COMPLEMENT COMPONENT C3B AND IMMUNOGLOBULIN FC-RECEPTORS ON NEUTROPHILS FROM CALVES WITH LEUKOCYTE ADHESION DEFICIENCY

Receptors for opsonins, such as complement component C3b (CR1) and imm unoglobulins, Fc receptors, interact with adhesion glycoproteins in me diating immune functions. Defects in expression of the adhesion glycop roteins CD11/CD18 results in severely hampered in vitro and in vivo ad herence-related functions of leukocytes. Little is known regarding the effect of leukocyte adhesion deficiency (LAD) on ligand binding and r eceptor expression. We investigated the binding and expression of CR1 and Fc receptors by bovine neutrophils isolated from dairy calves suff ering from LAD, compared with clinically normal (hereafter referred to as normal) age-matched calves. Neutrophils were also assayed for endo genously bound IgG and IgM and for exogenous binding of C3b, IgG(1), I gG(2), IgM, and aggregated IgG (aIgG), using flow cytometry. Luminol-e nhanced chemiluminescence (CL) production in response to IgG(2) opsoni zed zymosan was studied, and specific inhibition of ct was used to det ermine the specificity of IgG(2) binding. Activation of protein kinase C with phorbol myristate acetate was used to determine the effect of cellular activation on expression of CR1. A greater percentage of neut rophils from normal calves bound C3b than did neutrophils from LAD-aff ected calves. Receptor expression was similar. Activation with phorbol myristate acetate resulted in increased expression of CR1 on neutroph ils from normal and LAD-affected calves, but expression was almost two fold greater on neutrophils from normal calves. There was no differenc e between LAD-affected and normal calves in percentage of neutrophils that bound endogenous IgG and IgM. A greater percent age of neutrophil s from normal calves bound exogenous IgM than did neutrophils from LAD -affected calves. Receptor expression for aIgG was greater on neutroph ils from LAD-affected calves than on those from normal calves. Luminol -enhanced ct of neutrophils in response to IgG(2) opsonized zymosan wa s not different between LAD-affected and normal calves. Results indica te increased binding and expression of Fc receptors for aIgG and decre ased binding and expression for C3b and IgM on neutrophils from calves with LAD. Leukocyte adhesion deficiency may be compounded by added de fects in the expression and binding of receptors for opsonins, such as C3b and IgM.