MHC Class 2 Major histocompatibility complex class<unk>  proteins are important because under normal function they have important responsibility in the human body's immune system response. MHC<unk>  proteins present exogenous antigens that activate CD4+ T-lymphocytes, immune cells that are responsible for activating other immune cells like CD8+ T-lymphocytes and macrophages. MHC<unk>  proteins are also important for positive and negative selection in the thymus because they present antigens to immature T-cells, allowing the T cells to differentiate into proper functioning CD4+ T-lymphocytes. This may explain why patients with BLS<unk>  display decreased levels of CD4+ T-lymphocytes in their blood. The basis for BLSII is not due to defects in the MHC<unk>  genes themselves, it is the result of mutations in genes that code for proteins, transcription factors that normally regulate the expression of the MHC<unk>  genes. One of the several proteins that are required to switch on MHC<unk>  genes in various cells<unk> s is absent.
Bare lymphocyte syndrome type II
Kasabach–Merritt syndrome
Pitt–Hopkins syndrome
Hypotrichosis–lymphedema–telangiectasia syndrome
Schwartz–Jampel syndrome
EAST syndrome
Rapp–Hodgkin syndrome
Hagemoser–Weinstein–Bresnick syndrome