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 immunoglobulins, Fc receptors, interact with adhesion glycoproteins in mediating immune functions. Defects in expression of the adhesion glycoproteins CD11/CD18 results in severely hampered in vitro and in vivo adherence-related functions of leukocytes. Little is known regarding the effect of leukocyte adhesion deficiency (LAD) on ligand binding and receptor expression. We investigated the binding and expression of CR1 and Fc receptors by bovine neutrophils isolated from dairy calves suffering from LAD, compared with clinically normal (hereafter referred to as normal) age-matched calves. Neutrophils were also assayed for endogenously bound IgG and IgM and for exogenous binding of C3b, IgG1, IgG2, IgM, and aggregated IgG (aIgG), using flow cytometry. Luminol-enhanced chemiluminescence (CL) production in response to IgG2 opsonized zymosan was studied, and specific inhibition of CL was used to determine the specificity of IgG2 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 neutrophils from normal calves bound C3b than did neutrophils from LAD-affected calves. Receptor expression was similar. Activation with phorbol myristate acetate resulted in increased expression of CR1 on neutrophils from normal and LAD-affected calves, but expression was almost twofold greater on neutrophils from normal calves. There was no difference between LAD-affected and normal calves in percentage of neutrophils that bound endogenous IgG and IgM. A greater percentage of neutrophils from normal calves bound exogenous IgM than did neutrophils from LAD-affected calves. Receptor expression for aIgG was greater on neutrophils from LAD-affected calves than on those from normal calves. Luminol-enhanced CL of neutrophils in response to IgG2 opsonized zymosan was not different between LAD-affected and normal calves. Results indicate increased binding and expression of Fc receptors for aIgG and decreased binding and expression for C3b and IgM on neutrophils from calves with LAD. Leukocyte adhesion deficiency may be compounded by added defects in the expression and binding of receptors for opsonins, such as C3b and IgM.