Spleen is a primary site for activation of platelet-reactive T and B cells in patients with immune thrombocytopenic purpura

We have recently reported that in patients with chronic immune thrombocytopenic purpura (IMTP), circulating T and B cells that are responsive to gpIIb-IIIa can induce anti-platelet autoantibody production. In this study, the frequencies and activation status of gpIIb-IIIa-reactive T and B cells were evaluated in the peripheral blood and spleen obtained from nine IMTP patients undergoing splenectomy. There was no difference in gpIIb-IIIa-reactive T cell frequencies between peripheral blood and spleen (6.4 ± 2.6 vs 5.2 ± 2.4 per 10⁵ T cells), as determined by limiting dilution analysis, but activated T cells responsive to gpIIb-IIIa showing accelerated proliferation kinetics and those expressing CD154 were more frequent in spleen than in peripheral blood. The frequencies of anti-gpIIb-IIIa Ab-producing B cells, as determined by ELISPOT assay, were also similar in peripheral blood and spleen (61.2 ± 24.0 vs 77.7 ± 45.3 per 10⁵ B cells); however, an anti-gpIIb-IIIa Ab was spontaneously produced by splenocytes in vitro, but scarcely secreted by PBMCs. CD19^-/surface Ig^-/CD38⁺/CD138⁺ plasma cells secreting anti-gpIIb-IIIa Ab were exclusively detected in the spleen. In serial analysis, the frequencies of circulating gpIIb-IIIa-reactive T and B cells were decreased after splenectomy in patients with a complete response, but were unchanged in nonresponders. These findings indicate that an interaction between gpIIb-IIIa-reactive T and B cells inducing anti-platelet Ab production in IMTP patients occurs primarily in the spleen and that the significant number of gpIIb-IIIa-reactive T and B cells activated in the spleen are released into the circulation as memory cells.