Increased levels of soluble serum interleukin-2 receptor in extrinsic allergic alveolitis correlate with interleukin-2 receptor expression on alveolar macrophages.

In a group of 20 patients with extrinsic allergic alveolitis (10 with farmer's lung, 9 with bird-breeder's lung, and 1 with humidifier's lung), we observed increased levels of soluble serum interleukin-2 receptor (ssIL-2R) with an average of 75.2 pmol (control group average, 40.6 pmol). Analysis of bronchoalveolar lavage cells by immunocytochemistry with a CD25 antibody revealed only a slight increase to 4.2% IL-2R+ cells among alveolar lymphocytes but a pronounced rise to 21.2% IL-2R+ cells among alveolar macrophages. Furthermore, cytometry revealed a fourfold higher IL-2R expression on a per cell basis for alveolar macrophages as compared with alveolar lymphocytes. A clear-cut positive correlation (p = 0.006) was found for ssIL-2R and IL-2R+ alveolar macrophages, but only a borderline correlation was found for ssIL-2R and IL-2R+ alveolar lymphocytes (p = 0.04). The finding of a concomitant decrease of IL-2R+ alveolar macrophages and of ssIL-2R on allergen avoidance further supports the notion that alveolar macrophages may be the main source of the increased ssIL-2R in patients with extrinsic allergic alveolitis.