Immunoglobulin Secreting Cells

(P < 0.02). The mean number of IgA secreting cells in bronchial lavage fluids was 633 per million lymphocytes as compared to 100 per million lymphocytes in peripheral blood (P < 0.005). Thus, compared to peripheral blood, cells from the lavage fluids were relatively enriched for both IgG and IgA secreting cells. However, IgA secreting cells were the major class of immunoglobulin secreting cells in bronchial lavage fluids, whereas IgG secreting cells predominated in peripheral blood. The prominence of IgA secreting cells in bronchial lavage fluids was further demonstrated by a mean ratio of IgA/IgG secreting cells in bronchial lavage fluids of 1.26 compared to a ratio in peripheral blood of 0.57 (P < 0.02). Cells secreting IgM were identified in only four of seven bronchial lavage fluid samples studied but in all peripheral blood samples. IgE secreting cells were not present in normal peripheral blood but could be demonstrated in 5 of 11 lavage fluid specimens. Thus, cells actively secreting immunoglobulins can be identified in the lower bronchial-alveolar tree ofnormal human subjects. Cells secreting IgG, IgA, or IgM may function in local lung defenses against infection; cells secreting IgE may contribute to hypersensitivity reactions in the lung. Dr. Martin receives support from a Research Career Development Award from the National Institutes of Health (Al70335). Address reprint requests to Dr. Lawrence, Pulmonary Section, Department of Medicine, The Methodist Hospital, Texas Medical Center, Houston, Tex. 77030. Received for publication 1 June 1978. INTRODUCTION The lung is an immunocompetent organ capable of an antibody response to particulate antigen (1-3). Cells with immunologic capabilities can be demonstrated in the lung parenchyma (3, 4), the bronchial associated lymphoid tissue (5), and the distal bronchial-alveolar airways (6, 7) in animal models as well as in man. The relative composition of cells from the human lower bronchial-alveolar tree, obtained by fiberoptic bronchoscopy and bronchial lavage, has been well defined (8-10), and the functional capabilities of these cells are now being investigated by several laboratories (11, 12). In the present study, we have assessed the immunoglobulin secretory capacity of normal human bronchialalveolar cells, by a modified reverse hemolytic plaque assay (13). In this assay, indicator sheep erythrocytes (SRC)l that have been precoated with Protein A (Staphylococcus aureus) are mixed in agar with mononuclear cells in the presence of rabbit IgG developing antisera specific for either human IgG, IgA, IgM, or IgE. Because Protein A has an affinity for the Fc portion of IgG, the developing antisera, bound to the secreted immunoglobulin of the appropriate class, bind to the Protein A-coated SRC as an immune complex. With the addition of complement, the immune complex-laden SRC surrounding an immunoglobulin secreting cell are lysed, producing a plaque. Such plaques have been shown to be inhibitable by cycloheximide (14, 15), a reversible inhibitor of protein synthesis, but not by maneuvers to remove cytophilic immunoglobulins (16). Thus, with monospecific developing antisera, it is possible to identify cells actively secreting either IgG, IgA, IgM, or IgE in bronchial lavage fluids or peripheral