Search

A study of mice obtained from embryonic stem (ES) cells mutated at the interleukin 2 receptor gamma chain (IL-2Rgamma) by Cre loxP-mediated recombination shows that IL-2Rgamma mediates the production and activity of mainstream B- and T-cells and also contributes to natural killer (NK)-cell development. The mutant mice deficient in IL-2R gamma show reduced levels of B, T and NK cells. Mutation also attenuates gut-associated intraepithelial lymphocytes and abolishes the Peyer's patches.

Immunofluorescence studies and sequence analysis of the interleukin 2 receptor (IL-2R) gamma chain reveal that a splice site gene mutation in IL-2R gamma causes the release of two IL-2R gamma transcripts that cause a 5-fold reduction in the high-affinity functional expression of IL-2Rs, resulting in X chromosome-linked severe combined immunodeficiency disease. The first transcript has a small intronic insertion while the second one includes a single amino acid substitution. The splice mutation induces the formation of peripheral T-cell clones in the T-cell antigen receptor beta-chain repertoire to cause the development of partial immunodeficiency phenotypes.

Testing for a particular DNA sequence in the CD40 ligand gene may be effective for prenatal diagnosis of X-linked hyper-IgM syndrome. X-linked hyper-IgM syndrome is an inherited immune disorder characterized by recurrent infections, enlarged lymph nodes and a decrease in neutrophilic white blood cells. Researchers performed genetic analyses on blood samples from four families affected by X-linked hyper-IgM syndrome and from 36 healthy women. Genetic analysis was also performed on a chorionic villus sample from a pregnant woman who already had a child with X-linked hyper-IgM syndrome. The CD40 ligand gene was found to be useful for analysis in 80% of the healthy women. A certain DNA sequence was found to be associated with the syndrome in affected patients. The fetus tested by chorionic villus sampling was diagnosed with the syndrome on the basis of the CD40 ligand gene sequence.

The activity of the Src family protein-tyrosine kinase p56lck is regulated by phosphorylation and dephosphorylation of two critical tyrosine residues Tyr394 and Tyr505. Tyr394 is autophosphorylated after p56lck activation, whereas phosphorylation of Tyr505 is believed to be due to p56lck which negatively modulates p56lck activity. To determine whether Tyr505 could be autophosphorylated, we used the prokaryotic glutathione S-transferase expression system to express wild-type Lck, the mutants [Y394F]Lck and [Y505F]Lck, a kinase-deficient p56lck with a mutation of the A-TP-binding site [K273E]Lck and a double mutant [Y394F, Y505F]Lck. We studied the kinase activities and the patterns of autophosphorylation for tyrosine residues in these mutants and wild-type Lck both in vivo and in vitro. Wild-type Lck. [Y505F]Lck and [Y394F]Lck were phosphorylated on tyrosine. Both the kinasedeficient mutant[K273E]Lck and the double mutant [Y394F. Y505F]Lck did not react with monoclonal anti-phosphotyrosine antibody [anti-Y(P) mAb], thus providing evidence that (a) the bacterial strains used lacked intrinsic protein-tyrosine kinase activities, and therefore tyrosine phosphorylations of wild-type Lck, [Y505F]Lck and [Y394F]Lck are due to autophosphorylation occurring in vivo in bacteria, and (b) that p56lck can only be autophosphorylated on two tyrosine residues, namely Tyr394 and Tyr505. Phosphopeptide mapping analysis confirmed that p56lck can undergo autophos-, phorylation tm these two tyrosine residues. We propose that autophosphorylation at Tyr505 of p56lck may represent an accessory mechanism for the down-regulation of the tyrosine kinase activity of p56lck. [ABSTRACT FROM AUTHOR]

Mutant mice where tyrosine 136 of linker for activation of T cells (LAT) was replaced with a phenylalanine (Lat(Y136F) mice) develop a fast-onset lymphoproliferative disorder involving polyclonal CD4 T cells that produce massive amounts of Th2 cytokines and trigger severe inflammation and autoantibodies. We analyzed whether the Lat(Y136F) pathology constitutes a bona fide autoimmune disorder dependent on TCR specificity. Using adoptive transfer experiments, we demonstrated that the expansion and uncontrolled Th2-effector function of Lat(Y136F) CD4 cells are not triggered by an MHC class II-driven, autoreactive process. Using Foxp3EGFP reporter mice, we further showed that nonfunctional Foxp3(+) regulatory T cells are present in Lat(Y136F) mice and that pathogenic Lat(Y136F) CD4 T cells were capable of escaping the control of infused wild-type Foxp3(+) regulatory T cells. These results argue against a scenario where the Lat(Y136F) pathology is primarily due to a lack of functional Foxp3(+) regulatory T cells and suggest that a defect intrinsic to Lat(Y136F) CD4 T cells leads to a state of TCR-independent hyperactivity. This abnormal status confers Lat(Y136F) CD4 T cells with the ability to trigger the production of Abs and of autoantibodies in a TCR-independent, quasi-mitogenic fashion. Therefore, despite the presence of autoantibodies causative of severe systemic disease, the pathological conditions observed in Lat(Y136F) mice unfold in an Ag-independent manner and thus do not qualify as a genuine autoimmune disorder.