Interleukin-4 production by human alveolar macrophages

IL-4 is a key factor for T helper type 2 (Th2) differentiation and Ig class switching to IgE and IgG(4) during the development of immune responses. IL-4 is produced by T cells, mast cells, basophils, and eosinophils. However, there is also evidence suggesting that rat alveolar macrophages (AMs) produce IL-4.

Given the importance of AMs and Th2-related diseases in the lung, we investigated the production of IL-4 by human AMs.

Human AMs were isolated from bronchoalveolar lavage, purified, and IL-4 production was investigated at mRNA and protein levels using real-time PCR, flow cytometry, immunocytochemistry, and ELISA. The presence of IL-4 was investigated in subjects with asthma or asymptomatic airway hyper-responsiveness, and in normal non-smokers.

IL-4 and IL-4delta2 (a splice variant found in other IL-4 producing cells) mRNAs were found in all these subjects, but IL-4 expression could not be correlated with a particular disease. Protein production was verified by immunocytochemistry and flow cytometry analysis demonstrating, respectively, up to 69% and 59% positive AMs, regardless of the subject condition. Furthermore, phorbol-12-myristate-13-acetate and calcium ionophore stimulated the release of IL-4 after 48 h treatment in the presence of anti-IL-4 receptor antibody.

Our results show for the first time that IL-4 and IL-4delta2 mRNA are expressed and IL-4 protein produced and released by human AMs, suggesting a contribution of these cells in the modulation of Th2 immune response.