A Comprehensive Characterization of Sheep Alveolar Macrophage Function and Responsiveness

Resident alveolar cells were obtained from the in vivo bronchoalveolar lavage of an ovine model. Prior to purification, the cells were primarily comprised of macrophages (82–85%). After Sepracell purification, the cell preparation was 95 ± 1% alveolar macrophages (94% viability). An array of host defense mechanisms were assessed with the following results observed: The phagocytosis of antibody-coated [51Cr]sheep erythrocytes occurred in a time-dependent manner after being measured over 180 min. Phorbol-12-myristate-13-acetate (PMA)-stimulated su-peroxide anion production was 5.5-fold higher than that of resting sheep alveolar macrophages (AMs). Interestingly, when phagocytosis and superoxide anion generation were performed at 39°C (i.e., normal ovine body temperature), they both displayed an enhanced responsiveness compared to 37°C. Chemotaxis was stimulated by PMA in a concentration-related manner. Release of N-acetyl-β-D-glucos-aminidase (NAGA) was maximally stimulated after a 24 h incubation with opson-ized zymosan. Elastase release was undetectable after stimulation with PMA or lipopolysaccharide (LPS). Total cellular elastase levels were measurable only if > 5 × 106cells were used. The secretion of tumor necrosis factor (TNF) was elicited by both PMA and LPS in a concentration-related manner; however, the PMA response was 2.5-fold higher than that of the LPS. This study indicates that the sheep would serve as a responsive animal model for future investigations of the cellular immune system of the lung.