Characterization of peripheral blood and pulmonary leukocyte function in healthy foals

Studies in infants and foals indicate an age-dependent maturation of periph eral lymphocyte subsets. The age-dependent relationship for maturation of c ellular immune responses, such as phagocytosis and lymphocyte responses of the peripheral and pulmonary-derived leukocytes, has not been characterized in foals, Lymphocyte subpopulations, mitogen stimulation response of lymph ocytes, lymphokine-activated killing cell activity, phagocytosis and oxidat ive burst activity, and serum immunoglobulin (Ig) classes G and M concentra tions were determined in developing foals, This study illustrates age-depen dent changes in immunoglobulin class concentrations, lymphocyte subsets, an d EqMHC Class II expression in cells of the peripheral blood and lungs of d eveloping neonatal-to-weanling foals. The increase in peripheral blood and BAL B-lymphocytes and serum immunoglobulins in developing foals suggests ex pansion of immune cell populations during a time in which environmental pat hogen exposure is great. General immune function, mitogenic responses, LAK cell activity, opsonized phagocytosis, and oxidative burst activity of newb orns was similar to the adult horse. Total immune-cell numbers, rather than function, seemed to be the limiting factor in the development of the equin e neonatal immune system. There was an age-related percent increase in the appearance of pulmonary lymphocytes, but a percent decrease in macrophages. Although development of the respiratory immune system follows changes in t he peripheral blood, cellular expansion, activation, and migration may occu r at a slower pace, making the respiratory environment susceptible to patho gens prior to optimal immune system maturity. (C) 2000 Elsevier Science B.V . All rights reserved.