Influence of stress on DDT-induced humoral immune responsiveness in mice

The effects of different durations/intensities of stress on DDT-induced modulation of humoral immune response were evaluated in mice. DDT (20, 50, or 100 ppm x 4 weeks) per se did not influence the primary antibody response to sheep red blood cells (SRBC). However, when DDT-pretreated mice were exposed to single and multiple sessions of restraint stress (RS), the anti-SRBC antibody titers were lower than the control values, the most prominent effects being seen after 50 and 100 ppm DDT exposure in combination with a single intense stressor (24 hr RS) or repeated stress (1 hr RS x 5). In the splenic plaque forming cells (PFC) assay, similar potentiations of DDT-induced immune suppression were seen at 50 and 100 ppm exposure levels in combination with 24 hr RS or 1 hr RS (x5) procedures. In addition, the 20 ppm DDT exposure effect was also potentiated in combination with the multiple RS model. Further, other forms of stress viz. 3 hr cold restraint stress (CRS) or 6 hr RS, which per se did not influence the antibody titer or PFC response, suppressed humoral immune responses, when combined with 100 ppm DDT exposure. These results are discussed in light of the possible interactions between physical/emotional and environmental/xenobiotic stressors in the regulation of humoral immune response.