Recombinant Human B7-H3 His-tag Avi-tag Protein, CF

Human B7 homolog 3 (B7-H3) is a member of the B7 family of immune proteins that provide signals for the regulation of immune responses (1 - 3). Other family members include B7-1, B7-2, B7-H1/PD-L1, B7-H2, and PD-L2. B7 family proteins are type I transmembrane immunoglobulin (Ig) superfamily members that contain extracellular Ig V‑like and Ig C‑like domains with a short cytoplasmic tail. Among the family members there is about 20 - 40% amino acid (aa) sequence identity. B7-H3 was initially reported to be a 316 aa type I transmembrane precursor protein that contained a signal sequence, an extracellular region with one V‑type and one C‑type Ig domain, a transmembrane segment and a short cytoplasmic tail (1). Subsequent studies have identified a second 110 kDa form whose precursor is 534 aa in length. Termed 4IgB7-H3 or B7-H3b, this molecule has two additional Ig-like domains (one V‑type and one C‑type) and shows a ubiquituous expression pattern (4, 5). It would appear that the human 4Ig form is the principal, if not the only form of B7-H3 (5). Its precursor contains a 26 aa signal sequence, a 435 aa extracellular region, a 31 aa transmembrane domain, and a 42 aa cytoplasmic tail. The four Ig-like domains alternate between V‑type and C‑type, and apparently are the consequence of a V‑C type tandem duplication (4, 5). B7-H3b is expressed on dendritic cells as well as activated T, B and NK cells (5). The mouse gene differs from that of human in that it cannot code for four Ig-like domains; only a V‑type:C‑type pair (4). Human B7-H3b binding to an undefined receptor has shown to be inhibitory to NK cells and cytokine release (6). It also seems to be required for late stage osteoblast differentiation (7).