DIRECT EFFECTS OF 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN (TCDD) ON RESPONSES TO LIPOPOLYSACCHARIDE (LPS) BY ISOLATED MURINE B-CELLS

Previous results from this laboratory have indicated that the B-cell i s the Primary cell target responsible for the suppression of humoral i mmunity by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). While other lab oratories have confirmed that the B-cell is affected, there is not a c lear understanding of TCDD's relative effects on B-cell proliferation and differentiation. In the present study, we isolated B-cells from wh ole spleen cell suspensions from female B6C3F1 mice and further separa ted them according to density on a percoll density step gradient. Cell cycle analysis by propidium iodide indicated that both high (i.e., 1. 092-1.079 density interface) and low (i.e., 1.079-1.070 density interf ace) density B-cells were predominantly cells in the G0/G1 phase of th e cell cycle. Based on acridine orange staining, low-density B-cells e xhibited slightly higher RNA levels than high-density B-cells indicati ng they are an ''activated'' population of cells, probably somewhere i n G1A. Confirmation of these results was the observation that the high density, small, resting B-cells had negligible background proliferati on and immunoglobulin secretion, while the low density, larger, activa ted B-cells had marked background proliferative and antibody responses . Direct addition of TCDD (0.3-30.0 nM) produced a significant, dose-r elated and comparable suppression of both parameters in the low densit y B-cells. Similar results were obtained when low density B-cells were stimulated with LPS and exposed to TCDD. In contrast, neither the pro liferation nor the antibody response by high density B-cells stimulate d with LPS were affected by TCDD. These findings demonstrate that low density splenic B-cells are targets in suppression of antibody respons es by TCDD, and that both proliferation and differentiation are coordi nately affected.