Question

People with a deficiency in the TAP, transporter for antigen processing, have partial immunodeficiency as well as autoimmune manifestations. You see both immune deficiency and autoimmunity in people with this disorder, why?

Answer 1

Antibodies from the humoral branch of the immune system deal with extracellular viruses and bacteria, whereas the cellular immune system identifies and eliminates infected and malignant cells. To enable the recognition, MHC class 1 (major histocompatibility complex) molecules present peptides on the cell surface.

The delivery of these peptides to ER (endoplasmic reticulum) and then loading on to the MHC class I molecules is performed by the transporter associated with antigen processing (TAP).

Deficiency in TAP function can lead to a loss of expression of MHC class I molecules on the cell surface. This can lead to escape of tumors and virus-infected cells from immune surveillance which can, in turn, lead to both immunodeficiency and autoimmunity.