[Immunological studies in hypersensitivity pneumopathies].

In immunological investigations in hypersensitivity pneumonia some have a diagnostic value for the clinician but many others are essentially of interest in research and in analysing the pathophysiology. Unfortunately, skin tests with the responsible antigens are often positive in patients but also in exposed subjects without the lung disease. Studies on peripheral blood require a search for IgE immediate hypersensitivity which is rarely positive and above all a search for precipitating antibodies by the different standard tests available: there again, positive findings occur often enough in exposed but asymptomatic subjects; the sensibility and specificity of cell-mediated hypersensitivity tests seem much more reliable. The study of cell populations in broncho-alveolar lavage fluid generally shows an inverted T4:T8 lymphocyte ratio; a functional analysis seems to show a high degree of lymphocyte activation, which may be of T4 or T8 phenotype whilst cytotoxic lymphocyte activity would be exclusively found in the patients and not in asymptomatic exposed subjects. The provocation test, as long as it is positive, is one of the firmest elements in a diagnosis, above all if one takes care to couple this with a study of the lavage. Finally, the satisfaction of the immuno-histological criteria is currently rarely required to confirm the presence of hypersensitivity pneumonitis.