ACCESSORY CELL-FUNCTION OF RABBIT ALVEOLAR MACROPHAGES

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Abstract
Alveolar macrophages (AM) are the 1st cells to contact inhaled antigen. Accessory cell function of AM would modulate the immunologic response to antigenic exposure. The capability of AM to act as accessory cells for proliferation of lymphocytes was examined using conditions that are best suited for expression of this function. Rabbit popliteal lymph node cells, both before and after depletion of macrophages by 2 successive Sephadex G-10 columns that decreased nonspecific esterase positive cells from 2.56 to < 0.1% and abolished or markedly decreased concanavalin A-induced lymphocyte proliferation were used. AM were lavaged from rabbit lungs and treated with mitomycin C. AM enhanced proliferation of 5 .times. 104 and 7 .apprx. 104 unseparated, lymph node cells 5- to 15-fold, but had no effect on 2 .times. 105 cells. The optimal ratio of macrophages to lymphocytes (AM:L) was between 1:2 and 2:1. An AM:L value of 4:1 suppressed proliferation. The addition of AM to macrophage-depleted lymph node cells enhanced proliferation of 5 .times. 104, 7 .times. 104 and 2 .times. 105 lymphocytes 15- to 50-fold (AM:L, 1:2 to 2:1). Excessive numbers of macrophages (AM:L, 4:1) suppressed proliferation 5- to 50-fold. Rabbit AM can act as accessory cells in assays of mitogen-induced lymphocyte proliferation with maximal effect of AM:L values of 1:2 to 2:1. Suppression can occur as a result of excessive numbers of macrophages.