Haemorrhage produces depressions in alloantigen-specific immune responses in the mouse through activation of suppressor T cells.

The development of cell-mediated and humoral immune responses in BALB/c mice (H-2d) directed toward El4 cells (H-2b) was suppressed (cell-mediated cytotoxicity, 40-50% of control; antibody titres 127 +/- 17 versus 287 +/- 17 in controls) following haemorrhage of 30% total blood volume. This haemorrhage-induced depression of immune response can be transferred to normal recipients with T cells (3 x 10(7] from haemorrhaged syngeneic donors. Flow microfluorimetry (FMF) analysis showed no shift in CD8:CD4 ratios following haemorrhage. These results suggest that haemorrhage suppresses immune response through activation of suppressor T cells.