Porcine alveolar and pulmonary intravascular macrophages: comparison of immune functions.

Although a substantial amount of information is available on pulmonary alveolar macrophages (PAMs), little is known about pulmonary intravascular macrophages (PIMs), a separate population of lung macrophages found apposed to the endothelium of pulmonary capillaries. We compared these two populations of lung immunocytes to determine their relative immunological activity. Our results suggest that PAMs are more phagocytic than PIMs; however, PIMs may be more efficient at lysing ingested bacteria than PAMs. Although similar in antibody-dependent cellular cytotoxicity, PIMs are more spontaneously cytolytic than PAMs. Depending upon the effector:target cell ratio studied, the tumoricidal activity of PIMs was less than or equal to that of PAMs. Both cell populations produced the cytokines interleukin-1 and tumor necrosis factor-alpha at similar concentrations. These data suggest that PIMs are immunologically active, although the degree of activity may differ between PIMs and PAMs.