IVIg-Primed Splenocytes Ameliorate Murine ITP in an MHC Class II-Unrestricted Manner.

We have previously demonstrated that IVIg-primed leukocytes can, upon transfer to naïve mice, completley recapitulate the therapeutic effects of IVIg in treating immune thrombocytopenia in a murine model. Dendritic cells (DC) appear to be the primary cellular target of IVIg in this model. The exact pathway by which IVIg-primed DC inhibit platelet clearance remains, however, unknown. DC are professional antigen presenting cells of haematopoietic origin that are specialized for the capture, processing and presentation of antigens to T cells via their MHC Class II. This primary function of DC is absolutely dependent on MHC Class II expression. Herein, we have evaluated the efficacy of action of IVIg-primed splenocytes from MHC mismatched mice in the amelioration of murine ITP. Mice expressing the Class II haplotype I-A^b (C57BL/6) were injected intravenously with IVIg-primed splenocytes from syngeneic mice, or Balb/C mice (Class II haplotype I-A^d /I-E^d) or CD1 mice (outbred, mixed Class II haplotype I-A/E) prior to the induction of thrombocytopenia by an anti-platelet antibody. We found that IVIg-primed splenocytes from all strains of mice tested were able to successfully ameliorate thrombocytopenia in C57BL/6 mice, regardless of Class II haplotype. None of the splenocytes primed with a control protein, BSA, ameliorated thrombocytopenia. To confirm our findings that IVIg-primed splenocytes function independent of MHC haplotype, we next employed IVIg-primed splenocytes from MHC Class II deficient mice and found these splenocytes were also able to successfully ameliorate murine thrombocytopenia. These data demonstrate a non-MHC-restricted function for DC in IVIg function, and suggest that IVIg-primed DC function occurs independent of MHC Class II expression in the amelioration of murine ITP. In addition, since this potential new cell-based therapy for ITP is not MHC-restricted, we speculate that IVIg-primed DC from any donor (including autologous) could theoretically be used to treat individuals with ITP or other autoimmune diseases without the requirement for donor matching.