title: Inhibition by colchicine of human lymphocytotoxic function: dependence on cell-bound drug level, spontaneous reversibility and antagonism by desacetylcolchicine (DAC).
abstract: Colchicine elicits inhibition of spontaneous, PHA-dependent and antibody-dependent forms of lymphocytotoxicity of peripheral blood lymphocytes (PBL) against allogeneic target cells. The findings are that it does so in cell-bound form and to near-maximum effect in the amount of this produced in PBL exposed to it at 10(-6)M concentration for 2 h at 37 degrees C. This represents only a small fraction of the cells' binding capacity, which suggests that it involves sites special in kind (localisation) rather than number (occupied at random). Desacetylcolchicine (DAC) (a known inhibitor of the colchicine-tubulin binding reaction) afforded the PBL protection at concentrations that antagonised the binding of colchicine to them. That DAC itself hardly inhibited PBL function is attributed by inference to a weaker binding affinity making for readier loss of it upon removal of the free drug. It did, however, exhibit a tight form of binding to other, functionally-insensitive cell sites not competed for by colchicine at 100-fold higher concentration. Contrary to the impression lent by other workers' studies (on mouse lymphocytes), colchicine-induced suppression of cytotoxic function is not necessarily irreversible. PBL cultured in drug-free medium gradually lost bound colchicine and they recovered in capacity to express spontaneous and PHA-dependent activity, but not in antibody-dependent activity. The residual cytolytic activity shown by colchicine pre-treated PBL appears in the case of antibody-dependent activity to be truly colchicine resistant; it survived unchanged a 10-fold increase in cell-bound drug level and it cannot be explained as a possible product of recovery. This colchicine-independence may reflect the existence of tubulin/microtubule-independent mechanisms contributing to antibody-dependent activity. Examination of colchicine-treated PBL for membrane fluidity changes, using the probe molecule DPH and the technique of fluorescence polarisation, has yielded negative results, even for cells treated at excessively high colchicine concentration (10(-4)M). All three forms of lymphocytotoxic activity were retained in PBL reconstituted after cryopreservation in liquid nitrogen.
mesh_terms: D000920:Antibody-Dependent Cell Cytotoxicity / Q000187:drug effects; D003078:Colchicine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D003602:Cytotoxicity, Immunologic / Q000187:drug effects*; D004161:Diphenylhexatriene / Q000494:pharmacology; D005260:Female; D006801:Humans; D008214:Lymphocytes / Q000187:drug effects / Q000276:immunology* / Q000528:radiation effects; D008297:Male; D008560:Membrane Fluidity; D010835:Phytohemagglutinins / Q000494:pharmacology
chemical_list: D010835:Phytohemagglutinins; D004161:Diphenylhexatriene; C003707:trimethylcolchicinic acid methyl ether; D003078:Colchicine