STRESS-INDUCED REDUCTION IN THE RAT MIXED LYMPHOCYTE-REACTION IS DUE TO MACROPHAGES AND NOT TO CHANGES IN T-CELL PHENOTYPES

Exposure to aversive events or stressors modulates various aspects of immune function. We have previously reported that exposure to an acute stressor, inescapable tail shock (IS), resulted in a shift in T cell subpopulations in rat mesenteric lymph nodes but not in cervical lymph nodes (Fleshner et al. (1992) J. Neuroimmunol. 41, 131-142). The mese nteric CD4(+)/CD8(+) ratio was increased immediately after exposure to IS and was due primarily to an increase in the percent of CD4(+) cell s. The present experiments were designed to determine the relationship between the IS-associated phenotypic shift and its significance in th e function of CD4(+) T cells. The function assessed was the in vitro p roliferative response to alloantigens coded for by the Major Histocomp atibility Complex (MHC). Using the mixed lymphocyte reaction (MLR), we report that exposure to IS resulted in a decrease in the MLR response of cells from both cervical and mesenteric lymph nodes. Depletion of macrophages (nylon wool adherent cells) eliminated the IS-induced redu ction and co-culture of macrophages (irradiation-insensitive cells) fr om shocked rats produced the suppression. One interpretation of these data is that exposure to IS resulted in the activation of macrophages and the release of a suppressive factor which reduced the MLR response of peripheral lymph node lymphocytes.