Cytokine production by rabbit alveolar macrophages: Differences between activated and suppressor cell phenotypes

The differences between cytokine-producing profiles of activated macrophages (A-Mφ) and suppressor macrophages (S-Mφ) were examined. A-Mφ, which exhibited cytotoxicity against RK-13 cells, were generated from resident rabbit alveolar Mφ by treatment with lymphokine solution (culture fluids of rabbit spleen cells stimulated with concanavalin A [Con A]). S-Mφ, which were able to inhibit cellular proliferations of rabbit spleen cells stimulated with Con A, were generated from resident alveolar Mφ by treatment with 1-methyladenosine (an immunosuppressive molecule in tumourous ascites fluids). When A-Mφ were stimulated with lipopolysaccharide (LPS) in vitro, the cells produced significantly more interleukin (IL)-1 (~1.4 times), IL-6 (~2.1 times), IL-12 (~60 times), and tumour necrosis factor-α (TNF-α) (~37 times) than did resting macrophages (R-Mφ) stimulated with LPS as control cells. After the stimulation with LPS, both A-Mφ and R-Mφ did not produce transforming growth factor-β (TGF-β). In contrast, when S-Mφ were stimulated with LPS in vitro, the cells produced significantly more TGF-β (~1.6 times) and significantly less IL-6 (~1.8 times) than did control cells. Also, S-Mφ did not produce IL-1, IL-12, and TNF-α into their culture fluids after the stimulation with LPS. These results show the differences between cytokine-producing profiles of A-Mφ and S-Mφ and characteristics of their cytokine-producing profiles are analogous to T cell subsets. Differences displayed in the cytokine profiles may contribute to the effector (A-Mφ) or the suppressor (S-Mφ) functions of alveolar Mφ.