PRBC suppresses mitogen-stimulated human and antigen-stimulated mouse T-cell proliferation by mechanisms independent of arginine depletion. This is a novel mechanism for transfusion-associated immune suppression.
Background
Transfusion of packed red blood cells (RBCs) produces a myriad of immunologic derangements, from suppressive to stimulatory. Proliferation of human T cells is suppressed in vitro after exposure to processed red blood cells (PRBCs). We hypothesized that this effect would be mitigated by using fresh RBCs. We also hypothesized that this suppressive effect was a generalized effect on lymphocyte proliferation and would be observed in both CD4+ and CD8+ T-cell subpopulations as well as B cells.
Materials and methods
We isolated human T cells from donor peripheral blood mononuclear cells and exposed them to either blood bank PRBCs or fresh RBCs from volunteer donors and stimulated them with anti-CD3/anti-CD28. Human B cells were stimulated with lipopolysaccharide and exposed to PRBCs or fresh RBCs. We measured proliferation of B cells by thymidine incorporation assays. We also treated RBCs with citrate-phosphate-dextrose (CPD) at different time points before culture them with stimulated T cells to determine the role of this common RBC storage solution in lymphocyte proliferation.
Results
In vitro proliferation of CD4+ and CD8+ T cells was suppressed by blood bank RBCs. This suppression is eliminated when fresh RBCs were used. The B cells showed inhibition of proliferation when exposed to similar conditions, which appeared to be consistent over serial dilutions. Fresh RBCs exposed to CPD did not appear suppressive in the first 6 h after exposure.
Conclusions
T-cell and B-cell proliferation inhibition by blood banked RBCs suggests a generalized effect of RBCs on cellular proliferation. The lack of suppression by fresh RBCs further suggests that something involved in blood banking alters RBC properties such that they attain a suppressive phenotype. One such blood banking component, CPD, does not appear to affect this suppressive phenotype within the first 6 h.
Background
Packed red blood cells (PRBC) suppress T cell responsiveness through a mechanism requiring cell-cell contact. Questions remain as to whether this effect is an allogeneic response, related to cell death, or dependent on particular components of the red blood cells.
Study Design and Methods
Peripheral T cells were isolated from healthy donors and exposed to stored allogeneic PRBC or autologous red blood cells after processing. Red blood cells were lysed by hypotonic solvent to produce cellular ghosts. Tritiated thymidine proliferation assays were utilized. Cultures were saturated with IL-2 to determine whether impaired IL-2 synthesis played a role.
Results
T cell proliferation was suppressed by both autologous and allogeneic PRBCs. PRBC membrane integrity does enhance T cell suppression. T-cell death is not responsible for the suppressive changes. IL-2 synthesis is suppressed in PRBC-exposed T cells but addition of exogenous IL-2 does not rescue proliferative capabilities. Proliferation of T cells was inhibited with PRBC exposure but mitigated with the addition of fresh RBC.
Conclusions
T cell suppression is enhanced by intact PRBC but this effect is unrelated solely to alloantigens. Neither apoptosis nor necrosis of T cells contributes to this phenomenon. IL-2 synthesis is suppressed after PRBC exposure as a consequence of T cell inhibition, but is not the primary cause of suppression. Fresh RBC do not mediate T cell suppression indicating that changes in the RBC and development of the storage lesion may occur during initial blood bank processing.
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