Expression of the CD2 molecule on human B lymphoid progenitors.

CD2 expression on human B lymphoid progenitor cells was examined. By immunofluorescence analysis, a small fraction of bone marrow B cells was found to express CD2 on their surface. CD2 expression was not demonstrated on peripheral B cells. Epstein-Barr virus-transformed B cell lines derived from fetal liver at 8 weeks of gestation were analyzed to delineate the expression and function of CD2 at the early stage of human B cell development. Characterization of surface and genomic phenotypes of cell lines revealed that the established cell lines represent at least three different phenotypic characteristics of early B lineage cell: B progenitor, pre B, or early B cell. None of the 18 cell lines and 13 subclones with the phenotype of the early B lymphoid cells initially expressed CD2 antigen. However, CD2 expression was induced by the successive cultivation of some cloned B progenitor cell lines. In spite of the expression of CD2, these clones cell lines were unable to form rosettes with sheep red blood cells. By immunoprecipitation analysis, an identical 50 kDa protein was precipitated with anti-CD2 antibody from the lysates of the radioiodinated CD2+B progenitor cell line and peripheral blood T cells. Anti-CD2 antibody induced significant enhancement of proliferation of the CD2+B progenitor subline. These data indicate that human CD2 is expressed on a fraction of B lineage cells at a very early differentiation stage and may play a role in B lymphopoiesis.