Peroxidase arthritis. 3. Sequential changes in cellular composition of the developing inflammatory infiltrate

Repeated daily injections of horseradish peroxidase into rabbit knee joints lead to a characteristic sequence of cellular events. Early transient infiltration with polymorphonuclear leukocytes was followed by a progressive increase in the number of macrophages. This appeared to represent, at least in part, a consequence of increased emigration of monocytes. Subsequently, increasing numbers of lymphocytes appeared. Many of the lymphocytes had frequent cytoplasmic polyribosomes. By the eighth or ninth day, immunoblasts, plasmablasts and immature plasma cells were observed; cytochemical evidence of local specific antibody synthesis first was demonstrated in such cells at this stage. These results demonstrate the sequential cellular events in an immunologic inflammatory response to local antigen. Questions remain concerning the stimulus for early monocyte emigration and macrophage accumulation, and the site of initial sensitization of lymphocytes; these problems are discussed.