Severe combined immunodeficiency is seen with?
Ans. (c) BothRef: Harrison 19th ed. / 2107X-lined severe combined immunodeficiencyMost cases of SCID are due to mutations in the gene encoding the common gamma chain (Yc) a protein that is shared by the receptors for interleukins IL-2, IL-4, IL-7, IL-9, IL-15.These interleukins and their receptors are involved in the development and differentiation of T and B cells.Since the common gamma chain is shared by many interleukin receptors, mutations that result in a non-functional common gamma chain cause widespread defects in interleukin signalling.The result is a near complete failure of the immune system to develop and function, with low or absent T cells and NK cells and non- functional B cells.Adenosine deaminase deficiencyThe second most common form of SCID after X-SCID is caused by a defective enzyme, adenosine deaminase (ADA), necessary for the breakdown of purines. Lack of ADA causes accumulation of dATP. This metabolite will inhibit the activity of ribonucleotide reductase, the enzyme that reduces ribonucleotides to generate deoxyribonucleotides.The effectiveness of the immune system depends upon lymphocyte proliferation and hence dNTP synthesis. Without functional ribonucleotide reductase, lymphocyte proliferation is inhibited and the immune system is compromised.
Pre B- Cell
Pre T Cell
Both
NK Cell
Blood