Background: The precise mechanisms involved in the pathogenesis of hypersensitivity pneumonitis (HP) have not been identified. HP is characterized by inflammatory lymphocytic alveolitis and a remarkable increase in T-lymphocytes detected in bronchoalveolar lavage fluid (BALF). It is suggested that both CD4+ and CD8+ T cells may contribute to the pathogenesis of HP. Experiments on animal models suggest that cell mediated immunity (CMI) is more important for the pathogenesis of HP than complex-mediated immunity, but the relationship between the subsets of BALF lymphocytes and humoral or cell-mediated allergic reactions is still not clear. The aim of our study was distinguish CD4+ and CD8+ T cells in BALF lymphocytes during a delayed--type hypersensitivity (DTH) reaction in the lung.
Material and methods: The experiment was performed on guinea pigs sensitized with BCG vaccine and subjected to a single inhalation of tubercle bacilli antigens (tuberculin). 24 hours after tuberculin provocation (at the time of maximum lymphocyte infiltration), bronchoalveolar lavage was performed on both sensitized and non--sensitized (control) animals. The total cell count was estimated, and a differential microscopical examination of BAL-fluid cells was performed, along with the phenotyping of BALF lymphocytes (by flow cytometry).
Results: In the BALF of the sensitized animals, as compared to the controls, there was a statistically significant increase in the percentage and absolute count of T-lymphocytes, CD4+ and CD8+. The CD4 / CD8 ratio in both groups did not differ significantly and was individually variable (2.94±0.72 SEM in the experimental group, vs 4.41±1.29 SEM in the control group).
Conclusion: Both CD4+ and CD8+ lymphocytes (with some predominance of helper cells) participate in the efferent phase of the delayed type hypersensitivity reaction in the lung induced by antigen inhalation.

Keywords: hypersensitivity pneumonitis, delayed-type hypersensitivity, BALF, CD4+/CD8+, Guinea Pigs