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Haemorrhage‐induced alterations in function and cytokine production of T cells and T cell subpopulations

Haemorrhage produces alterations in macrophage, T and B cell function. In order to better define the mechanism for the effects of blood loss on immune response, we examined function of and cytokine production by purified T cells, CD4+ and CD8+ subpopulations after blood loss. Whereas T and CD4+ cells from control, unhaemorrhaged animals produced no alteration in proliferation when added to cultures of mitogen‐stimulated splenocytes from normal mice, proliferation was decreased when T or CD4+ cells from haemorrhaged mice were included. The addition of CD8+ cells from haemorrhaged animals to mitogen‐stimulated cultures reduced proliferation by approximately 50% more than that found when CD8+ cells from control, unhaemorrhaged animals were included. Supernatants of mitogen‐stimulated splenocytes from haemorrhaged mice contained significantly less IL‐2 and interferon‐gamma (IFN‐γ) than did those from control, unhaemorrhaged mice. CD4+ populations from haemorrhaged mice produced significantly more IL‐10, and significantly less IFN‐γ, than did CD4+ cells from control, unhaemorrhaged mice. There were no significant differences in IL‐2, IL‐4, IL‐10 or IFN‐γ production by CD8+ cells from haemorrhaged or control mice. The present experiments demonstrate that haemorrhage affects both CD4+ and CD8+ T cell subsets. In particular, haemorrhage appeared to activate CD4+, Th2 cells, with concomitant suppression of the Thl subpopulation. These results provide a mechanism which may contribute to the alterations in cytokine production previously described to occur following blood loss.