CELLULAR ASPECTS OF OPIATE BINDING TO LEUKOCYTES

点击翻译按钮获取中文摘要

The role of exogenous morphine-based drugs and endogenous opioids, like B- endorphin, in the direct modulation of the human cellular immune system has potentially important consequences in infectious disease. Both illicit drug addiction and stress-induced release of B-endorphin have been cited as factors in elevated susceptibility to communicable diseases from the common cold to TB and AIDS. While the immunological effects of the exposure of immune cells to opiates are well known, little information has been obtained concerning the mechanism of action of morphine on immune cells. In the central nervous system, a family of G protein-coupled opiate receptors exist which account for the activity of a variety of opiates. The genes for these receptors have recently been cloned from both murine and human sources and their structure - that of a 7-transmembrane helical segment protein - deduced. However, when immune cells are screened by reverse transcriptase/polymerase chain reaction methods, only the delta and kappa receptors were found. The mu receptor (MOR), the primary high affinity morphine binding site in the CNS, is missing as judged by ligand binding assays and RT-PCR assays for expressed MOR mRNA. In fact, the only high affinity morphine binding site (POR) is found on phytohemagglutin activated T lymphocytes. (-)-Morphine can be displaced from this site by both (-)- and (+)-morphine and the N-terminal of B-endorphin, but not by DAGO, DADLE and U-50,488. Because this is the only reported, high affinity site for morphine on T lymphocytes, it is important to clone this site and determine whether it is present only on activated cell types or whether it is also present on nonactivated cells at levels below the detection threshold of the binding assays. Beside being inducible, it is possible that this site might also be expressed constituitively prior to induction and could function as the initial step in morphine's action on T lymphocytes. To test this hypothesis, POR will be cloned by homology with known opiate receptors using RT-PCR or by expression cloning. The POR clone will then be used to investigate lymphocyte populations isolated by magnetic bead/antibody complexation based on their state of activation. The activation state of the lymphocytes will also be modified by specific mitogen stimulation. The results of these experiments will answer 2 important question of immunopharmacology - 1. Is the inducible morphine binding site (POR) sufficient to explain the action of morphine on the cellular immune system?; and 2. What is the correlation between expression of the induced binding site and the activation state of the T cell subtype?. Ultimately, to control the effects of opiates on the immune system, it is necessary to understand the mechanisms by which opiates modulate the cellular immune system. Currently, there is a major gap in our knowledge about opiate mechanisms in the immune system which the proposed experiments would close.