A gene controlling macrophage functional activation is linked to the chicken B‐complex

F2 segregants were produced and analyzed between two different pairs of parental B‐congenic chicken lines known to differ in macrophage functional capacity. Segregants involving crosses of lines 15.7‐B2 and 15.I5I‐B5 and of lines 15I5‐B15 and 15.N‐B21 were compared for in vitro chemotactic activity of mononuclear leukocytes and in vivo functional activation of elicited macrophages with lipopolysaccharide (LPS). As in parental lines, B2 B2 homozygotes produced mononuclear leukocytes which were inferior to B5B5 cells in chemotaxis but had elicited peritoneal macrophages which were elevated in induced phagocytic capacity for SRBCs. In general, B2 B5 heterozygotic macrophages had intermediate response levels compared with homozygotes. Similarly, B15B15 mononuclear leukocytes were lower in chemotactic activity to one of two chemoattractants tested while LPS‐elicited macrophages displayed higher phagocytic capabilities than did their B21B21 counterparts. B15B21 heterozygotes were superior in all categories to the homozygotes. The results support MHC haplotype differences as the basis for previously observed differences in macrophage functional activation among B‐congenic lines. A gene or genes localized to the B‐complex region apparently controls the intrinsic response of chicken macrophages to inflammatory signals.