Lung humoral response to Pseudomonas species.

Immunoglobulin G (IgG) is quantitatively the predominent immunoglobulin protein in the distal airway of the human host. IgG enters the distal lung from circulating pools and plasma cells located largely in the interstitium. Although all four IgG subclasses are present in human lung secretions, only subclasses G3 and, to a lesser degree, G1 attach to pulmonary macrophage membrane receptors. IgG opsonic antibodies are essential for the optimal clearance of a very troubling pathogen. Pseudomonas aeruginosa. Nosocomial pneumonia caused by this gram-negative bacillus responds poorly to potent antimicrobial agents and is associated with a 70% mortality. To a great extent the morbidity and mortality resulting from nosocomial pneumonia caused by Pseudomonas spp. are attributable to ineffective humoral immune response to this bacterium. IgG2 antibodies in response to pseudomonal lipopolysaccharide are poorly opsonic in the macrophage system, and derepression of the potent pseudomonal elastase, an enzyme with broad substrate specificity, contributes to the disruption of other IgG antibodies.