Splenic macrophages and B cells mediate immunosuppression following abrupt withdrawal from morphine

We have previously shown that abrupt withdrawal (AW) from morphine induces greater than 80% immunosuppression in murine spleen cells, as assessed by the capacity to mount an in vitro plaque-forming cell response to sheep red blood cells. Present studies about the mechanisms of immunosuppression following AW showed that addition of highly enriched (CD11b+) splenic macrophages (obtained by cell sorting or magnetic separation) from AW mice to cultures of normal, unfractionated spleen cells suppressed immune responses. Further, addition of highly enriched (CD19+) B cells (but not T cells) from AW mice to normal cells was also immunosuppressive. B cells from AW mice were also able to inhibit the proliferative response of normal spleen cells to concanavalin A but not to lipopolysaccharide. Overall, the data suggest that immunosuppression by AW spleen cells is a result of active suppression by macrophages and B cells.