Major histocompatibility complex

The major histocompatibility complex (MHC) is a large cluster of roughly 140 genes, grouped into three classes (I, II and III). The genes code for a set of proteins found on every human cell surface and that allows the immune system to determine whether the cell is foreign, abnormal, or infected.

The best-known MHC genes are the human leukocyte antigen (HLA) genes, found in classes I and II of the MHC. Their main function is to ‘present’ fragments of proteins found within the cell to T-cells. The HLA genes are highly variable. Indeed, the gene HLA-B is the most polymorphic of all human genes known, with over 250 alleles identified.1


  1. Bodmer J et al. Nomenclature for factors of the HLA system, 1995. Tissue Antigens 46: 1-18, 1995
Community Consensus Statement on Access to HIV Treatment and its Use for Prevention

Together, we can make it happen

We can end HIV soon if people have equal access to HIV drugs as treatment and as PrEP, and have free choice over whether to take them.

Launched today, the Community Consensus Statement is a basic set of principles aimed at making sure that happens.

The Community Consensus Statement is a joint initiative of AVAC, EATG, MSMGF, GNP+, HIV i-Base, the International HIV/AIDS Alliance, ITPC and NAM/aidsmap

This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.

NAM’s information is intended to support, rather than replace, consultation with a healthcare professional. Talk to your doctor or another member of your healthcare team for advice tailored to your situation.