Subpopulations of B lymphocytes in germinal centers, II. A germinal center B cell subpopulation expresses sIgD and CD23.

To understand B cell development in germinal centers, it is important to delineate the expression of surface antigens among germinal center cells. Because it is unclear whether germinal center cells express common antigens such as sIgD and CD23, we studied their expression among tonsillar lymphocytes with flow cytometry, immunohistochemistry, and in vitro stimulation. Upon studying a large number of tonsils with flow cytometry, we found that occasional tonsils have a very large number of sIgD+ cells among their PNA+ cells. Furthermore, the occasional tonsils with a large number of sIgD+ and PNA+ cells also have many CD23+ cells among their PNA+ cells. Tonsil sections stained immunohistochemically revealed germinal centers containing sIgD+ cells. In addition, PNA- and sIgD+ cells can be induced to express PNA binding sites in vitro without losing the expression of sIgD. Taking these findings together, we conclude that a subpopulation of germinal center B cells coexpresses sIgD and CD23.