Abrogation of graft-versus-host reaction by dieldrin in mice

Sublethal exposure to the organochlorine pesticide, dieldrin, decreased the T-cell immune response in mice. Indeed, a transient inhibition of the mixed lymphocyte reactivity (MLR) was noted at 7 days after intraperitoneal exposure to 0.6 LD50 dieldrin. The present study was undertaken to further investigate the effects of dieldrin on the T-cell immune response, using the graft-versus-host reaction (GVHR) as a model, in order to assess T-cell subset efficiency. Lymphoid cells of A/J mice injected intraperitoneally 7 days earlier with 36 mg/kg body weight dieldrin were transferred into H-2-incompatible F1 hybrids. With this model, known to induce a marked GVHR, we have observed that dieldrin inhibited the potential of parental cells to induce a GVHR in hybrid mice. This effect could not be attributed to a direct cell cytotoxicity, nor to the modulation of major T-cell subsets as shown by thymic and peripheral T-cell subpopulation analysis. Collaboration processes between these cellular subsets seem to represent a potential site for the dieldrin-induced suppression.