Cellular Activities in Hypersensitive Reactions

Abstract

Summary As has been shown in other studies, mononuclear infiltration is the chief cytologic feature which eventually distinguishes the tuberculin from the Arthus reaction. Although the earliest infiltrating cells in both cases are polymorphonuclears, these are followed, in the site of the tuberculin reaction, by large mononuclear cells (medium lymphocytes and monocytes) and small lymphocytes. The small lymphocyte seems to be implicated in the damaging aspects of the delayed reaction; this is especially evident in the epidermis which these cells invade. This may also be the cell involved in the initial damage to the vascular endothelium which triggers the reaction. The small lymphocyte may succumb to the reaction. The contribution of other mononuclear cells, which appear to transform almost completely into macrophages by about 48 hr after the injection of test antigen, is not known. The “Jones-Mote” reaction unfolds cytologically as does the delayed one in general outline, but at a slower rate and with certain quantitative and qualitative differences. There is no invasion of epidermis or tissue death, and the number of small lymphocytes is low relative to that seen in the delayed reaction. A greater proportion of the mononuclear cells in this reaction eventually give rise to plasma cells. In view of the fact that in this hypersensitive state the reactivity just precedes the appearance of detectable humoral antibodies and often wanes rapidly thereafter, it is conceivable that small quantities of antibody produced by cells just entering into synthesis might bring about damage to the vascular endothelium with some subsequent cellular infiltration but without that component, i.e., cell damage, which in the delayed reaction is mediated by further interaction between antigen and the incoming sensitive small lymphocytes.