Immunological aspects of immunodeficiency diseases part 57

In contrast, MHC class II deficiency results in a profound failure of CD4 cell functions. Lack of thymic CD4+ CD8- cell selection for survival results in peripheral CD4 lymphopenia. Because CD4 function is required for normal cell-mediated immunity, as well as antibody production, MHC class II deficiency results in a severe form of SCID with a fatal outcome. MHC class II deficiency is due to a mutation in one of four transcription factors (RFXAP, CIITA, RFX5, RFXANK), which regulate MHC class II expression.