CHARACTERIZATION OF NOVEL COSTIMULATORY MOLECULES - A PROTEIN 38-42 KDA FROM B-CELL SURFACE IS CONCERNED WITH T-CELL ACTIVATION AND DIFFERENTIATION

Optimal activation of T cells often requires signals delivered by the ligation of T cell receptor (TcR) and those resulting from costimulato ry interaction between certain T cell surface accessory molecules and their respective counter receptors on antigen presenting cells. The mo lecular events underlying the co-stimulatory activity are still not un derstood fully. Here we describe a 38-42-kDa (B3) protein, present on the surface of lipopolysaccharide-activated B cells, which can provide costimulation to resting T cells leading to a predominant release of interleukin (IL)-4 and IL-5 and negligible amounts of IL-2 and interfe ron-gamma. Binding assay and electron microscopic autoradiography data suggest that this molecule binds T cells, and the same can be compete d by unlabeled B3. Characterization experiments point out that B3 show s up as a single prominent peak on reverse phase-high performance liqu id chromatography, runs as a single spot in reducing two dimensional g el electrophoresis, and is a phosphoglycoprotein. The Western analysis indicate that it does not cross-react with antibodies directed agains t murine ICAM-1, LFA-1 alpha, VCAM-1, HSA, and B7 suggesting the novel ty of the protein. The internal amino acid sequence of this molecule s uggests that it does not belong to a known category of murine B cell s urface molecules.