Sperm-­-egg membrane interaction and fusion is mediated by various molecules of the different protein network that are located on both egg and sperm membrane. So far, many proteins have been selected to be fusion candidates, some of them (Izumo1, CD9, Juno) were proven to be essential, whereas others were discovered to play an unsuspected new active role (CD46, tetraspanins). After the adhesion of sperm to an egg, Juno located on the oolema associates with monomeric Izumo1 on sperm membrane, which is results in Izumo1 dimerization following quick removal of Juno from the egg surface as described in mouse. It implies that additional receptor on the egg membrane is required to play a role in sperm-­-egg fusion. To find a human fusogenic receptor for IZUMO1 protein we used one-­-bead-­-one-­-compound (OBOC) assay, a random screening approach. A bead, fulfilling all the requirements when interacting with the human sperm, carried a peptide sequence showing homology with the conserved Ig domain of the human specific Fc receptor-­-like protein 3 (FcRL3). In general, the ...

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The dichotomy between type 1 and 2 conventional DCs under steady-state conditions is well defined. Bosteels et al. demonstrate that, upon inflammation, cDC2s acquire a hybrid inf-cDC2 phenotype, sharing phenotype, gene expression, and function with cDC1s and monocyte-derived cells, to optimally boost CD4 and CD8 immunity via Fc receptors.

The Fas pathway is critical for the maintenance of normal T cell homeostasis. Humans and mice with defects in this pathway exhibit the accumulation of large numbers of peripheral lymphocytes and lupus-like autoimmunity. A major feature of these organisms is the accumulation of non-NK TCRαβ+CD4-CD8- “double negative” (DN) T cells. While regulatory T cells (Tregs) with the DN phenotype have been extensively characterized in Fas-sufficient mice and humans, limited data exist on the role of DN T cells as Tregs in Fas-deficient animals. In fact, most of the literature suggests that the DN T cells accumulating in Fas-deficiency states are pathogenic, contributing to secondary lymph node enlargement and autoimmune disease. In this body of work, data are presented that illustrate that Fas-deficient lymphoproliferative (LPR) DN T cells can act as Tregs in an interferon γ (IFNγ)- and Fas ligand (FasL)-dependent fashion toward Fas-sufficient T cells. LPR DN T cells needed to be able to secrete and respond to IFNγ in order to upregulate surface FasL, in order to ameliorate GVHD mediated by CD4+ T cells in vivo and to suppress the proliferation of and kill activated CD4+ T cells in vitro. FcRγ, a key molecule involved in innate immune responses, can substitute for CD3ζ in the T cell receptor (TCR) of mouse and human T cells in certain circumstances; in doing so, it is essential for the regulatory function of TCR transgenic DN Tregs. FcRγ-deficient LPR mice were found to have exacerbated T cell accumulation and early mortality. We show that while FcRγ expression was required for LPR DN T cells to regulate CD4+ and CD8+ T cells responding to alloantigens in vitro and in vivo, it does not control autologous lymphoproliferation in LPR mice by supporting the function of a regulatory cell, nor does it affect the rate of proliferation of LPR T cells in vivo. Instead, FcRγ-expressing LPR CD4+, CD8+ and DN T cells were found to be undergoing apoptosis at a high rate in vivo, and in contrast to their FcRγ-deficient counterparts, FcRγ+ LPR DN T cells were capable of undergoing TCR restimulation-induced cell death (RICD). The data presented in this thesis therefore show that LPR DN T cells can exhibit IFNγ-, FasL- and FcRγ-dependent regulatory function, and also illustrate a previously unknown function for FcRγ in controlling the expansion of Fas-deficient T cells. The implications of these data for autoimmune lymphoproliferative syndromes, and normal T cell homeostasis, are discussed.

The Fas pathway is critical for the maintenance of normal T cell homeostasis. Humans and mice with defects in this pathway exhibit the accumulation of large numbers of peripheral lymphocytes and lupus-like autoimmunity. A major feature of these organisms is the accumulation of non-NK TCRαβ+CD4-CD8- “double negative” (DN) T cells. While regulatory T cells (Tregs) with the DN phenotype have been extensively characterized in Fas-sufficient mice and humans, limited data exist on the role of DN T cells as Tregs in Fas-deficient animals. In fact, most of the literature suggests that the DN T cells accumulating in Fas-deficiency states are pathogenic, contributing to secondary lymph node enlargement and autoimmune disease. In this body of work, data are presented that illustrate that Fas-deficient lymphoproliferative (LPR) DN T cells can act as Tregs in an interferon γ (IFNγ)- and Fas ligand (FasL)-dependent fashion toward Fas-sufficient T cells. LPR DN T cells needed to be able to secrete and respond to IFNγ in order to upregulate surface FasL, in order to ameliorate GVHD mediated by CD4+ T cells in vivo and to suppress the proliferation of and kill activated CD4+ T cells in vitro. FcRγ, a key molecule involved in innate immune responses, can substitute for CD3ζ in the T cell receptor (TCR) of mouse and human T cells in certain circumstances; in doing so, it is essential for the regulatory function of TCR transgenic DN Tregs. FcRγ-deficient LPR mice were found to have exacerbated T cell accumulation and early mortality. We show that while FcRγ expression was required for LPR DN T cells to regulate CD4+ and CD8+ T cells responding to alloantigens in vitro and in vivo, it does not control autologous lymphoproliferation in LPR mice by supporting the function of a regulatory cell, nor does it affect the rate of proliferation of LPR T cells in vivo. Instead, FcRγ-expressing LPR CD4+, CD8+ and DN T cells were found to be undergoing apoptosis at a high rate in vivo, and in contrast to their FcRγ-deficient counterparts, FcRγ+ LPR DN T cells were capable of undergoing TCR restimulation-induced cell death (RICD). The data presented in this thesis therefore show that LPR DN T cells can exhibit IFNγ-, FasL- and FcRγ-dependent regulatory function, and also illustrate a previously unknown function for FcRγ in controlling the expansion of Fas-deficient T cells. The implications of these data for autoimmune lymphoproliferative syndromes, and normal T cell homeostasis, are discussed.

Low affinity Fcg receptor III (FcgRIII, CD16) triggers a variety of cellular events upon binding to the Fc portion of IgG. A real-time flow cytometry method was developed to measure the affinity and kinetics of such low affinity receptor/ligand interactions, which was shown as an easily operated yet powerful tool. Results revealed an unusual temperature dependence of reverse rate of CD16aTM dissociating from IgG. Except for a few studies using mammalian cell CD16s, most kinetics analyses use purified aglycosylated extracellular portion of the molecules, making it impossible to assess the importance of the receptor anchor and glycosylation on ligand binding. We used a micropipette adhesion frequency assay to demonstrate that the anchor length affects the forward rate and affinity of CD16s for IgG in a species specific manner, most likely through conformational changes. Receptor glycosylation dramatically reduced ligand binding by 100 folds. T cell receptor (TCR) is arguably the most important receptor in the adaptive human immune system. Together with coreceptor CD4 or CD8, TCR can discriminate different antigen peptides complexed with major histocompatibility complex (MHC) molecule (pMHC), which differ by as few as only one amino acid, and trigger different T cell responses. When T cell signaling was suppressed, TCR had similar affinity and kinetics for agonist and antagonist pMHC whose binding to CD8 was undetectable. TCR on activated T cell had a higher affinity for pMHCs, suggesting that TCRs organize themselves differently on activated T cells than on naïve T cells. In the absence of inhibitors for signaling, TCR binds agonist pMHC with several orders of magnitude higher affinity than antagonist pMHC. In addition, engagement of TCR by pMHC signals an upregulation of CD8 binding to pMHC, which is much stronger than the TCR-pMHC binding. The transition from weak TCR binding to the strong CD8 binding takes place around 0.75 second after TCR in contact with pMHC and can be reduced by several inhibitors of tyrosine and lipid phosphorylation, membrane rafts, and actin cytoskeleton. These results provide new insights to understanding T cell discrimination.

La pharmacocinétique (PK) des anticorps monoclonaux (mAbs) est sujette à d’importantes variations interindividuelles. Le récepteur néonatal au Fc des IgG (FcRn) et le statut immun à l’encontre de ces mAbs sont des déterminants de cette PK. La bioconjugaison des mAbs à des cytotoxiques entraîne une altération de leur PK. Nous montrons que le taux de couplage modifie l’affinité de ces espèces pour le FcRn à pH6. La proportion d’agrégats au sein des solutions d’anticorps armés augmente avec le taux de couplage et pourrait entraîner une altération de leur PK. Par ailleurs, cette agrégation est impliquée dans l’immunogénicité des mAbs, et nous avons donc cherché à identifier des acides aminés impliqués dans l’agrégation de mAbs indiqués en clinique. Il apparait que la nature biochimique de résidus des paratopes pourrait augmenter cette agrégation. Les anti-TNF- présentent très peu d'agrégats et figurent pourtant parmi les plus immunogènes chez l’Homme. Nous avons donc exploré le rôle des complexes immuns dans leur immunogénicité chez la souris. Il apparait que la présence du FcRn n’est pas à l’origine de l’immunisation contre ces mAbs, contrairement à celle des complexes immuns. Ces résultats donnent des pistes pour la production de mAbs plus efficients et mieux tolérés. / The pharmacokinetic (PK) profile of monoclonal antibodies (mAbs) shows interindividudal variability. The neonatal Fc receptor (FcRn) and the immounogenicity of these mAbs are determinative factors of mAb PK. Generation of antibody-drug-conjugates alters their PK profile. We show that the the affinity for FcRn at pH6 increases with the drug-to-mAb ratio, as does the amount of aggregates inside the mAb-drug-conjugate. The amount of aggregates could be responsible for an avidity effect towards FcRn. These aggregates are known to cause immunogenicity, so we studied biochemical determinants inside the aminoacid sequence of marketed mAbs. We show that the biochemical nature of some aminoacids inside the paratope has an impact on the amount of aggregation. Anti-TNF- mAbs show very little aggregation but are very immunogenic in humans. We studied the role of the formation of immune complexes in the immunization against anti-TNF- mAbs in mice, and showed that immune complexes, but not FcRn are essential in the immunization process against anti- TNF- mAbs. These results give leads towards the generation of more efficient, better tolerated mAbs.

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