Effects of alveolar surfactant aggregates on T-lymphocyte proliferation

The effects of alveolar large aggregate (LA) and small aggregate (SA) surfa ctant subfractions isolated from healthy adult rats on mitogen-stimulated p roliferative responses of human peripheral blood mononuclear cells (PBMC) w as examined. Various concentrations of total surfactant suppressed prolifer ation of stimulated lymphocytes by up to 95% of mitogen-stimulated cells al one. LA subfractions of total surfactant had no effect on proliferation. wh ereas SA significantly enhanced the lymphocyte proliferation at lower conce ntrations (7.8 mug/ml) compared to mitogen-stimulated cells alone. Higher c oncentrations of SA (62.5 mug/ml) inhibited lymphocyte proliferation. This concentration-dependent effect of SA on proliferation of PBMC was also pres ent when cells were stimulated with various lectins including anti-CD3, con canavalin A and phytohemagglutinin. Analysis of the supernatant of mitogen- stimulated cell cultures treated with inhibitory concentrations of SA showe d decreased amounts of interleukin (IL)-2, compared to cells alone. which c ould be reversed by adding exogenous IL-2 to the cell cultures with the SA. These results suggest that alveolar surfactant subfractions have distinct functions within the alveoli, both biophysically and with respect to their effects on the host's immunomodulatory responses. (C) 2001 Elsevier Science B.V. All rights reserved.