Immunoglobulin G Subclass Proteins in Serum and Lavage Fluid of Normal Subjects

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Abstract
Although total concentration of immunoglobulin G was quantitated in the lower respiratory tract of humans, the contribution of the 4 subclass species of IgG tototal recoverable IgG protein was not assessed. Sensitive, micro-ELISA [enzyme-linked immunosorbent assay] assays specific for the individual subclasses were developed and employed to measure serum and local intrapulmonary levels of these proteins. Lung lavage was compared with and serum concentrations of these proteins (relative to albumin) and also these immunoglobulins were compared with IgA and IgE. The results of serum level measurements of subclass proteins were similar to results reported by others; IgG, and IgG were present in lung lavage in concentrations similar to their serum concentration, serum and lavage levels were directly related and IgG increased in lavage compared with that in serum, suggesting increased local synthesis or accumulation of this protein within the lower respiratory tract. Local intrapulmonary concentrations of both IgA and IgE also increased compared with those in their serum concentrations. Local IgG was variable, some subjects had increased amounts compared with that in serum, whereas others had concentrations similar to those in serum. A preferential accumulation of IgG4 was suggested in the lower respiratory tract. IgG4, like IgA and IgE, may play a special role in the immune defense of the lung.