAFF-induced IL-10-producing B cells showed a distinct CD1dhiCD5+(B10) phenotype. Phenotypic analysis further indicated that these BAFF-induced B10 cells were marginal-zone (MZ)-like B cells. Interestingly, BAFF treatment in vivo also increased the number of IL-10-producingB cells in splenic MZ regions. Moreover, chromatin immunoprecipitation analysis revealed that BAFF activated the transcription factor AP-1 for binding to IL-10 promoter, demonstrating a novel function for BAFF in inducing IL-10 production. Furthermore, those BAFF-induced B10 cells exhibited significant suppressive effects on CD4+T cell proliferation and Th1 cytokine production in culture. To explore whether these BAFF-induced B10 cells possess a regulatory function in suppressing autoimmune progression in vivo, collagen-induced arthritis (CIA) mouse model was employed. In vitro-expanded B10 cells and other control B cells were intravenously transferred into DBA/1J mice on the day of 2ndcollagen II (CII)-immunization. After adoptive transfer of BAFF-induced B10 cells, CII-immunized mice exhibited a delayed onset of arthritis and substantially reduced severity of clinical symptoms. The pathogenesis of IL-17-producing CD4+T cells (Th17) in the development of arthritis has been well-recognized, which has led me to test the hypothesis whether B10 cells ameliorate the development of arthritis via modulating Th17 cells. During the progression of CIA, IL-10-producing B cells were decreasedwhereasTh17 cells were significantly increased at the acute phase of CIA. Upon transfer of BAFF-induced B10 cells, a substantially reduction ofTh17 cells in both lymphoid organs and inflamed joints were detected. To verify whether B10 cells inhibit Th17 cell generation in culture, CFSE-labeled na?ve CD4+T cells were cocultured with B10 cells in Th17 cell polarization medium. It was found that B10 cells suppressed Th17 cell differentiation via reducing STAT3 phosphorylation and RORt expression. Although adoptive transfer of Th17 cells triggered the development of CIA in IL-17-/-DBA mice, cotransfer of B10 cells with Th17 cells profoundly delayed the onset of delayed the onset of arthritisand remarkably reduced the infiltration of Th17 cells in synovial fluid. Taken together, I have identified a novel function of BAFF in the induction of IL-10-producing regulatory B cells. My findings that adoptive transfer of BAFF-expanded B10 cells can effectively suppress the development of experimental arthritisin mice via the inhibition of Th17 cell generation may contribute to the development of new therapeutic strategies in treating human rheumatoid arthritis. / published_or_final_version / Pathology / Doctoral / Doctor of Philosophy

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