Induction of surface antigen CD69 expression in T-lymphocytes following exposure to actinomycin D

The expression of surface antigen CD69 in immune response cells is typicall y associated with the early stage(s) of cell activation, with maximal expre ssion levels within 4 h of appropriate antigenic or mitogenic stimulation, and maintenance of these high expression levels for 18-24 h. The expression profiles of CD69 in human peripheral blood mononuclear cells (PBMC)culture d with actinomycin D prior to mitogenic stimulation were evaluated by direc t immunofluorescence using flow cytometry. Pretreatment of PBMC suspensions with low, non-toxic levels of actinomycin D stimulated CD3(+) T-lymphocyte s to express CD69 in a concentration-dependent manner. Furthermore, CD4(+) T-lymphocytes were the primary cells responding in this fashion. Secondary mitogenic stimulation following antibiotic treatment potentiated cellular C D69 expression in these assays. CD69 expression was profoundly suppressed w ith in vitro actinomycin D concentrations greater than or equal to 1-2 mu g /ml, presumably by interference with cellular transcription/translation mec hanisms. Parallel thymidine incorporation assays indicated that actinomycin D effectively inhibited thymidine uptake in a concentration-dependent mann er, with complete inhibition at greater than or equal to 0.1 mu g/ml. The e valuation of cell cycling dynamics following antibiotic treatment, with and without secondary mitogen stimulation, indicated no substantial changes in DNA synthesis over controls. The diversity of these responses suggests tha t expression of CD69 may not solely reflect mitogenic activation status but may, under some conditions, result from induced cellular stress. (C) 1999 International Society for Immunopharmacology. Published by Elsevier Science Ltd. All rights reserved.