Expression of CD14 and CD44 on bovine polymorphonuclear leukocytes during resolution of mammary inflammatory response induced by muramyldipeptide and lipopolysaccharide

The aim of the study was to prove the effect of muramyldipeptide and lipopolysaccharide on the expression of CD14 and CD44 during an induced inflammatory response of the mammary gland and its resolution. The purpose was to clarify whether the CD14 and CD44 expression is controlled by the mechanisms of resolution. The CD44 had previously been judged to be an activation marker along with CD11b on polymorphonuclear leukocytes. The experimental inflammatory response was induced by muramyldipeptide and lipopolysaccharide, while phosphate buffered saline was used as a control. The course of the inflammatory response was monitored at four time points: 24 h and 48 h (initiation of inflammatory response), 72 h and 168 h (resolution of inflammatory response). The total number of cells was determined by a hemocytometer. Flow cytometry was used to determine differential counts of leukocytes, proportions of CD11b+ polymorphonuclear leukocytes, proportions of apoptotic and necrotic polymorphonuclear leukocytes, and proportions of CD14+ and CD44+ polymorphonuclear leukocytes. The proportion of CD11b+ polymorphonuclear leukocytes after induction of inflammation with muramyldipeptide was higher (<I>P</I> < 0.05) compared to that after induction by phosphate buffered saline, was highly significantly greater after lipopolysaccharide (<I>P</I> < 0.01), and remained at approximately the same level for the whole period of observation (168 h). A higher proportion of CD14+ polymorphonuclear leukocytes was observed 72 h after induction with phosphate buffered saline. A statistically highly significant lower proportion was observed after induction with muramyldipeptide (<I>P</I> < 0.01), and a statistically significant lower proportion was observed after induction with lipopolysaccharide (<I>P</I> < 0.05). Decrease in the proportion of CD14+ polymorphonuclear leukocytes followed. In the initial phase of the inflammatory response (24 to 72 h) there was a gradual increase in the proportion of CD44+ polymorphonuclear leukocytes, and more so after the phosphate buffered saline. A greatly lower proportion of CD44+ polymorphonuclear leukocytes was observed after administration of muramyldipeptide and lipopolysaccharide: 24 h (<I>P</I> < 0.01), 48 h (<I>P</I> < 0.05) and 72 h (<I>P</I> < 0.01). Compared with muramyldipeptide and lipopolysaccharide, there was a statistically highly significant (<I>P</I> < 0.01) lower proportion of CD44+ polymorphonuclear leukocytes observed 168 h after induction with phosphate buffered saline. Hence the proportion of CD44+ polymorphonuclear leukocytes is low in the initial phase of inflammation, and CD44, in contrast with CD11b, does not appear to be a polymorphonuclear marker of activation. The results of the study have shown that expression of CD14 and CD44 is controlled by the factors inducing inflammatory response as well as by the mechanisms of resolution.