MICB

MICB Full Name

MHC class I polypeptide-related sequence B

MICB Introduction

MHC Class I Polypeptide-Related Sequence B (MICB) is a stress-inducible cell surface glycoprotein belonging to the MHC class I chain-related (MIC) family. Unlike classical HLA class I molecules, MICB is not polymorphic, does not associate with β2-microglobulin, and is not involved in peptide presentation. Structurally, it possesses α1, α2, and α3 extracellular domains similar to HLA molecules. Its expression is not constitutive but is strongly upregulated by cellular stress, including viral infection (e.g., cytomegalovirus), DNA damage, heat shock, and malignant transformation. This makes MICB a crucial "danger signal" that alerts the immune system to distressed or transformed cells.

Figure 1. Strcuture of MHC class I polypeptide-related sequence B.

Regulation: Shedding and Genetic Factors
The proteolytic release of sMICB from the cell surface is a key regulatory and immune evasion mechanism. This shedding is primarily mediated by A Disintegrin and Metalloproteinases (ADAMs), particularly ADAM9, ADAM10, and ADAM17. Inhibition of these sheddases can restore membrane MICB expression and enhance tumor cell killing. Additionally, genetic variants in the MICB gene have been associated with susceptibility to several infectious and autoimmune diseases, including hepatitis B virus infection outcome and psoriasis, highlighting its broader role in immune regulation.

Clinical Significance and Therapeutic Potential
The MICB/NKG2D axis represents a promising target for immunotherapy. In cancer, strategies aim to block sMICB to restore NKG2D function or to use NKG2D-engaging bispecific antibodies to direct T/NK cells to tumors. It is also a potential target for viral vaccine design to overcome HCMV immune evasion. Furthermore, serum levels of sMICB are being investigated as a diagnostic and prognostic biomarker for various cancers and inflammatory conditions. Enhancing MICB surface expression through pharmacological inhibition of sheddases or induction with epigenetic drugs is another active area of research to bolster anti-tumor immunity.

Alternate Names for MICB

MICB; MHC class I polypeptide-related sequence B; PERB11.2; MIC-B; MHC class I mic-B antigen; stress inducible class I homolog; MHC class I chain-related protein B; MHC class I-like molecule PERB11.2-IMX;