The pulmonary inflammatory response. Cellular events in experimental pulmonary arterial hypersensitivity disease

Horseradish peroxidase (HRP) or bovine serum albumin (BSA) were covalently linked to polyacrylamide or agarose beads and were injected into control Syrian hamsters and hamsters previously immunized with either HRP or BSA. Animals sensitized to soluble antigen and subsequently challenged intravenously with the same antigen immobilized on beads developed an acute focal inflammatory response within 2 to 6 hours after injection. The acute response involved local deposition of IgG and complement (beta1A/beta1C globulin), polymorphonuclear leukocyte exudation, and variable amounts of hemorrhage. A focal vasculitis was occasionally present. Within 72 hours the reaction had become largely mononuclear or granulomatous in nature, and giant cell formation was seen within 4 days after immobilized antigen injection. Severe reactions developed only upon recognition of specific antigenic determinants; thus hamsters immunized against soluble HRP developed characteristic lesions only upon intravenous challenge with HRP-coated beads but not with beads coated with unrelated antigen (BSA). The beads elicited only a mild foreign body reaction in the control hamsters at 5 to 7 days after injection which was temporally and histopathologically distinct from the lesions in immunized hamsters. Thus, the state of existing immunity can influence the character and severity of the local pulmonary inflammatory response.