Phenotypic expression of B-lymphocytes. 2. Immunoglobulin expression of germinal center cells.

With a sensitive and specific immunohistochemical technique, immunoglobulin expression was examined in germinal centers with frozen and paraffin-embedded tissues. The majority of cells positive for surface immunoglobulin (IgM and IgD) were confined to the dark zone of the germinal center, while the cells positive for cytoplasmic immunoglobulin (IgM and IgG) were found in the light zone. There were considerable numbers of germinal center cells without identifiable immunoglobulin. The results, in conjunction with previous in vitro and in vivo B-cell activation studies, indicate that centroblasts (noncleaved cells) are formed during early stages of B-cell differentiation. Centroblasts further mature into centrocytes.