The Effect of Intravenous Antigen on Circulating Monocytes in Animals with Delayed Hypersensitivity

Abstract

A study was made of the effect of intravenous antigenic challenge on the levels of circulating leukocytes in delayed sensitive rats and guinea pigs. A sharp decrease in the level of blood monocytes was observed 6 hr after antigenic challenge. This drop was generally followed after 24 hr by a compensatory increase in the number of these cells in the circulation. The decrease and subsequent rebound of the level of blood monocytes following antigenic challenge was shown to be a systemic manifestation of delayed hypersensitivity and could not be elicited by the passive administration of antibody followed by antigen. The increase in blood monocytes observed 24 hr after challenge was found to be the result of the release of new cells from the bone marrow. No effect of antigenic challenge was detected on the levels of circulating lymphocytes or polymorphonuclear cells. The relationship between these phenomena and in vivo and in vitro manifestations of delayed hypersensitivity is discussed.