Question

Genetic deficiency in RAG-1 and genetic deficiency in TAP1 both lead to the same outcome: severe combined immunodeficiency (SCID), in which a patient has an almost completely nonfunctional adaptive immune response and is unable to fight off infections with normally harmless microbial organisms. ​EXPLAIN WHY​ deficiency in these two very different genes has the same clinical outcome. How will RAG-1 deficiency affect the immune system? How will TAP1 deficiency affect the immune system? How are these outcomes similar, and how are they different? Why would they give rise to the same set of medical symptoms?

Answer 1

• RAG1 or RAG2 deficiency causes a form of autosomal recessive T-B-NK+ SCID. It accounts for approximately 4% of all SCID cases. The enormous diversity of specific immunoglobulins/B cell receptors and T cell receptors is generated through a process of V(D)J recombination. RAG deficiency is considered an autosomal recessive disease. The disorder is generally identified in infants. Complete loss-of-function in RAG1/2, the main components responsible for V(D)J recombination activity, produces severe immunodeficiency in humans. Hypomorphic RAG variants can retain partial recombination activity and result in a distinct phenotype of combined immunodeficiency with granuloma and/or autoimmunity (CID-G/A). RAG deficiency can be measured by in vitro quantification of recombination activity.

• TAP, are deficient in some human tumor cells. This suggests that antitumor responses by CD8 T cells provide selection pressure to favor outgrowth of cells with defective processing of tumor Ags. Nonetheless, this evidence is only correlative, and controlled in vivo experiments have been lacking to demonstrate that TAP deficiency promotes survival of tumor cells.

• SIMILARITIES - both are T cell dependent .

  • DISSIMILARITIES- RAG 1 deficiency causes auto immune disease SCID and TAP deficiency causes survival of tumour cells.

• Transporter associated with Antigen Processing 1 is a protein that in humans is encoded by the TAP1 gene.The membrane-associated protein encoded by this gene is a member of the superfamily of ATP-binding cassette (ABC) transporters. ABC proteins transport various molecules across extra- and intra-cellular membranes. ABC genes are divided into seven distinct subfamilies (ABC1, MDR/TAP, MRP, ALD, OABP, GCN20, White). This protein is a member of the MDR/TAP subfamily. Members of the MDR/TAP subfamily are involved in multidrug resistance. The protein encoded by this gene is involved in the pumping of degraded cytosolic peptides across the endoplasmic reticulum into the membrane-bound compartment where class I molecules assemble. Mutations in this gene may be associated with ankylosing spondylitis, insulin-dependent diabetes mellitus, and celiac disease.

  Recombination activating gene 1 also known as RAG-1 is a protein that in humans is encoded by the RAG1 gene.The protein encoded by this gene is involved in antibody and T-cell receptor V(D)J recombination. RAG-1 is involved in recognition of the DNA substrate, but stable binding and cleavage activity also requires RAG-2. The RAG-1/2 complex recognizes recombination signal sequences (RSSs) that flank the V, D and J regions in the genes that encode the heavy and light chains of antibodies and components of T-cell receptors. The complex binds to the RSSs and nicks the DNA. This leads to the removal of the intervening DNA and the eventual ligation of the V, D and J sequences. Defects in this gene can cause several different diseases.