T cell activation deficiency associated with an aberrant pattern of protein tyrosine phosphorylation after CD3 perturbation in Down's syndrome.

Children affected by Down's syndrome (DS) have an increased susceptibility to viral or bacterial infections and leukemia, associated with several abnormalities of the immune system. We investigated whether the T cell defect was qualitative in nature and associated with abnormalities of the early events occurring during cell activation. The proliferative response of lymphocytes from DS individuals after CD3 cross-linking was clearly depressed, as already reported. In contrast, phorbol ester and ionomycin were able to induce cell cycle progression in DS, suggesting a defect in the early stages of the signal transduction through a T cell receptor/CD3 (TCR/CD3) complex upstream of protein kinase C activation. The functional impairment in DS was not related either to a decrease of circulating mature-type CD3+ cells, which express high levels of surface of CD3 molecules, or to a decrease of the CD4+ subpopulation. The analysis of phosphotyrosine-containing proteins after the cross-linking of CD3 molecules in DS lymphocytes revealed a partial signaling, characterized by increased phosphorylation of proteins of 42-44 kD, comparable to that observed in control subjects, but not of proteins of 70 and 21 kD. Moreover, although the "anti-anergic" gamma element of IL-2, IL-4, IL-7, and IL-15 receptors was normally tyrosine-phosphorylated during cell activation, the CD3 zeta-associated protein kinase (ZAP-70) was not. Our results indicate that in DS there is a T cell activation defect, characterized by partial signal transduction through a TCR/CD3 complex, and associated with a selective failure of ZAP-70 tyrosine phosphorylation.

Apoptosis as a mechanism of peripheral blood mononuclear cell death after measles and varicella-zoster virus infections in children.

Viral infections may induce an acquired form of immunodeficiency, generally lasting a few weeks. In the more severe form, such as HIV infection, the immunodeficiency is permanent. Programmed death of T cells represents one of the mechanisms by which HIV determines the T cell functional impairment, finally resulting in the destruction of T cells. In this study, we evaluated whether an altered regulation of apoptosis was also implicated in the anergy associated with the common measles or varicella-zoster virus (VZV) infections in infancy. A spontaneous apoptosis of peripheral blood mononuclear cells was observed in children who had suffered from these infections as long as 6 mo after the acute disease. Apoptosis was demonstrated through analysis of cellular DNA content, morphologic evidence of cell nuclei shrinkage, and by analysis of DNA degradation. Stimulation of T cells through anti-CD4 MAb increased the number of apoptotic cells with a maximal effect 72 h after the stimulation. Our results suggest that apoptosis may account for the anergy that follows acute viral infections in infancy.

Combined immunodeficiency phenotype associated with inappropriate spontaneous and activation-induced apoptosis.

Programmed death of T cells has been proposed as one of the mechanisms by which HIV induces a decline in the number and functions of T cells in advanced AIDS. In this study we report on a patient affected by a congenital form of combined immunodeficiency presenting as a profound T cell activation deficiency. Subsequently, a gradual loss of T cells occurred, eventually resulting in a classical form of severe combined immunodeficiency (SCID). In this patient a sizeable fraction of apoptotic cells was documented in the first phase of the disease by either propidium iodide staining or DNA fragmentation analysis. The presence of anergic T cells of maternal origin and engrafted in the child was excluded by analysis of DNA polymorphic regions. At 4 years of age the patient died of disseminated interstitial pneumopathy, while still awaiting an HLA-matched bone marrow transplantation. On the occasion of a new pregnancy in the mother, the prenatal immunological evaluation of the female fetus revealed a T B+ SCID phenotype. This is the first observation of a primary immunodeficiency associated with inappropriate apoptosis.

Defective interleukin-2 production in children with chronic hepatitis B: role of adherent cells.

BACKGROUND: Chronic hepatitis B (CHB) virus infection is associated with functional abnormalities of cell-mediated immunity, defective interferons alpha and gamma synthesis, and interleukin-2 receptor expression. In this study, interleukin-2 (IL-2) production and the role of adherent cells was evaluated in 25 children chronically infected with hepatitis B virus. METHODS: IL-2 activity was measured by bioassay in supernatants of phytohemoagglutinin-stimulated peripheral blood mononuclear cells. In a few patients, IL-2 concentration was also immunochemically determined. Coculture experiments using a mixture of adherent cells and lymphocytes from healthy children and patients with CHB were also performed. RESULTS: Children with CHB showed lower IL-2 production than healthy controls. In patients, IL-2 activity was 34.7 +/- 22.5 U/ml as compared to 152.6 +/- 78.5 U/ml of controls. Immunochemical quantitation of IL-2 confirmed a lower IL-2 production in patients. No correlation was found between the functional T-cell defect and the severity of liver damage, degree of viral replication, and duration of the disease. In co-culture experiments, adherent cells from HBsAg-positive patients inhibited IL-2 production following mitogen stimulation of control non-adherent cells by 67%. The inhibitory effect, mediated by patients adherent cells, was abolished by blocking with indomethacin prostaglandins, that are potent local immunomodulators released by adherent cells. CONCLUSIONS: Our results further support the observation that in children with CHB virus infection adherent cells play an important role in the inappropriate regulation of immune response, an effect being likely mediated by prostaglandins.

Progressive deficiencies in blood T cells associated with a 10p12-13 interstitial deletion.

We report on a 8-year-old patient affected by a selective T-cell defect associated with mental retardation and dysmorphic signs. At birth thymic aplasia and hypoparathyroidism were noted, suggesting a DiGeorge-like anomaly. The immunological evaluation during the 8 years follow-up revealed a progressive decrease of CD3+CD4+ lymphocytes, which paralleled deficiencies of blood T cells. Chromosome analysis using GTL banding revealed an interstitial deletion of the short arm of chromosome 10. We next investigated whether the expression of IL-2R alpha chain and Nil-2-a genes, which are located on the short arm of chromosome 10, was affected by the deletion. Transcription of these two genes was normal, thus suggesting that the two regions were preserved. In situ hybridization studies with the painting libraries #G3A7 and #G9 confirmed that the two regions were preserved and allowed us to define the breakpoint as 10p12-10p13. Due to the similarities between DiGeorge and 10p syndromes, we suggest that the 10p13-10p12 region contains a gene(s) potentially related to gene products of the 22q11 region, frequently altered in patients with DiGeorge.

DNA typing of DQ and DR alleles in IgA-deficient subjects.

IgA deficiency (IgA-D) represents the most common immunodeficiency syndrome of infancy. In most cases IgA-D represents an isolated immunological disorder, while sometimes it is associated with IgG subclass deficiency or with the presence of autoantibodies. We investigated the pattern of association of IgA-D with DRB1 and DQB1 loci of the HLA region by DNA molecular typing, which allows the identification of previously serologically undefined specificities. We also compared the gene frequency of DRB1 and DQB1 allelic variants between IgA-D subjects with or without serum autoantibodies. Our results indicate that the gene frequency of the DRB1*0102 subtype and of the DRB1*0102, DQB1*0501 haplotype is significantly higher in IgA-D than in the general population. Furthermore, the IgA-D subjects with autoantibodies showed a positive association with DR4 and DR13 subtypes, thus supporting the hypothesis that genetic factors are also involved in the association between IgA-D and autoantibodies.