Macrophage antimicrobial functions in a chicken MHC chromosome dosage model

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Abstract
Macrophages respond to certain inflammatory signals with a marked increase in respiratory burst and the production of reactive oxygen intermediates; these metabolites play an essential role in the destruction of invading microorganisms. In this study, macrophage antibacterial inflammatory responses were compared among chickens having two (disomic), three (trisomic), or four (tetrasomic) copies of the major histocompatibility complex (MHC)–encoding microchromosome (B 15 haplotype). Phorbol myristate acetate (PMA)–stimulated superoxide anion (O2 -) production by cross-linked dextran (Sephadex)–elicited peritoneal macrophages was measured at early (4 h), intermediate (24 h), and late (42 h) stages of the inflammatory response using ferrocytochrome c reduction. Significantly elevated O2 - production was observed for trisomic versus disomic macrophages during both early and intermediate stages of the inflammatory response. Late in the response, tetrasomic macrophages produced a significantly higher level of O2 - than disomic cells. When PMA was used to trigger hydrogen peroxide (H2O2) production, no significant genotype difference was found for any stage of the inflammatory response. Phagocytosis of heat-killed Salmonella enteritidis by macrophages differed among the three genotypes: trisomic macrophages were superior to disomic cells during early inflammation, no genotypic difference was observed at the intermediate stage, and disomic cells had greater phagocytic capacity than aneuploid macrophages late in the response. Likewise, when S. enteritidis was cultured with macrophages to induce oxygen intermediate secretion, H2O2 production followed a kinetic pattern among the genotypes similar to that observed for bacterial phagocytosis. Endogenous superoxide dismutase (SOD), catalase, and glutathione peroxidase (GP) activities were determined for the macrophages during intermediate and late inflammatory stages. Tetrasomic macrophages had reduced SOD activity at the late stage, no significant difference was observed in catalase activity among genotypes at either time point, and trisomic macrophages had enhanced GP activity compared to disomic cells at both time points. These results indicate that differences in MHC gene dosage are associated with differences in chicken macrophage activation for the acquisition of selected antibacterial functions.

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