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Bronchoalveolar lavage fluid (BALF) cell profiles, interleukins 1 and 2, (IL-1 and IL-2) and soluble interleukin 2 receptor (IL-2R) levels from patients with pigeon breeders' disease (PBD) (n = 24) and asymptomatic pigeon breeders (n = 10) were compared with those from patients with active sarcoidosis (n = 11), inactive sarcoidosis (n = 10), idiopathic pulmonary fibrosis (n = 25) and normal subjects (n = 10). BALF total cells, lymphocytes and OKT4 receptor-bearing lymphocytes/ml were higher in PBD and active sarcoidosis compared with normals (P less than 0.02 all comparisons). In the asymptomatic pigeon breeders bronchoalveolar (BA) lymphocyte numbers/ml were higher than controls (P less than 0.01) producing a subclinical lymphocytic "alveolitis" in 80% of subjects, although compared with symptomatics, % OKT4 (helper) cell numbers were lower (P less than 0.05). OKT4/OKT8 ratios in both groups were normal, whereas in active sarcoidosis ratios were higher (P less than 0.05) but with considerable overlap. Mean levels of IL-1 and IL-2 were raised in the BALF from all groups compared with normals (P less than 0.01 all comparisons), IL-2 being higher in active sarcoidosis and IPF compared with PBD (P less than 0.01). There was no significant difference in detectable BALF soluble IL-2R between patient groups, although its levels correlated positively with IL-1 (22 paired samples from all groups (rs = 0.8, P less than 0.02) and negatively with % and T-lymphocytes/ml in PBD (rs = 0.75, P less than 0.02, rs less than 0.8, P less than 0.01). However, when BALF soluble IL-2R is expressed in terms of T lymphocytes/ml of epithelial lining fluid (ELF), asymptomatic pigeon breeders had significantly higher levels than their symptomatic counterparts (P less than 0.01). It is concluded that percentage lymphocytes [corrected] are similar in both groups of pigeon breeders, although those with PBD had increased numbers of OKT4 (helper) cells. Patients with active sarcoidosis could not be reliably differentiated from those with acute PBD on the basis of BAL cell profiles. Our results suggest that IL-1 leads to soluble IL-2R formation and that continued antigenic stimulation, as with inhaled pigeon allergens, results in a down regulation of BALF IL-2. Excess BALF soluble IL-2R on a cellular basis suggests a mechanism by which some pigeon breeders remain asymptomatic.