Macrophage‐Lymphocyte Clusters in the Immune Response to Soluble Protein Antigen in Vitro

T cells from immune guinea-pigs produce clusters in vitro with macrophages pulsed with soluble protein antigens. The formation of clusters is antigen-specific. Time-lapse cinephotomicrography was used to study the sequence of events leading to cluster formation and the kinetics of already formed clusters. The central lymphocyte attaches through a broad base to the macrophage during the first few hours of incubation. After several hours, during which the central lymphocyte is situated alone on the surface of the macrophage, free lymphocytes begin to interact for shorter or longer periods of time through their uropods with the central lymphocyte, thus acting as peripheral lymphocytes. In spite of a frequent traffic of peripheral lymphocytes in and out, the cluster is a relatively stable structure. Occasionally the entire complex of lymphocytes leaves the macrophage, moves randomly in the culutre and attaches to a new macrophage or returns to the same macrophage.