Porcine Alveolar and Pulmonary Intravascular Macrophages: Comparison of Immune Functions

Abstract

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.

Depletion of pulmonary intravascular macrophages partially inhibits lipopolysaccharide-induced lung inflammation in horses

“…However, it is possible that a larger sample size may have resulted in a significant response in diastolic and systolic pressures. Although the vasoactive mediators secreted by the equine PIMs remain unknown, it is possible that as with porcine PIMs, these cells may produce arachidonic acid metabolites following the uptake of the LPS [7,8]. Therefore, PIM depletion will eliminate a vascular source of pro-inflammatory vasoactive substances to reduce LPSinduced pulmonary arterial hypertension.…”

“…This hypertensive response, however, is abolished following removal of PIMs [27]. In vitro evidence shows that porcine PIMs can metabolise arachidonic acid [7,8]. We have recently shown that bovine PIMs contain TNF-α and their depletion significantly inhibits the accumulation of inflammatory cells and pathology in acute lung disease in calves [26].…”

Immunophenotypic characterization and depletion of pulmonary intravascular macrophages of horses

“…In the lungs, macrophages occur in the airways, alveolar spaces, interstitium, and microvessels. Pulmonary intravascular macrophages (PIMs) were recently identified as resident mononuclear phagocytes in cattle, sheep, goats, pigs and horses [4,5,7,29,35]. PIMs differentiate from monocytes in post-natal life and form firm adhesions with the capillary endothelium [15,[36][37][38].…”

“…Neonatal lambs that do not have PIMs show diminished pulmonary vascular response to tracers compared with four-week old lambs that have PIMs [15]. Blecha et al showed that porcine PIMs secrete thromboxane and are cytolytic [7,8]. They also reported that the immunological characteristics of PIMs are similar to those of alveolar macrophages [8].…”

Intrinsic Microbicidal Activity and Pulmonary Hypertension in Isolated Newborn Piglet Lungs

“…Miyamoto et al (15) reported a similarly restricted localization of inert microspheres in sheep lungs. PIM in vitro are phagocytic, although less so than alveolar macrophages (16), and generate substantial amounts of eicosanoids, including those incriminated in GBS-induced pulmonary hypertension, as well as various cytokines (16,17). Collectively, these findings support the view that PIM play a major role in clearance of CBS as it transits the pulmonary vascular bed and that clearance of the bacteria is important for release of mediators that incite the hypertensive response and attract additional inflammatory cells (e.g.…”