The major histocompatibility complex (MHC) is responsible for binding peptide fragments arising from pathogens in order to display them on the cell surface for recognition from immune cells. Once recognized, the foreign pathogen is typically evaded. The MHC complex is broken into two categories, MHC Class I proteins and MHC Class II proteins. MHC complex I and II proteins are all very different and contain specific molecules to bind different peptides – in fact, they have been described as the most polymorphic genes there are.
Integrins are transmembrane receptors composed of alpha and beta chains, where beta-integrins are mainly expressed in leukocytes. Leukocytes are white blood cells that act in the immune system to defend our body against foreign pathogens.
CD20 is a human B-lymphocyte surface molecule that spans the membrane four times and is expressed on both normal and malignant cells. The CD20 antigen displays a unique expression pattern among hematopoietic cells - it is present on human pre B-lymphocytes and B-lymphocytes at all stages of maturation (except for plasma cells). Low CD20 antigen expression levels have been detected on normal T-lymphocytes. It functions as a B-cell activation receptor and B-lymphocyte development and differentiation agent, presumably through modulating intracellular calcium levels.
The T-cell co-receptor CD8 is a cell-surface glycoprotein that bridges the lipid bilayer by interacting externally with ligands, such as major histocompatibility complex (MHC) class I, as well as internally with signaling molecules such as tyrosine kinase p56 lck. CD8 associates with lck through a zinc clasp structure and down regulates major Th2-type cytokine production.
CD4 is a member of the cluster of differentiation family of proteins, mainly expressed on the surface of thymocytes and a specific subset of mature T-cells. CD4 antibody studies have also shown it expressed on monocytes, cortical cells, microglial cells, dendritic cells and macrophages. The CD4 antibody is widely used in cell marker studies, CD4 being one of the most common CD markers in use.