Heterogeneity in immunologic functions of rat alveolar macrophages--their accessory cell function and IL-1 production

Alveolar macrophages (AM) from normal rats were separated into 4 different density fractions by centrifugation on a discontinuous Percoll gradient. These fractionated (I-IV) AM, as well as unfractionated (UF) AM, were then tested for their capacities to regulate mitogen-induced T cell proliferation. Concanavalin A (Con A)-induced response of nylon wool-passed non-adherent splenic T lymphocytes was suppressed by addition of UF or higher density (III and IV) AM, while an intermediate density (II) AM fraction could enhance T cell response in a dose-dependent manner. Similar effects of UF or fractionated (I-IV) AM on T cell responses were noted when the cultures were exposed in vitro to inert, non-fibrogenic titanium dioxide (TiO2) particles. On the contrary, T cell response was sustained by addition of UF or higher density (III and IV) AM, and was also more prominently enhanced by an intermediate density (II) AM after the in vitro exposures to fibrogenic dust particles, like silica and asbestos. Higher interleukin 1 (IL-1) activity was detected from these silica- or asbestos-exposed cultures of UF and fractionated (II, III, and IV) AM. The IL-1 activity was also highly detectable from the cultures of an intermediate density (II) AM fraction when cultures were unexposed or exposed in vitro to TiO2 particles. The Ia antigen expression on the surface of UF or fractionated (II, III, and IV) AM was elevated in the Con A-pulsed co-cultures, but not significantly different whether or not they were exposed in vitro to dust particles. These results may indicate the presence of heterogeneity in accessory cell functions and IL-1 production among rat AM.