Effect of doxycycline on immune response in mice.

The effect of doxycycline on immune response has been studied in mice, cell-mediated immunity being evaluated with the split heart allograft technique. Survival duration of heart transplants in animals treated with 2.5 mg of doxycycline per kg per day from the day of transplantation until rejection was slightly but significantly longer than in untreated animals, 18.8 days (P less than 0.05) as compared with 14.5 days. In doxycycline-treated animals, both agglutinating and hemolytic antibody response to sheep erythrocytes was slightly but significantly decreased, though there was no inhibition of splenic production of antibodies to sheep erythrocytes (as measured by the number of plaques of hemolysis detected). The results show the immune response in mice to be only moderately inhibited by doxycycline. The relevance of experiments in mice is also discussed.

Antibiotic accumulation in human polymorphonuclear leucocytes and lymphocytes.

Human polymorphonuclear leucocytes and lymphocytes were incubated with 10 different radiolabelled antibiotics (10 micrograms/ml) for 2 hours. The ratio of cellular concentration to extracellular concentration of the drugs was determined after centrifugation. For beta-lactam antibiotics and gentamicin the ratios were less than 1.0. The ratios for doxycycline, erythromycin, fusidic acid and rifampicin were 13, 4.3, 7-10 and 2.5 respectively indicating a cellular accumulation of these drugs. Erythromycin, fusidic acid and rifampicin were rapidly released from the cells in antibiotic free medium, while doxycycline was partly irreversibly bound.

Effect of fusidic acid on the immune response in mice.

The effect of fusidic acid on the immune response in mice was studied. At the nontoxic dose of 500 mg/kg per day, the cell-mediated immunity was strongly inhibited. A marked and significant prolonged survival of split-heart allografts in treated animals was detected. The survival time of allografts in mice receiving fusidic acid from the day of the transplantation until the grafts were rejected was 26.1 days compared with 14.5 days in untreated animals. In mice treated also before the transplantation, the mean survival of the allografts were even longer. The phytohemagglutinin response, as well as the mixed lymphocyte culture stimulation of spleen lymphocytes from mice given 500 mg of fusidic acid per kg daily for 1 week, were significantly inhibited. At the same dose there was also a significantly decreased primary antibody response to sheep erythrocytes, but it was of limited biological significance. The immunosuppressive effect in animals treated with a human therapeutic dose of fusidic acid (25 mg/kg per day) was less pronounced but significant. The relevance of these results is discussed.

Effect of rifampin on the immune response in mice.

In an investigation of the effect of rifampin on the immune response in mice, the cellular immunity was evaluated with the split-heart allograft technique. The survival time of the heart in animals treated with rifampin at a dose of 20 mg/kg per day from the day of the transplantation until the graft was rejected was longer (33.7 days, P less than 0.001) than that of animals not treated with antibiotics (14.5 days). When rifampin was given at a dose of 5 mg/kg per day for the same period, the mean survival time of allografts was 19.5 days. The number of demonstrable plaques of hemolysis and the humoral antibodies to sheep erythrocytes were also reduced by a human therapeutic dose (20 mg/kg per day). However, the suppression of the humoral immune response was probably of more limited biological significane, suggesting a differential sensitivity to rifampin. In contrast to rifampin, benzylpenicillin had no noteworthy inhibiting effect on the cellular or humoral immune response.

Antibiotic-host defence interactions in vitro and in vivo.

A markedly depressed chemotaxis was detected with an agarose gel technique when human leucocytes were incubated with fusidic acid and rifampicin in clinically obtainable concentrations. At high concentrations of newer well absorbed tetracyclines there was a definite depression and a less pronounced inhibition was detected for classical tetracycline. The incorporation of 14C-leucine into a trichloroacetic-acid insoluble form by human neutrophils was markedly depressed by the same antibiotics and it is suggested that some antibiotics acting by inhibition of protein synthesis also affect chemotaxis of human neutrophils. At therapeutic concentrations fusidic acid and rifampicin had a pronounced inhibiting effect on the incorporation of 3H-thymidine by human T-lymphocytes stimulated by PHA and B-lymphocytes by S. aurens, Cowan I. At concentrations above the therapeutic level inhibition was detected for doxycycline, erythromycin, clindamycin and nitrofurantoin. No apparent inhibition of neither chemotaxis by human neutrophils nor thymidine incorporation by lymphocytes could be detected for penicillins, cephalosporins, nalidixic acid, sulfamethoxazole and trimethoprim. Due to high albumin binding for some of the tested antibiotics and other factors involved, experiments were performed to test whether depression also takes place in vivo. The cellular immunity in mice was registered by monitoring the survival of transplanted heart grafts and the humoral immunity by quantitating plaque-forming cells and by titration of antibodies after immunization with sheep erythrocytes. Fusidic acid (500 mg/kg/day) and rifampicin (20 mg/kg/day, human therapeutic dose) had a highly significant effect (P less than 0.001) on the rejection of heart grafts and plaque-forming cells while the effect o serum antibodies was of low significance (P less than 0.02--P less than 0.01). The effect of doxycycline (2.5 mg/kg/day) and fusidic acid (25 mg/kg/day) at human therapeutic dose on immunity in mice was slight but significant (P less than 0.02). The relevance of experiments in mice to the situation in man is discussed. The migration of neutrophils into a skin chamber was shown to be dramatically reduced in eight healthy volunteers during a standard regimen of doxycycline.