B7-H3 [CD276] (human) ELISA Kit

B7 family of immunoregulatory proteins is composed of ten members: B7-1 (CD80), B7-2 (CD86), B7-H1 (PD-L1), B7-DC (PD-L2), B7-H2, B7-H3, B7-H4, B7-H5 (VISTA), B7-H6 and B7-H7. B7-H3 (or CD276) is a 316aa long type I transmembrane protein. B7-H3 shares 20-27% amino acid identity with other B7 family ligands. Glycosylated B7-H3 protein has a molecular weight of approximately 100 kDa. A B7-H3 'soluble' isoform has been detected in plasma and B7-H3 is also expressed on exosomes.

B7-H3 is ubiquitously expressed by cells in the non-hematopoietic compartment, such as fibroblasts and epithelial cells, it can be induced on T cells and NK cells. Although B7-H3 expression is elevated in tumors, B7-H3 is also constitutively expressed at higher levels in the liver than in other healthy tissue. B7-H3 mRNA is expressed in most normal tissues, but the B7-H3 protein expression is limited in normal tissues, because of its posttranscriptional regulation by miRNAs. Specifically, miRNA-29 suppresses B7-H3 expression in normal tissues by targeting the B7-H3 3'-untranslated mRNA region.

Little is known about the receptors for these B7-family ligands and their downstream signaling. TLT2 (triggering receptor expressed on myeloid cells-like transcript 2) has been characterized as a putative receptor for B7-H3, but it is dispensable for T cell response, suggesting that other unknown receptors should bind B7-H3. Although receptors remain unidentified, soluble B7-H3 has been shown to bind to CD4⁺ T, CD8⁺ T, NK and NKT cells and the extent of its binding is increased upon T cell activation.

B7-H3 inhibits the activation and function of T cells, potently suppressing the proliferation, cytokine production and cytotoxicity of activated T cells. It also inhibits natural killer (NK) cell activation and has a proinflammatory role leading to cytokine release from monocytes and/or macrophages, However, B7-H3 was initially characterized as a co-stimulatory molecule required for optimal promotion of T cell proliferation and cytokine production, which makes the exact role of B7-H3 controversial.

The B7-H3 [CD276] (human) ELISA Kit (Prod. No. AG-45B-0025) detects the soluble human B7-H3 (CD276) protein that is ectopically expressed in various cancers and its levels in serum of patients with cancer suggests it can be used as a noninvasive biomarker for diagnosis, prognosis and/or treatment response.