Macrophage subpopulations and macrophage-derived cytokines in sputum of atopic and nonatopic asthmatic subjects and atopic and normal control subjects

Background: Previous studies have shown a prominent macrophage signal in th e bronchial mucosa from nonatopic (intrinsic) compared with atopic (extrins ic) asthmatic subjects. This observation might have represented an expansio n of a proinflammatory macrophage population or a homeostatic mechanism to decrease T(H)2-type inflammation. Objective: The aim of the study was to investigate the numbers of macrophag es and macrophage subpopulations and the expression of IL-10 and IL-12 in s putum from asthmatic and control subjects. Methods: Eight atopic asthmatic (AA) subjects, 10 nonatopic asthmatic (NAA) subjects, 6 atopic control (AC) subjects, and 7 normal control (NC) subjec ts underwent sputum induction. Macrophages were enumerated by using Romanow sky stain and immunocytochemistry (CD68), RFD1 (interdigitating cell marker ) and RFD7 (mature phagocyte marker) mAbs were used for immunocytochemical phenotyping, whereas IL-10 and IL-12 messenger (m)RNA was examined with in situ hybridization by using S-35-labeled riboprobes. The phenotype of cells expressing IL-10 or IL-12 mRNA was examined by simultaneous in situ hybrid ization and immunostaining. Results: No differences in the numbers of CD68(+) macrophages and RFD1(+), RFD7(+), and RFD1(+)/RFD7(+) subpopulations were found between AA, NAA, AC, and NC subjects. However, the numbers of IL-10 and IL-12 mRNA(+) cells wer e increased in AA subjects compared with NAA, AC, and NC subjects (P < .05) , No other differences were found among the groups. Most of the IL-10 and I L-12 mRNA(+) cells in sputum from asthmatic subjects were macrophages (>80% ), with less than 10% of mRNA colocalizing to epithelial cells. Conclusions: Sputum macrophage numbers, unlike tissue macrophages, as previ ously reported, were not elevated in NAA subjects. Increased IL-10 and IL-1 2 expression in atopic asthma may indicate the existence of a homeostatic m echanism to decrease lung inflammation. The lack of such cytokines in intri nsic asthma may predispose to bronchial inflammation in these subjects.