High expression of CD23 in the proliferation centers of chronic lymphocytic leukemia in lymph nodes and spleen.

Chronic lymphocytic leukemia (CLL) is a B-cell neoplasm composed of a heterogeneous mixture of cells, including small lymphocytes, prolymphocytes, and large transformed cells; these last cells appear to represent the proliferating compartment. CLL cells express, in addition to B cell markers, the transmembrane receptor CD23. CD23 functions as the receptor for IgE and also appears to play a role in controlling the growth and proliferation of lymphocytes. Its level of expression among the different cells in CLL has not been examined. In this study, we show that CD23 expression is much higher in the large transformed CLL cells than in the small lymphoid population. This may provide an explanation for the observed correlation between a circulating CD23 cleavage product (soluble CD23) and prognosis in CLL. In addition, we have shown that proliferation in splenic CLL occurs preferentially in the white pulp zones, even in cases in which both the white and red pulp are extensively infiltrated.