The Expression of the CD21 Antigen in Non-Hodgkin’s Lymphoma Is Involved in LFA-1 Expression and Tumor Survival.

CD21/complement receptor type 2 is a membrane protein expressed on B lymphocytes, follicular dendritic cells, early thymocytes, and a subset of mature T lymphocytes. This major B cell antigen appears later than CD19 and CD20 in cell differentiation and is lost from the cell surface during the early stages of B cell activation. CD21 is characterized not only as a complement ligand but also as an adhesion molecule of the cell surface that is dependent on CD23 expression, suggesting that it may be involved in lymphocyte trafficking and several immune responses. Recently two groups have reported that CD21 expression is significantly negatively associated with mortality in diffuse large B cell lymphomas. From these reports and clinical observations, we have transfected the CD21 gene into a CD21/CD23-negative lymphoma cell line (Namalwa). Interestingly, all established CD21+ transfectants (six clones from different bulks) showed homotypic aggregation during in vitro cell culturing, and none of the anti-CD21 antibodies prevented this cell aggregation. Moreover, these CD21+ transfectants were easily rejected in vivo when they were injected in nude mice compared to vector-only transfectants and parental cells as controls. These observations suggest that other adhesion molecules may be involved in CD21-induced cell aggregation and reduced tumorgenesis in vivo. After the screening of several integrins, CD21+ transfectants highly expressed LFA-1 (CD11a/CD18) on their cell surfaces compared to vector-only transfectants and parental cells. CD21+ transfectants displayed tight adhesion when in contact with recombinant human ICAM-1, and cell aggregation of CD21+ transfectants was blocked by an anti-LFA-1 monoclonal antibody. Northern and Western analysis and confocal laser scanning microscopic analysis suggested that the CD21 expression made the transfer of LFA-1 from the cytoplasm to the cell surface. We conclude that the expression of the CD21 molecule is strongly associated with the LFA-1 expression on the cell surface, independent of the CD23 molecule, and this phenomenon may be involved in tumor survival in non-Hodgkin’s lymphoma in vivo.