Heterogeneity in Immunologic Functions among Canine Alveolar Macrophage Subfractions

Abstract

Canine alveolar macrophages (AM) were examined for the presence of subpopulations with differnt immunologic functions. Lavaged bronchoalveolar cells (BAC) from normal beagle dogs were separated into 3 density subfractions by centrifugation through discontinuous gradients of Percoll solution. After incubated on plastic plates, each of adherent BAC subfractions recovered was identified as AM by morphologic criteria and phagocytic capacity of latex beads. These adherent BAC subfractions were then incubated with lipopolysaccharides (LPS) and/or silica for testing their capacity to produce interleukin 1 (IL-1). Il-1 activity of culture supernatants was greater both in the lowest and intermediate density subfractions, but much lower in the highest density subfraction. When each of adherent BAC subfractions was incubated with autologous nylon wool-passed lymphocytes from tracheobronchial lymph nodes in the presence of a lectin mitogen, phytohemagglutinin (PHA), proliferative responses of lymphocytes were prominently enhanced by increasing cell numbers of adherent BAC subfractions. On the contrary, another mitogen, concanavalin A (Con A)-induced lymphocyte responses were suppressed by addition of both of the lowest and intermediate density subfractions, whereas only the highest density subfraction enhanced lymphocyte response. The suppressive effect of adherent BAC subfractions on Con A-induced responses was, however, inhibited by addition of indomethacin, prostaglandin synthesis inhibitor. These results indicate the presence of functional subpopulations among canine AM with respect to IL-1 production and accessory cell, function for mitogen-induced lymphoproliferation.