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The effects of minocycline and tetracycline on the mitotic response of human peripheral blood lymphocytes was investigated in vitro. The effects of the antibiotics on the mitotic response of purified lymphocytes stimulated with Interleukin-1 beta varied according to the individual from whom the lymphocytes were obtained. At concentrations above those reported to be present in serum during conventional therapy (2-8 mg/l), there was a tendency for both minocycline and tetracycline to suppress the mitotic response. Minocycline was superior to tetracycline in this respect. However, at physiological concentrations the antibiotics either had no significant effect, suppressed the mitotic response (minocycline at 2 mg/l with one of six donors), or enhanced the mitotic response (tetracycline at 2 and 8 mg/l with four of six donors). The stimulatory effect of tetracycline was not demonstrated when lymphocytes were cultured in whole blood for up to seven days with the antibiotic alone. Similar effects of the antibiotics were observed when mononuclear cell fractions isolated from six donors were stimulated with an optimal concentration of phytohaemagglutinin (PHA). Stimulation of lymphocytes in whole blood cultures with PHA in the presence of minocycline and tetracycline revealed that, under these culture conditions, the antibiotics could suppress the mitotic response of lymphocytes at physiological doses with cells from a majority of donors.
Ingham et al. (Tue,) studied this question.