Depression of colony formation by human thymus-derived lymphocytes with rifampin and other antimicrobial agents

Colonies of human lymphocytes with thymus-derived (T) cell characteristics can be induced in phytohemagglutinin-P to grow in a semisolid medium. To expand the data base on the effects of antimicrobial agents on cell-mediated immunity, the effect of 30 antimicrobial agents on T-lymphocyte cloning was studied. All of the drugs were added to the cultures in concentrations ranging from 10(-5) to 10(-14) M, and the results were compared with those in cultures without the drug. Drugs that inhibit protein synthesis at the 50S ribosomal subunit in bacteria--in particular, chloramphenicol, clindamycin, erythromycin, and troleandomycin--suppressed colony formation. However, the most significantly immunosuppressive agent was rifampin; it suppressed colony formation at concentrations of up to 2.5 x 10(-9) M, a value significantly lower than that found in previous in vitro testing and well below therapeutic levels. Screening of drugs by lymphocyte cloning techniques for possible suppression of cell-mediated immunity appears to be a rapid, sensitive, and inexpensive procedure.