Linked SCID

X-linked SCID is caused by mutations in the gene encoding the common y (y) chain shared by the receptors for the interleukins IL-2, IL-4, IL-7, IL-9, and IL-15 (see Chapters 4 and 9). X-linked SCID is characterized by impaired maturation of T cells and NK cells and greatly reduced numbers of mature T cells and NK cells, but the number of B cells is usually normal or increased. The humoral immunodeficiency in this disease is due to a lack of T cell help for antibody production. This disease is a result of the inability of the lymphopoietic cytokine IL-7, whose receptor uses the yc chain for signaling, to stimulate the growth of immature thymocytes. In addition, the receptor for IL-15, which is a potent stimulus for the proliferation of NK cells, also uses the yc signaling chain, and the failure of IL-15 function accounts for the deficiency of NK cells.

Heterozygous females are usually phenotypically normal carriers, whereas males who inherit the abnormal X chromosome manifest the disease. Because developing cells in females randomly inactivate one of the two X chromosomes, the normal allele encoding a functional yc protein will not be expressed in half the lymphocyte precursors in a female carrier. These cells will fail to mature, and consequently, all the mature lymphocytes in a female carrier will have inactivated the same X chromosome (carrying the mutant allele). In contrast, half of all nonlymphoid cells will have inactivated one X chromosome, and half the other. A comparison of X chromosome inactivation in lymphoid cells versus nonlymphoid cells may be used to identify carriers of the mutant allele. The nonrandom use of X chromosomes in mature lymphocytes is also characteristic of female carriers of other X-linked mutations of genes that affect lymphocyte development, as discussed later.

Was this article helpful?

0 0
How To Bolster Your Immune System

How To Bolster Your Immune System

All Natural Immune Boosters Proven To Fight Infection, Disease And More. Discover A Natural, Safe Effective Way To Boost Your Immune System Using Ingredients From Your Kitchen Cupboard. The only common sense, no holds barred guide to hit the market today no gimmicks, no pills, just old fashioned common sense remedies to cure colds, influenza, viral infections and more.

Get My Free Audio Book


Post a comment