Proposed mechanisms for development of ITP may parallel those generated during vaccine responses. B cells are integral to the immune response in ITP through several mechanisms. These include the production of platelet and megakaryocyte-reactive antibodies (A), as well as antigen presentation (B), in which B-cell–T-cell interactions lead to costimulation resulting in an altered Th1/Th2 balance, clonal expansion of cytotoxic T cells, and release of inflammatory cytokines (C). The latter may stimulate macrophages and dendritic cells, enhancing clearance and destruction of antibody-coated platelets and altering the distribution of T-cell subsets. In the case of ITP, the antigen may be a viral peptide cross-reactive with platelet glycoproteins, platelet glycoproteins themselves following loss of tolerance, or others that have not been characterized. The response to vaccines likely parallels that to platelet glycoproteins depicted here. Adapted from Stasi9 with permission. Professional illustration by Paulette Dennis.
