A ZAP-70 kinase domain variant prevents thymocyte-positive selection despite signalling CD69 induction

Response of mouse thymic cells to radiation after transfusion of mesenchymal stem cells

Thymic lymphoma is a highly invasive and even metastatic cancer. This study investigated the effects of mesenchymal stem cells (MSCs) transfusion on cell cycle, cell proliferation, CD3 expression, mutation frequency of T cell receptor using mouse model of thymic lymphoma.C57BL/6J young mouse models of thymoma were injected with MSCs. Six months later, the thymus was taken for pathological examination and flow cytometry studies. The cells were labeled with anti-CD4, CD8, CD3, propidium iodide, or CFDA-SE, cell cycle, proliferation kinetics, and mutation frequency of T cell receptor, respectively.Pathologic results showed that control had clear corticomedular structure with regularly shaped lymphocytes. After radiation, the thymus structure was completely destroyed, with lymphoid tumor cells diffusely distributed and heavily stained, and large nuclei. Transfusion of MSCs resulted in normal thymus structure. Cytometry studies showed that there were more CD4-/CD8- T cells in the thymus of irradiated mice than in control; transfusion of MSCs led to reduced CD4-/CD8- T cells. In irradiated mice, there were less CD4+/CD8+ T cells than in control and MSCs transfusion groups. It was observed that there were more cells arrested in G1 phase in the thymus cells and CD4-/CD8- T cells in irradiated mice than in other 2 groups, whereas there were more cells arrested in S phase in CD4+/CD8+ and CD4+/CD8- T cells in irradiated mice than in the other mice. In the thymus cells, and CD4+/CD8+ and CD4+/CD8- T cells, irradiated mice group had significantly less parent, G2, G3, and G4 cells, and more cells at higher generations, and also higher proliferation index. In CD4-/CD8- T cells, irradiated mice had significantly more parent, G2, and G3 cells, and less G4, G5, G6, and propidium iodide, as compared with the other 2 groups. The expression of CD3 in CD4/CD8 T cells was significantly higher than in control. MSCs transfusion improved CD3 expression, but was still less than the control. Irradiation resulted in very high mutation frequency of T cell receptor, which was barely affected by MSCs transfusion.Mesenchymal stem cell transfusion is able to restore the cell cycle and cell proliferation, but not CD3 expression and mutation frequency of T cell receptor in irradiated mice to control level.

Quantitative reduction of the TCR adapter protein SLP-76 unbalances immunity and immune regulation

Gene variants that disrupt TCR signaling can cause severe immune deficiency, yet less disruptive variants are sometimes associated with immune pathology. Null mutations of the gene encoding the scaffold protein Src homology 2 domain-containing leukocyte protein of 76 kDa (SLP-76), for example, cause an arrest of T cell positive selection, whereas a synthetic membrane-targeted allele allows limited positive selection but is associated with proinflammatory cytokine production and autoantibodies. Whether these and other enigmatic outcomes are due to a biochemical uncoupling of tolerogenic signaling, or simply a quantitative reduction of protein activity, remains to be determined. In this study we describe a splice variant of Lcp2 that reduced the amount of wild-type SLP-76 protein by ~90%, disrupting immunogenic and tolerogenic pathways to different degrees. Mutant mice produced excessive amounts of proinflammatory cytokines, autoantibodies, and IgE, revealing that simple quantitative reductions of SLP-76 were sufficient to trigger immune dysregulation. This allele reveals a dose-sensitive threshold for SLP-76 in the balance of immunity and immune dysregulation, a common disturbance of atypical clinical immune deficiencies.

A novel Zap70 mutation with reduced protein stability demonstrates the rate-limiting threshold for Zap70 in T-cell receptor signalling

Loss of ζ-associated protein 70 (Zap70) results in severe immunodeficiency in humans and mice because of the critical role of Zap70 in T-cell receptor (TCR) signalling. Here we describe a novel mouse strain generated by N-ethyl-N-nitrosourea mutagenesis, with the reduced protein stability (rps) mutation in Zap70. The A243V rps mutation resulted in decreased Zap70 protein and a reduced duration of TCR-induced calcium responses, equivalent to that induced by a 50% decrease in catalytically active Zap70. The reduction of signalling through Zap70 was insufficient to substantially perturb thymic differentiation of conventional CD4 and CD8 T cells, although Foxp3(+) regulatory T cells demonstrated altered thymic production and peripheral homeostasis. Despite the mild phenotype, the Zap70(A243V) variant lies just above the functional threshold for TCR signalling competence, as T cells relying on only a single copy of the Zap70(rps) allele for TCR signalling demonstrated no intracellular calcium response to TCR stimulation. This addition to the Zap70 allelic series indicates that a rate-limiting threshold for Zap70 protein levels exists at which signalling capacity switches from nearly intact to effectively null.