human leukocyte antigen (HLA) class II

Cell surface receptors compsed of an alpha and a beta chains and expressed specialised cell types, including dendritic cells, macrophages and B cells (all of which are professional antigen presenting cells APCs), and are encoded by the Major Histocompatibility Complex (MHC) genes located on chromosome 6. There are three sets of genes that encode functional receptors called HLA-DP, -DQ and DR. APCs process soluble antigens such as toxins or other proteins made by bacteria (for example) and then display them on their surface as peptide antigens in combination with HLA Class II molecules. CD4+Helper T cells specific for these antigens are then able to be activated and respond to the presence of the presented peptide derived from the invading bacteria or microbe.

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