INTERLEUKIN-7 RECEPTOR ⍺ CHAIN–DEPENDENT SIGNALING IS REQUIRED FOR T-CELL DEVELOPMENT : Basis for T−B+NK+Severe Combined Immunodeficiencies in Humans - 04/09/11
Résumé |
Severe combined immunodeficiencies (SCIDs) are inherited diseases that represent the most severe forms of primary immunodeficiencies, affecting approximately 1 child out of every 80,000 live births. These diseases are characterized by profound defects in cellular and humoral immunity. As a result, affected individuals typically die within the first year of life because of recurrent opportunistic infections, unless they receive successful bone marrow transplants. SCID is most appropriately described as a syndrome with diverse genetic origins. Because of advances made in genetics and molecular biology, it has become possible to identify the genes responsible for many forms of SCID, although approximately 30% of cases have unknown causes.6, 20, 45
In this article, SCID refers to cases of inherited immunodeficiency characterized by a marked decrease in T cells, as previously defined.20 Patients with other inherited immunodeficiencies, such as those resulting from mutations in the T-cell receptor (TCR)–associated chains, CD3γ or CD3ε, or in the TCR-associated tyrosine kinase ZAP-70, may have normal or decreased numbers of T cells, but typically do not develop life-threatening infections in the first months of life.20 Patients with SCID then can be classified into four groups according to their basic immunologic phenotypes (Table 1). In all four groups, T cells are almost uniformly decreased in numbers; however, the levels of B and natural killer (NK) cells are more variable. In the first group, T, B, and NK cells are all diminished (T−B−NK− SCID). The most severe form in this group is reticular dysgenesis, a disease in which the lymphoid and myeloid systems are affected.18 The responsible gene for this form of SCID has not been identified. Adenosine deaminase (ADA) deficiency is less severe, but still also is characterized by a profound block in lymphocyte maturation.30 Mutations in the ADA gene result in the accumulation of dATP in cells, therefore inhibiting cell division. The major impact of ADA deficiency is in the immune system. In the second group, T and B cells are diminished but NK cells are not (T−B−NK+ SCID). Approximately 20% of all patients with SCID have such a block in T- and B-lymphocyte differentiation because of a defect in the recombination process.83 This group can be divided in two subgroups: one with a normal cell radiosensitivity, resulting from mutations in the RAG1 or RAG2 genes, which are responsible for the initiation of the V(D)J rearrangement process,1, 80 and the other with an increased cell radiosensitivity, in which the involved gene(s) have not been identified.11 The third and fourth groups are characterized by the presence of B cells (T−B+ SCID); however, the B cells are usually nonfunctional, in part because of an absence of T-cell help.13 The third group is characterized by the absence of NK cells (T−B+NK− SCID). The most frequent form of SCID in this group—and indeed the most common overall form of SCID is X-linked SCID (XSCID). In XSCID, which accounts for almost 50% of cases of SCID, patients have profoundly diminished numbers of T cells and NK cells, but normal or increased numbers of B cells.45, 47 XSCID was found to result from mutations in the gene encoding the γ chain of the interleukin-2 (IL-2) receptor.61 As discussed below, IL-2Rγ is now denoted as the common cytokine receptor γ chain, γc, because it is shared by the receptors for IL-2, IL-4, IL-7, IL-9, and IL-15.24, 36, 38, 39, 60, 61, 75, 76, 87 The XSCID phenotype also has been found in patients with an autosomal recessive form of SCID, and it was hypothesized that this form of SCID could result from mutations in the gene coding for the tyrosine kinase Jak3,75 which associates with γc and is activated by IL-2, IL-4, IL-7, IL-9, and IL-15.48 Finally, the fourth group of SCID consists of patients with a selective T-cell defect (T−B+NK+ SCID). One of the genetic causes for this syndrome is defective expression of IL-7R⍺,70 which is the principal focus of this article.
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| Address reprint requests to Warren J. Leonard, MD, Laboratory of Molecular Immunology, National Heart, Lung, and Blood Institute, National Institutes of Health, Building 10, Room 7N252, 9000 Rockville Pike, Bethesda, MD 20892–1674, e-mail: wjl@helix.nih.gov |
Vol 20 - N° 1
P. 51-63 - février 2000 Retour au numéro
Article précédent
- HUMAN INTERLEUKIN-2 RECEPTOR ⍺ DEFICIENCY
- Chaim M. Roifman, Harjit K. Dadi
- DIAGNOSIS AND MANAGEMENT OF INHERITABLE DISORDERS OF INTERFERON-γ–MEDIATED IMMUNITY
- Capucine Picard, Olivier Baud, Claire Fieschi, Jean-Laurent Casanova
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