Lung Lymphocytes: Origin, Biological Functions, and Laboratory Techniques for Their Study in immune-Mediated Pulmonary Disorders

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Abstract
Different types of immunocompetent cells, including T lymphocytes and alveolar macrophages, account for pulmonary host defense. Taking advantage of the availability of the monoclonal antibody technique, cell culture facilities, pure recombinant cytokines, and molecular probes for their genes, in the last few years it has been possible to keenly study the different steps that lead to the compartmentalization of immune response in human lung. Furthermore, the immunological analysis of cells retrieved from bronchoalveolar lavage (BAL) allowed recognition of the importance of immune mechanisms in the evolution of immune-mediated pulmonary disorders. The purpose of this review is to summarize recent advances on the immunologic characterization of lung lymphocytes in health and disease. Following a brief description of the pathways through which the pulmonary lymphoid system contributes to removing potentially harmful inhaled antigenic materials, available laboratory techniques to evaluate the lymphoid component of the pulmonary immune system and their byproducts are discussed. These techniques cover methods for preparing lymphocytes from the BAL fluid and for characterizing lung lymphocytes both in cell suspensions and pulmonary tissue biopsies. Other sections of this review describe the techniques for measuring the immunologic effector functions of lung lymphocytes. We also provide the reader with a flavor of the molecular biology methods used to characterize lymphocytes in the pulmonary microenvironment. The final sections of the review article highlight the pathogenetic role envisaged for lymphoid cells in pulmonary disease states and emphasize the importance of the BAL analysis in the clinical management of the most relevant immune-mediated lung diseases.