Human alveolar macrophages: antigen-independent binding of lymphocytes

To characterize the initial step in alveolar macrophage (AM)-lymphocyte (L) interaction in the human lung, we studied the ability of human AM to bind autologous blood L in vitro in the absence of antigen. AM were obtained by saline bronchial lavage through a fiberoptic bronchoscope. Monolayers of AM attached to glass bound autologous blood L prepared by Ficoll-Hypaque and nylon wool column separation. The AM-L binding increased from zero time to a maximum at 2 h and then declined to a zero time value at 18 h. The binding was dependent on the number of L added to the AM monolayers, with greatest binding at an AM:L ratio of 1:50. AM:L binding required viability of AM, but not of L, and was temperature dependent. Pretreatment of AM with iodoacetic acid, trypsin, neuraminidase, or colchicine diminished attachment of L at 2 h. Neuraminidase pretreatment of L resulted in increased binding to nontreated AM. Thus, a physical interaction between human AM and autologous peripheral blood L can occur in vitro in the absence of known antigen; similar interaction in vivo may play a role in the generation of cell-mediated immune responses in the lung.