The effects of dexamethasone, betamethasone, flunixin and phenylbutazone on bovine natural-killer-cell cytotoxicity.

A series of in-vitro experiments was performed utilizing the ability of bovine peripheral-blood mononuclear cells (PBMC) to induce lysis of Madin-Darby bovine kidney (MDBK) cells infected with bovine herpesvirus 1 (BHV1), in an antibody-independent natural-killer(NK)-cell cytotoxic assay. The effects of dexamethasone (dexamethasone sodium phosphate), betamethasone (betamethasone sodium phosphate), flunixin (flunixin meglumine) and phenylbutazone on this NK cytolysis were studied using concentrations of the drugs ranging from well below to well above those normally attained in plasma at recommended therapeutic doses. All four drugs inhibited NK activity. For each agent a minimum inhibitory concentration (MIC50) required to inhibit NK activity by approximately 50% was calculated. For dexamethasone, betamethasone and flunixin the MIC50 was lower after a 24-h pre-incubation of PBMC with each drug, although a marked inhibition was seen when the drug was only present during the 5-h NK assay itself. In contrast the MIC50 for phenylbutazone rose after a 24-h pre-incubation with PBMC.