The CR2 receptor (CD21) shows increased expression in the more differentiated cells of an antigen-specific B cell line.

Abstract The complement receptor 2 (CR2; CD21), a 145,000 MW glycoprotein, has been useful as a marker of B lymphocyte maturation. It is expressed on the 1:13 monoclonal, EBV-transformed, B cell line which produces TNP-specific IgM-κ and displays an in vitro capacity for differentiation. The line expresses the CD20 + CD21 + phenotype. We studied whether CR2 receptor surface expression varied in relation to the cell cycle or state of differentiation in the 1:13 line. High CD21 and IgM expression occurred in the G 1 phase of the cell cycle. In contrast to CD21, there were no distinctly brighter subpopulations of CD20 positive cells in the G 1 , S, or G 2 M compartments of the cell cycle. When sorted according to size, smaller cells were predominantly in G 1 , whereas a greater proportion of the larger cells were in the G 2 M phase of the cell cycle. The smaller 1:13 cells expressed more CD21 surface antigen and IgM than the larger cells. Cells which formed stable rosettes with TNP-SRBC expressed more surface IgM and CD21 antigen than nonrosetting cells. We have previously shown that the TNP-SRBC rosetting cells were more differentiated, resided in G 1 , and secreted more immunoglobulin than the nonrosetting cells. Thus increased CR2 expression occurred in the more differentiated cells of this human monoclonal B cell line.