The work outlined in this application lies at the intersection of two of our society's pressing problems, drug abuse and the AIDS pandemic. While the incidence of new AIDS cases has been declining among some of the traditional high risk groups the problem among intravenous drug users is worsening. There is evidence to indicate that opiates have the potential to suppress the immune system and, unfortunately, this fact may create a situation in which i.v. drug abusers are placing themselves in a biological, type of "double jeopardy." While the literature contains a number of reports which suggest that opiates are able to affect the functioning of the immune system, the mechanism by which morphine addiction alters the immune response is not clear. However, it seems that an opiate such as morphine may have a direct effect on the immune system or, alternatively, an indirect one. The indirect mechanism may involve altered levels of neuroendocrine hormones. There is evidence which suggests that opiates are able to affect the immune system through both direct and indirect mechanisms. The hypothesis which we plan to test is; "The profound immunosuppression observed following morphine administration to mice is not attributable to a single mechanism. Morphine's direct effects on immunologic cells are compounded by other immunosuppressive events which relate to morphine's actions in the brain. These indirectly immunosuppressive actions of morphine involve the hypothalamic-pituitary-adrenal (HPA) axis as well as the sympathetic nervous system (SNS)." To evaluate the validity of this hypothesis, the following specific aims are proposed: (1) Define the parameters of the thymic atrophy and humoral immune suppression observed in mice implanted with a morphine pellet. (2) Deter-mine the mechanisms which account for the marked in vivo thymic atrophy observed in mice treated with morphine. (3) Determine the mechanisms by which morphine causes in vivo suppression of the splenic humoral immune response to an injection of SRBC. To accomplish these aims a combination of in vitro and in vivo studies are planned. Experiments have been designed to better define the immune deficits which occur in morphine treated mice and to determine which cells of the immune system are most susceptible. The morphine susceptibility of primary relative to secondary immune responses will be examined. Flow cytometry will be used to identify the subpopulations of cells which are depleted from the spleen and thymus following morphine treatment. Studies to identify apoptosis as the mechanism by which morphine induces thymic atrophy are planned, as well experiments to assess the role of the HPA axis and SNS in initiating it. Experiments will be performed to determine the relative contribution of morphine's direct vs. it's indirect effects in the suppression of the antibody response in the spleen. Separation-reconstitution studies will identify the cell, or cells, in the antibody response which are functioning subnormally. Completion of the proposed experiments should contribute to an understanding of the direct and neuroimmune mechanisms through which morphine is able to suppress immunity.