Modulation by lymphocytes of the vascular effects caused by inflammatory mediators and carrageenin in the rat.

Inhibited permeability responses to intradermally injected histamine, serotonin and bradykinin were observed in leucopenic rats, when compared to those measured in normal animals. Significant reversal of the inhibited responses was seen when leucopenic rats were given suspensions of lymphocytes i.v. Suspensions of PMN granulocytes, however, were ineffective. In both cases, the volumes of the suspensions contained adequate quantities of the particular cells to counteract their deficiency. Histological changes provoked by carrageenin in the paws of leucopenic rats injected with suspensions of lymphocytes resembled those of normal rats, the main difference being that the number of cells which had emigrated into the affected tissues was reduced. In leucopenic controls or leucopenic animals injected with suspensions of PMN granulocytes, minimal histological alterations were observed. It is concluded that lymphocytes play a role in the development of acute inflammatory reactions.