Concentrations of immunoglobulin classes in subcompartments of the sheep lung

The concentrations of IgA, IgG and IgM were measured in plasma, lung lymph and lung lavage fluid from adult sheep. Immunoglobulin concentrations in lymph and lavage fluid should fall sequentially during diffusive flux from the vascular compartment as a result of molecular sieving at the capillary endothelium and the alveolar epithelium. This was seen only for the IgG class. High concentrations of IgA and IgM in the interstitial (lymph) and luminal (lavage) compartments of the lung (relative to plasma levels) suggest either local synthesis of these classes or the existence of class specific active transport.