The effect of recombinant human interleukin 4 (IL-4) on the expression of antitumor activity of human alveolar macrophages (AM) obtained by bronchoalveolar lavage from healthy donors was examined. AM were incubated for 16 h in medium with various macrophage activators [lipopolysaccharide, des-methyl muramyldipeptide, Nocardia rubra cell wall skeleton, and heptanoyl-γ-d-Glu-(l)-meso-α,ε-A2pm(l)-d-AlaOH] in the presence or absence of IL-4, and then their tumoricidal activity was assayed by measuring 125I-UdR release from human melanoma (A375) cells. The spontaneous tumoricidal activity of AM was slightly suppressed by IL-4 in 3 of 7 donors. Addition of IL-4 to cultures of AM with the activators resulted in dose-dependent suppression of AM-mediated cytotoxicity against A375 cells. IL-4 also inhibited AM-mediated cytotoxicity against A375-R cells, which are resistant to interleukin 1 (IL-1) and tumor necrosis factor α, HT-29 colon cancer cells, and KB cells. IL-4 inhibited the early induction phase of AM activation. Pretreatment of AM with IL-4 also suppressed their expression of antitumor activity in response to lipopolysaccharide. IL-4 inhibited the production of monokines (IL-1 and tumor necrosis factor α) by AM at the protein and mRNA levels. These findings suggest that IL-4 may be important in vivo in the down-regulation of antitumor expression of AM in the lung by inhibiting the production of monokines and other killing mechanisms.

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This work was supported by a grant from the Ministry of Health and Welfare of Japan.

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