A physiologic differentiation between delayed and immediate hypersensitivity.

Studies have been made of movement of various macromolecules into and out of the pleural space of guinea pigs during the course of a delayed hypersensitivity reaction to purified protein derivative (PPD), and a passively transferred immediate hypersensitivity reaction to ovalbumin. While the immediate hypersensitivity reaction transiently alters vascular permeability as shown by increased movement of macromolecules into the chest, the delayed hypersensitivity reaction is marked by a decreased capacity to resorb macromolecules from the pleural space. The data suggest that the two hypersensitivity reactions may be distinguished by these physiologic differences. Additional data from studies of a chemically induced pleural effusion in these animals suggest that some type of outflow obstruction is necessary for the development of effusion, but that the outflow defect caused by the irritating chemical is based on a different mechanism than that seen during the delayed hypersensitivity reaction.