CD5-positive B-cells of the fetal and adult spleen lymphoid tissue: an immunophenotypical study.

The lymphoid tissue of the human fetal spleen at various stages of gestation was studied on frozen and paraffin sections and with two-colour flow cytometry. On the sections scattered lymphoid cells and perivascular lymphoid aggregates were found starting from the 15th week of gestation. CD3, CD5, CD19, CD20, CD21, CD22, CD24, CD35, CD38-positive cells were observed. No CD10- and CD23-positive cells were detected. Flow cytometry showed a prevalence of B-lymphocytes. The majority of them expressed CD5 antigen. These cells were also IgM/D, CD19, CD20, CD21, CD22, CD24 and CD35-positive. Only few of them expressed CD10 and CD23. A similar phenotype was found in human cord blood. By contrast, in adult spleens CD5 B-cells never exceeded 8% of the B-cells. The comparison between CD5 B-cells of fetal spleen and CD5 B neoplastic cells of 72 cases of small B-cell lymphomas showed that CD23, which was usually expressed by a high percentage of the neoplastic cells, particularly in B-CLL, was not displayed by the majority of the CD5 non neoplastic cells. The reverse was shown by CD35. These findings suggest that different states of activation distinguish the normal CD5 B-cells from their malignant counterpart.