In vivo and in vitro effects of doxycycline on leucocyte membrane receptors

Tetracyclines, particularly doxycycline, have adverse effects on granulocyte function in vitro. We have examined the effects of doxycycline on membrane receptors for IgG (Fc gamma-R) and C3b (C3b-R) on granulocytes and lymphocytes, as well as on the sheep erythrocyte receptor (E-R) on T lymphocytes. Acne patients given doxycycline orally had a lower percentage of Fc gamma-R positive granulocytes (57%) than before treatment (80%) or compared to healthy controls (81%). Following in vitro doxycycline incubation, normal granulocytes showed decreased levels of Fc gamma-R positive cells. This effect was counteracted by the addition of magnesium during incubation. The deleterious effect of doxycycline on granulocyte functions may be due to decreased levels of Fc gamma-R bearing granulocytes. Doxycycline in vivo or in vitro had no significant effect on the proportion of C3b-R bearing granulocytes or lymphocytes or the T lymphocyte percentage. After in vitro irradiation with light at 340-380 nm, however, both granulocytes and lymphocytes preincubated with doxycycline showed up to 50% decrease in Fc gamma-R bearing cells, while control cells without doxycycline were unaffected.