Cell surface changes of in situ macrophages induced by superimposed antigen

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Abstract
Mice received an injection of sheep erythrocytes (SRBC) into the footpad “prepared” or “not prepared” with a 7‐day‐prior injection of a protein‐bound polysaccharide from Coriolus versicolor (PSK; KrestinR), and the ultrastructure of in situ macrophages was studied at various intervals after the injection. A single SRBC injection into the footpad induced linear cell arrangements of several macrophages. The macrophages showed no prominent morphological alterations after SRBC digestion. When PSK‐stimulated subcutaneous macrophages were challenged by SRBC, they rapidly sent out numerous long cytoplasmic projections which radiated in all directions. Such projections of neighboring macrophages tended to contact one another. At the following stage, a pronounced sequential alteration was noted, characterized by the interlocking of elongated projections. This provided massive aggregations of “activated” macrophages. These observations suggest the possibility that intercellular communication among “activated” macrophages was elicited, particularly in the subcutaneous region, and maintained through an intensive interaction of cytoplasmic projections. Further, the present results histologically support our previous report which shows that the “PSK‐prepared” footpad site but not the “prepared” one supports development of a splenic humoral immune response following injection of superimposed SRBC.