Evaluation of the role of endotoxin and cortisol on modulation of CD18 adhesion receptors in cows with mastitis caused by Escherichia coli

Objective-To determine the effect of mastitis caused by Escherichia coil on expression of CD18 cell surface receptors and to evaluate the involvement. and regulation of receptors by lipopolysaccharide (LPS) and cortisol. Animals-11 clinically normal lactating Holstein-Friesian cows. Procedure-Binding of CD18 monoclonal antibodies to neutrophils was studied, using flow cytometry, before and after intramammary inoculation of E coil organisms. Effect of LPS and cortisol on expression of adhesion receptors w as investigated, using a whole-blood model. Results-Expression of CD18 adhesion receptors on bovine neutrophils increas ed 35% by 12 hours after intramammary inoculation of E coli By 24 hours aft er inoculation, the number of receptors had returned to control values. Hig h cortisol concentrations (100 nmol/L) were seen 12 to 18 hours after inocu lation. Addition of LPS to blood induced a 30% increase in the number of CD 18 receptors, and maximal number of receptors was expressed at an LPS conce ntration of 0.1 ng/ml, A decrease in the number of CD18 receptors was induc ed by incubation with cortisol or dexamethasone before challenge-exposure w ith LPS. Conclusions-An increase in the number of CD18 receptors on neutrophils is m ediated by local production of LPS, Subsequent endogenous release of cortis ol may prevent additional increases in the number of receptors. Clinical Relevance-During acute mastitis caused by E coli, there is an incr ease in the number of CD18 receptors on circulating neutrophils. Cortisol i nduces a decrease in the number of CD18 receptors, probably modulating the acute inflammatory response in mammary glands of lactating cows.