Mutations in the common gamma chain (γ c , CD132, encoded by the IL2RG gene) can lead to B + T − NK − X-linked severe combined immunodeficiency, as a consequence of unresponsiveness to γc-cytokines such as interleukins-2, -7 and -15. Hypomorphic mutations in CD132 may cause combined immunodeficiencies with a variety of clinical presentations. We analyzed peripheral blood mononuclear cells of a 6-year-old boy with normal lymphocyte counts, who suffered from recurrent pneumonia and disseminated mollusca contagiosa. Since proliferative responses of T cells and NK cells to γc -cytokines were severely impaired, we performed IL2RG gene analysis, showing a heterozygous mutation in the presence of a single X-chromosome. Interestingly, an IL2RG reversion to normal predominated in both naïve and antigen-primed CD8 + T cells and increased over time. Only the revertant CD8 + T cells showed normal expression of CD132 and the various CD8 + T cell populations had a different T-cell receptor repertoire. Finally, a fraction of γδ + T cells and differentiated CD4 + CD27 − effector-memory T cells carried the reversion, whereas NK or B cells were repeatedly negative. In conclusion, in a patient with a novel IL2RG mutation, gene-reverted CD8 + T cells accumulated over time. Our data indicate that selective outgrowth of particular T-cell subsets may occur following reversion at the level of committed T progenitor cells. A reversion of an IL2RG mutation in combined immunodeficiency
Primary immunodeficiencies consist to a large extent of B cell defects, as indicated by inadequate Ab levels or response upon immunization. Many B cell defects have not yet been well characterized. Our objective was to create reliable in vivo and in vitro assays to routinely analyze human B cell differentiation, proliferation, and Ig production and to define reference ranges for different age categories. The in vitro assays were applied to classify the developmental and/or functional B cell defects in patients previously diagnosed with common variable immunodeficiency. Apart from standard immunophenotyping of circulating human B cell subsets, an in vitro CFSE dilution assay was used for the assessment of proliferative capacity comparing T cell–dependent and T cell–independent B cell activation. Plasmablast/plasma cell differentiation was assessed by staining for CD20, CD38, and CD138, and measurement of in vitro Ig secretion. At young age, B cells proliferate upon in vitro activation, but neither differentiate nor produce IgG. These latter functions reached adult levels at 5 and 10 y of age for T cell–dependent versus T cell–independent stimulations, respectively. The capacity of B cells to differentiate into plasmablasts and to produce IgG appeared to be contained within the switched memory B cell pool. Using these assays, we could categorize common variable immunodeficiency patients into subgroups and identified a class-switch recombination defect caused by an UNG mutation in one of the patients. We defined age-related reference ranges for human B cell differentiation. Our findings indicate that in vivo B cell functionality can be tested in vitro and helps to diagnose suspected B cell defects.
A novel role for human neutrophilic granulocytes was recently described, showing that these cells, upon entering the spleen, can be reprogrammed into a distinct B cell-helper neutrophil phenotype that is capable of eliciting B cell responses such as immunoglobulin secretion, class switch recombination and somatic hypermutation. Using similar protocols, we detected a homogeneous population of CD15highCD16high neutrophils in fresh human spleen samples, which did not differ in phenotype and function from blood neutrophils. No phenotypic characteristics of costimulatory nature were detected on splenic or circulating neutrophils, nor could we reproduce the immunoglobulin production of splenic B cells in the presence of splenic neutrophils, although B cell function and neutrophil activity were normal. Independent confirmation of a role for NBH cells is required.
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