T lymphocyte responses to RBC-derived microparticles are APC-dependent (P1040)

Abstract

Abstract Microparticles (MPs) generated in stored blood are thought to cause immunomodulatory effects in blood recipients. MPs are small double membrane vesicles derived from leukocytes, platelets or other cells. We hypothesized that RBC-derived MPs would inhibit T cell responses. MPs were isolated from stored RBCs using differential centrifugation. PBMCs were cultured +/-MPs, supernatants were collected on day one, and PBMC survival was tested on day seven. PBMCs or purified T cells were stained with CFSE and cultured for seven days with PHA+/-MP. We found that MPs alone induced pro-inflammatory cytokine secretion and enhanced survival of T cells, B cells, and NK cells to a similar degree, but did not induce T cell proliferation. MPs augmented PHA-induced proliferation of CD4+ and CD8+ T cells in PBMC cultures, and blockade of CD40 or CD40L accessory molecules prevented the augmentation effect of MPs on T cell proliferation. Furthermore, stimulation of purified T cells with PHA+/-MP did not induce T cell proliferation, and addition of MP-exposed and washed monocytes to purified T cells recapitulated augmentation of T cell proliferation. In summary, addition of RBC-MPs to PBMCs improved survival of unstimulated cells and augmented mitogen driven T cell responses in an APC-dependent manner. These results suggest that, contrary to our hypothesis, MPs found in transfusion products may bias the recipient immune system in a pro-inflammatory fashion.