Characterization of B cells in human thymus.

The surface characteristics of B cells present in the human thymus were investigated. Cytofluorometrical and immunohistological studies, using anti-human IgM or anti-B cell monoclonal antibodies (mAbs; anti-Leu 12Ab, anti-Leu 16Ab, or L26), revealed that a small number of B cells are present in the human thymus. The thymic B cells were detected only in a low-density cell population, whereas in a high-density cell fraction, only T cells were found. In 15 cases, all of which the thymi were histologically normal, the percentages of B cells in the low-density fraction were 0.28% to 50% (6.8% in average), and Leu 1+ (CD5+) B cells in the low-density fraction were 0.1% to 26% (3.5% in average); approximately 50% of the thymic B cells were Leu 1+ B cells. These results indicate that B cells, especially Leu 1 (CD5)+ B cells, are also present in the human thymus, as suggested from our previous reports on mice.