FC RECEPTOR EXPRESSION, CONCANAVALIN-A CAPPING, AND ENZYME CONTENT OF BOVINE NEONATAL NEUTROPHILS - A COMPARATIVE-STUDY WITH ADULT CATTLE

The increased susceptibility of newborns to infection may in part be related to impaired in vitro functions of neonatal polymorphonuclear neutrophils (PMNs). To evaluate early steps in the activation cycle of bovine PMNs we determined the expression of Fc receptors (FcRs) with an erythrocyte rosetting assay utilizing bovine anti-sheep immunoglobulin G2 IgG2 and the accumulation of ligand receptor complexes or "caps" with fluorochrome-coupled concanavalin A (Con A caps) on neutrophils from adult (A-PMN) and newborn (N-PMN) bovines. In addition, the levels of myeloperoxidase (MPO) and alkaline phosphatase (AP) were determined. FcR expression is reduced in N-PMNs (P < .001), in contrast to results observed with human N-PMNs. Basal capping of Con A binding sites is reduced (P < .05) in N-PMNs but is enhanced (P < .001) upon pretreatment with colchicine (0.5, 5.0, and 50.0 mum). These findings are again contrary to results observed with human N-PMNs. Consistent with findings in human neonates, however, are reduced levels of cellular MPO (P < .05) and elevated cellular AP (P < .001) in the neonate. The functional significance of elevated AP levels and altered Con A capping in N-PMNs is unclear. However, diminished expression of FcR could potentially contribute to impaired adherence and phagocytosis of bacteria, and reduced activity of neutrophil MPO could indicate weaker microbicidal capacity of neonatal cells. The demonstrated impairment of N-PMN functions could potentially contribute to reducing the effectiveness of the cellular host defense system in neonatal calves.