Engagement of the Adhesion Receptor CD 22 Triggers a Potent Stimulatory Signal for B Cells and Blocking CD 22 KD 22 L Interactions Impairs T - cell Proliferation

The 6-lymphocyte-restricted adhesion protein CD22 mediates sialic acid-dependent cell-cell interactions. Engagement of CD22 on B lymphocytes with a CD22 monoclonal antibody (MoAb) H622.7 that blocks the binding of CD22 to its ligand(s) directly stimulated 6-cell proliferation. In addition, the HB22.7 MoAb costimulated 6-cell proliferation with either anti-lgM, interleukin-2 (IL-2). IL-4, or CD40 and triggered predominantly B-cell IgG secretion with IL-2. Even more striking levels of B-cell proliferation occurred with HB22.7 MoAb under culture conditions that enhanced B-6-cell interactions. In contrast, a nonblocking CD22 MoAb (CD22.5) poorly costimulated in similar experiments. The functional