IMMUNOLOGY

Detailed explanation-1: -major histocompatibility complex (MHC), group of genes that code for proteins found on the surfaces of cells that help the immune system recognize foreign substances. MHC proteins are found in all higher vertebrates. In human beings the complex is also called the human leukocyte antigen (HLA) system.

Detailed explanation-2: -Major histocompatibility complex (MHC) class II molecules are cell-surface glycoproteins that play a central role in the immune system by presenting peptides to the antigen receptor of CD4+ T cells.

Detailed explanation-3: -Classical MHC class I molecules are ubiquitously expressed on all mammalian cells including cells of epithelial origin while MHC class II molecules are selectively expressed on antigen-presenting cells (APC) including dendritic cells (DC), macrophages, and B cells.

Detailed explanation-4: -While MHC class I is ubiquitously expressed by almost all cells, MHC class II is mostly expressed by antigen-presenting cells (APCs) such as monocytes, macrophages, and dendritic cells.