Some tetracycline drugs suppress mitogen-stimulated lymphocyte growth but others do not

Eight tetracycline drugs were tested for inhibitory effect on phytohaemagglutinin (PHA) stimulated growth (measured by [3H]-TdR uptake) of peripheral blood mononuclear cells: at least 26 normal subjects were tested with each drug. Doxycycline reduced DNA synthesis appreciably at concentrations within and just above the therapeutic range of blood levels: it was the most potent inhibitor, but demeclocycline, methacycline and minocycline had similar, if less potent, effects. Tetracycline, oxytetracycline, chlortetracycline and clomocycline did not inhibit DNA synthesis of 3-day cultures even at concentrations five to ten times greater than the therapeutic blood level. Volume spectroscopy measurements showed that none of the eight tetracycline drugs interfered with the recruitment of cells into G1-phase growth of the first cell cycle after PHA stimulation.