Immune thrombocytopenia (ITP) is an autoimmune disorder, mediated mainly by autoantibodies against platelet glycoprotein GPIIbIIIa and GPIbα resulting in enhanced platelet destruction. Decreased platelet production and cellular immunity also contribute to ITP. GPIIbIIIa and GPIbα are distinct platelet receptors. Previous studies suggested that anti-GPIbα (versus anti-GPIIbIIIa)-mediated ITP is less responsive to IVIG therapy. However, little information is available whether antibody specificities also dictate efficacy of Glucocorticosteroids (GC), which are the first-line ITP treatment. Here, I first induced ITP in mice by passive administration of anti-GPIbα or anti-GPIIbIIIa antibodies. Results suggest GCs were more effective at amelioration of anti-GPIIbIIIa-mediated thrombocytopenia. I repeated this observation in an active ITP model, in which splenocytes from wild-type platelet immunized GPIbα-/- or GPIIIa-/- mice were engrafted into wild-type mice, which developed ITP. Thus, I established new murine models of ITP for GC therapy and demonstrated that anti-GPIbα-mediated thrombocytopenia may be less responsive to GC therapy.

Immune thrombocytopenia (ITP) is an autoimmune disorder, mediated mainly by autoantibodies against platelet glycoprotein GPIIbIIIa and GPIbα resulting in enhanced platelet destruction. Decreased platelet production and cellular immunity also contribute to ITP. GPIIbIIIa and GPIbα are distinct platelet receptors. Previous studies suggested that anti-GPIbα (versus anti-GPIIbIIIa)-mediated ITP is less responsive to IVIG therapy. However, little information is available whether antibody specificities also dictate efficacy of Glucocorticosteroids (GC), which are the first-line ITP treatment. Here, I first induced ITP in mice by passive administration of anti-GPIbα or anti-GPIIbIIIa antibodies. Results suggest GCs were more effective at amelioration of anti-GPIIbIIIa-mediated thrombocytopenia. I repeated this observation in an active ITP model, in which splenocytes from wild-type platelet immunized GPIbα-/- or GPIIIa-/- mice were engrafted into wild-type mice, which developed ITP. Thus, I established new murine models of ITP for GC therapy and demonstrated that anti-GPIbα-mediated thrombocytopenia may be less responsive to GC therapy.

Les cellules lymphoïdes innées (ILCs) sont des populations cellulaires d’identification récente, mais leur rôle in vivo chez l’homme reste mal connu. Dans une 1ère étude, nous avons pu montrer qu’un déficit sévère en NK au cours de déficits immunitaires communs variables est associé à un risque accru de manifestations non infectieuses et infectieuses bactériennes sévères, suggérant un rôle protecteur non redondant des cellules NK lorsque le système immunitaire adaptatif n’est pas fonctionnel. Dans une 2ème étude, nous avons montré que des patients atteints de déficits immunitaires combinés sévères ɣc et JAK3 déficients n’ont pas d’ILCs. Après allogreffe de moelle osseuse, le nombre d’ILCs circulantes reste indétectable, sans manifestation clinique notable associée. Ces résultats sont en faveur d’une redondance des fonctions des ILCs chez l’homme, lorsque les fonctions T et B sont conservées. Nous avons ensuite étudié les modifications phénotypiques et fonctionnelles des cellules NK au cours du purpura thrombopénique immunologique, et observé un défaut de production d’interféron-ɣ par les cellules NK circulantes et une augmentation de la cytotoxicité dépendante des anticorps des cellules NK spléniques. Une inhibition des fonctions des cellules NK par les immunoglobulines polyvalentes est également mise en évidence. Enfin, une étude des ILCs circulantes au cours de la maladie associée aux IgG4 ainsi qu’une revue de la littérature sur l’étude des ILCs au cours des pathologies inflammatoires sont rapportées. En conclusion, l’apparente redondance des ILCs chez l’homme ainsi que leur implication en pathologies inflammatoires en font de potentielles cibles thérapeutiques. / Innate lymphoid cells (ILCs) are recently identified components of the immune system, but their functions in vivo in humans are still elusive. In a first study, we show in patients with common variable immunodeficiency that non-infectious inflammatory complications and severe bacterial infections were more frequent in patients with severe NK cell lymphopenia, indicating potential non-redundant immune functions of NK cells when the adaptive immune response is not optimal. In a second study, we observe that in patients with ɣc and JAK3 severe combined immunodeficiencies, all ILC subsets are absent. After hematopoietic stem cell transplantation, ILCs remain indetectable with no susceptibility to disease, suggesting that ILCs might be redundant and dispensable in humans, if T and B cells functions are preserved. In the second part of this thesis, we study phenotypic and functional modifications of NK cell compartment in primary immune thrombocytopenia. Interferon gamma production by the peripheral blood NK cells of ITP patients is decreased. In contrast, splenic NK cells of ITP patients tend to be more efficient in antibody-dependent cell cytotoxicity. Intravenous polyvalent immunoglobulins lead to the inhibition of blood NK cell activation. Finally, we present the preliminary results of a study investigating the modifications of circulating ILCs in IgG4-related disease, and present an extensive litterature review concerning the role of ILCs in inflammatory diseases. In conclusion, the apparent redundancy of ILCs for protective immunity and their pathogenic role in inflammatory diseases make their targeting in humans for therapeutic purposes particularly promising.