B7h3 ELISA Kits

The human B lymphocyte activation antigen B7 provides regulatory signals for T lymphocytes as a consequence of binding to its ligands CD28 and CTLA-4. The cDNA for B7 has previously been isolated and predicted to encode a type I membrane protein. It is expressed on activated B cells and y-interferon (y-1FN)-stimulated monocyte. The B7 antigen is the natural ligand for CD28 on T cells. After the engagement of T-cell receptor with antigen in association with major histocompatibility complex (MHC) class 11, a second signal mediated through the binding of B7 to CD28 greatly upregulates the production of multiple lymphokines, including interleukin-2 (IL-2), y-INF, tumor necrosis factor-a (TNF-a), and granulocytemacrophage colony-stimulating factor (GM-CSF). Also, B7 expression was confined to several histologically defined subgroups of B cell malignancies. The majority of non-Hodgkin's lymphomas were B7+ whereas the B cell leukemias and circulating non-Hodgkin's lymphomas were generally negative. These results demonstrate that B7 expression is limited to normal activated B cells and noncirculating B cell malignancies.

After in vitro activation of B cells, the B7 protein is first detected on the cell surface at 24 hours, peaks at 72 hours, and declines thereafter. B7-positive B cells isolated from human lymphoid tissues do not proliferate in response to growth factors alone; however, after Ig crosslinking, these cells more rapidly enter S phase than B7-negative cells. By its induction on activated B cells and y-IFNstimulated monocytes and subsequent engagement with CD28, B7 may play a critical role in the amplification of the immune response by regulating T-cell activation and lymphokine synthesis.