Effect of hydrocortisone on the response of rat lymphocytes to phytohaemagglutinin

Lymphoproliferative response to mitogen (ConA) after treatment of rats with gentamicin and doxycyclin: relevance to human therapeutics

Interaction of xenobiotics with the immune system may result in undesirable effects such as immunosuppression. In the future, it is probable that immunological screening tests may be required for safety evaluation of new drug candidates as an adjunct to more traditional toxicity testing. The lymphoproliferative response to mitogens has been proposed as a screening test. This test has been set up and validated in mice, but will probably have to be done in rats, the species of choice for drug safety studies. This test has been adapted to rats, using both in vivo and in vitro treatments, and used to validate drugs, including doxycyclin and gentamicin (with cyclosporin A and hydroxycortisone as controls) at the dose levels used in toxicology studies. Discrepant results obtained with doxycyclin and hydroxycortisone (effect in vitro but not in vivo) suggest that further validation studies are necessary in order to assess the reliability of this test.

Effect of corticosteroid on porcine leukocytes: age-related effects of corticosteroid inhibition on porcine lymphocyte responses to mitogens

The effects of prednisolone sodium succinate on the responses of porcine lymphocytes to phytohemagglutinin (PHA) and pokeweed mitogen (PWM) were investigated. Sensitivity of peripheral blood lymphocytes (PBL) to the synthetic glucocorticoid, prednisolone, was related to age of the lymphocyte donor. The greatest sensitivity was found in PBL from animals less than one week old; PBL from animals between 2 to 4 months retained some glucocorticoid sensitive cells; whereas, PBL from animals older than 6 months were exceptionally resistant to steroid. Similar age-associated sensitivities were found for lymphocytes from lymph node, spleen and thymus. Significant differential sensitivities among the various lymphoid organs were found with the thymic lymphocyte possessing the greatest sensitivity to steroid and the PBL lymph node and splenic lymphocytes possessing the highest resistance to the suppressive effects of steroid. The age related differences in sensitivity to steroid did not appear to be caused by differences in the number of steroid receptors because lymphocytes from susceptible and resistant animals had similar numbers of receptors. The results suggest that the age related sensitivity may be associated with a higher percentage of sensitive thymic-derived lymphocyte in the PBL, lymph node and spleen of the younger animals. Results of this study also suggest that the adult pig (6 months) should be classified as a steroid resistant species.

Acetylspiramycin and the immune system--II. Effects on lymphocyte proliferation, lymphokine production, delayed-type hypersensitivity and antibody production

The effects of the antibiotic acetylspiramycin (ASPM) on lymphocyte function were studied in vitro and in vivo. When added to lymphocyte cultures in vitro, ASPM inhibited splenic lymphocyte transformation induced by phytohemagglutinin (PHA), lipopolysaccharide (LPS) and antigen. It also depressed production by spleen cells of the lymphokine inducing procoagulant activity in mouse macrophages. Spleen cells from mice given ASPM orally showed enhanced responses to PHA, but normal responses to LPS. The capacity to produce lymphokine was increased early after oral ASPM and slightly decreased after prolonged administration. Oral ASPM had no effect on the production of antibodies and a very slight enhancing effect on the development of delayed-type hypersensitivity to sheep red blood cells.

The differential sensitivity of rat peripheral blood T cells to immunosuppressants: cyclophosphamide and dexamethasone

Peripheral blood T cells from rats given a single oral dose of dexamethasone (DMS) or cyclophosphamide (CY) exhibited a differential sensitivity to these compounds as measured by lymphoproliferation in the presence of concanavalin A (Con A) or phytohemagglutinin hemagglutinin (PHA). Con A-responsive cells (T Con A) were found to be resistant to the effects of DMS, while the PHA-responsive population (T PHA) showed a dose-dependent suppression at dose levels of 0.35 and 1.00 mg/kg. DMS did not alter serum antibody production against sheep erythrocytes at the dosage level which produced a significant depression of the PHA response. Animals treated with CY showed enhanced Con A-mediated lymphoproliferation at a dose of 15 mg/kg and marked suppression at 45 mg/kg. The PHA-mediated response, however, exhibited only a dose-dependent suppression at both dosage levels. CY had no effect on the antibody response at doses that enhance Con A lymphoproliferation. These results suggest that T helper cells and T suppressor cells are not TpHA cells.