The class-specific immunoglobulin composition of fluids obtained from various levels of the canine respiratory tract

Sensitive and specific radioimmunoassays capable of accurately measuring the three major classes of canine immunoglobulins in the 50 to 200 ng/ml range were developed. The concentrations of IgG, IgA, and IgM in samples of fluid obtained from various levels of the canine respiratory tract (stimulated saliva, tracheal washes, and bronchopulmonary lavage supernatants) and in serum were determined by using the radioimmunoassays. The composition of the immunoglobulin classes, expressed as per cent of the total immunoglobulin content of each sample, differed markedly among the respiratory tract-derived fluids and between respiratory fluids and serum. Pilocarpine-stimulated saliva contained predominantly IgA while bronchial washes contained predominantly IgG. The contents of IgA and IgG in tracheal washes were intermediate between those of stimulated saliva and bronchial washes. There appeared to be a progressive decrease in the content of IgA (83% to 19%) and a progressive increase in the content of the IgG (6.3% to 75%) as sampling proceeded from the upper to the lower respiratory tract. The mean IgG/IgA ratios were as follows: stimulated saliva, 0.1; tracheal washes, 2.1; bronchial washes, 4.1; and serum, 23.2. All respiratory tract-derived fluids contained small amounts of IgM. Local and systemic immunization with sheep erythrocytes failed to alter the per cent composition of immunoglobulins in bronchial washes during the primary immune response. The results demonstrate major differences in the composition of immunoglobulins derived from the upper as opposed to the lower respiratory tract. The findings suggest that functional differences may exist in the immunologic apparatus associated with various levels of the respiratory tract.