Human monocyte aggregation in vitro.

Human peripheral blood monocytes can be used in an aggregation test for delayed hypersensitivity. Aggregation occurs when monocytes are incubated with supernatants from cultures of sensitized lymphocytes stimulated with antigen in vitro. Although monocyte aggregation was observed macroscopically and by light microscopy, electron microscopic examination revealed no differences between aggregated cell suspensions and non-aggregated control monocytes; microvilli were prominent in both preparations.