Is the different T helper cell activity in sarcoidosis and extrinsic allergic alveolitis also reflected by the cellular bronchoalveolar lavage fluid profile?

Background - Sarcoidosis is generally characterized by a CD4⁺ lymphocyte predominance in bronchoalveolar lavage fluid (BALF), whereas in extrinsic allergic alveolitis (EAA) a CD8⁺ lymphocyte predominance is found. However, we have previously demonstrated an increase in CD4⁺ lymphocytes in BALF obtained from EAA patients as well. The aim of this study was to evaluate whether in sarcoidosis and EAA the BALF cellular profile - even without the help of cytokine detection - might reflect differences in the CD4⁺ T-lymphocyte subpopulations, i.e. T helper (TH)-1 and TH2 lymphocytes. Methods - For this purpose, we analyzed BALF analysis results obtained from 77 nonsmoking patients with histologically proven sarcoidosis and 54 nonsmoking patients suffering from EAA. Results - Patients with EAA showed the highest mean absolute numbers of lymphocytes, CD8⁺ as well as CD4⁺ T lymphocytes, whereas the percentage of CD4⁺ T lymphocytes in BALF was low. In contrast, patients with sarcoidosis showed the lowest absolute and relative number of CD8⁺ T lymphocytes, the highest percentage of CD4⁺ T lymphocytes and CD4⁺/CD8⁺ ratio. Moreover, patients with Lofgren's syndrome demonstrated an alveolitis suggesting a TH1 lymphocyte-subset-like predominant related profile, characterized by lower numbers of eosinophils and mast cells, whereas sarcoidosis patients with respiratory symptoms formed a more mixed TH1/TH2 pattern. Patients with EAA showed a cellular BALF profile suggesting a functional predominance of TH2 lymphocytes. Conclusion - These preliminary data suggest a different distribution of the CD4⁺ T lymphocyte subtypes characterized by a functional heterogeneity of CD4⁺ T lymphocytes between - as well as within - these various pulmonary disorders. The exact role of this imbalance of TH1 and TH2-like activity in the lung with regard to the pathogenesis and prognosis needs to be further elucidated.