Abstract
Plasmacytosis in the brain is an early constant feature in herpetic encephalitis. It appears at the time of the development of the perivascular cuff. Concomitant with these changes in the brain similar alterations occur in the bone marrow and spleen. The presence of cells of the plasmacytic lineage among the inflammatory cells in the earliest stages of the disease leads to the conclusion that the disease process is a response to an antigen-antibody reaction, hence allergic in nature.