Miguel Muñoz-Ruiz

TCR signal strength controls thymic differentiation of discrete proinflammatory [gamma][delta] T cell subsets

The mouse thymus produces discrete γδ T cell subsets that make either interferon-γ (IFN-γ) or interleukin 17 (IL-17), but the role of the T cell antigen receptor (TCR) in this developmental process remains controversial. Here we show that Cd3g+/− Cd3d+/− (CD3 double-haploinsufficient (CD3DH)) mice have reduced TCR expression and signaling strength on γδ T cells. CD3DH mice had normal numbers and phenotypes of αβ thymocyte subsets, but impaired differentiation of fetal Vγ6+ (but not Vγ4+) IL-17-producing γδ T cells and a marked depletion of IFN-γ-producing CD122+ NK1.1+ γδ T cells throughout ontogeny. Adult CD3DH mice showed reduced peripheral IFN-γ+ γδ T cells and were resistant to experimental cerebral malaria. Thus, TCR signal strength within specific thymic developmental windows is a major determinant of the generation of proinflammatory γδ T cell subsets and their impact on pathophysiology.

Human CD3γ, but not CD3δ, haploinsufficiency differentially impairs γδ versus αβ surface TCR expression

BackgroundThe T cell antigen receptors (TCR) of αβ and γδ T lymphocytes are believed to assemble in a similar fashion in humans. Firstly, αβ or γδ TCR chains incorporate a CD3δε dimer, then a CD3γε dimer and finally a ζζ homodimer, resulting in TCR complexes with the same CD3 dimer stoichiometry. Partial reduction in the expression of the highly homologous CD3γ and CD3δ proteins would thus be expected to have a similar impact in the assembly and surface expression of both TCR isotypes. To test this hypothesis, we compared the surface TCR expression of primary αβ and γδ T cells from healthy donors carrying a single null or leaky mutation in CD3G (γ+/−) or CD3D (δ+/−, δ+/leaky) with that of normal controls.ResultsAlthough the partial reduction in the intracellular availability of CD3γ or CD3δ proteins was comparable as a consequence of the mutations, surface TCR expression measured with anti-CD3ε antibodies was significantly more decreased in γδ than in αβ T lymphocytes in CD3γ+/− individuals, whereas CD3δ+/− and CD3δ+/leaky donors showed a similar decrease of surface TCR in both T cell lineages. Therefore, surface γδ TCR expression was more dependent on available CD3γ than surface αβ TCR expression.ConclusionsThe results support the existence of differential structural constraints in the two human TCR isotypes regarding the incorporation of CD3γε and CD3δε dimers, as revealed by their discordant surface expression behaviour when confronted with reduced amounts of CD3γ, but not of the homologous CD3δ chain. A modified version of the prevailing TCR assembly model is proposed to accommodate these new data.

Enrichment of the rare CD4+ γδ T-cell subset in patients with atypical CD3δ deficiency

demonstrate the novel finding that human ILC2s highly express the signaling lymphocyte activation molecule family member CD84, although this expression is not selective for ILC2s. Allergen challenge did not increase levels of CD84 expression on ILC2s or CD4 cells. We next assessed the percentage of CRTH21 ILC2s in the peripheral blood of cat-allergic subjects before and 4 hours after nasal cat allergen or diluent challenges (Fig 2). The baseline percentage of CRTH21 cells within the lineage-negative population was 10.7 6 1.9 and 12.0 6 1.3 at the diluent and cat allergen challenge visit, respectively (Fig 2, B). Four hours after diluent challenge, the percentage of CRTH21 cells did not change significantly (9.7 6 1.8) compared with time zero. However, after cat allergen challenge, the percentage of CRTH21 cells nearly doubled to 19.1 6 2.6 compared with baseline (P5 .05) and compared with diluent challenge at 4 hours (P < .05) (Fig 2, B). Thus, nasal cat allergen challenge induced an increased percentage of peripheral blood CRTH21 ILC2s when measured 4 hours after challenge. ILC2s produce large amounts of IL-5 and IL-13 in response to IL-25, IL-33, TSLP, and LTD4 and could initiate and/or propagate allergic airway inflammation. Our studies demonstrate that the percentage of CRTH21 ILC2s in the peripheral blood is rapidly increased (within 4 hours) after allergen challenge. Potential mechanisms for the increase in ILC2s in the peripheral blood may be due to enhanced recruitment of ILC2s from the bone marrow triggered by either humoral (cytokine, chemokine, or mediator production in the nose) and/or cellular mechanisms (cells released from the nasal mucosa trafficking to the bone marrow). The human ILC2 marker CRTH2 is the receptor for prostaglandin D2 (PGD2), a lipid mediator that has a known role in chemotaxis and activation of immune cells. Importantly, a previous study demonstrated that high levels of serum 9a,11b-PGF2, the major PGD2 metabolite, are induced within 5 minutes after airway allergen challenge, suggesting that PGD2 is rapidly available systemically for the recruitment of CRTH21 cells after allergen exposure. We have also recently determined that PGD2 induces chemotaxis of CRTH21 human blood ILC2s in vitro, suggesting that PGD2 may directly regulate the migration of human ILC2s into tissues. The role of increased peripheral blood ILC2 numbers after allergen challenge is unclear. One hypothesis is that greater ILC2 availability in the blood (within 4 hours after challenge) may result in greater numbers of cytokine-producing nasal mucosa ILC2s at later time points, but this would need to be investigated in future studies. Strategies to inhibit the recruitment of ILC2s in allergic individuals may reduce tissue TH2 cytokine levels that contribute to allergic inflammation.

γδ T Lymphocytes in the Diagnosis of Human T Cell Receptor Immunodeficiencies.

Human T cell receptor (TCR) immunodeficiencies (TCRID) are rare autosomal recessive disorders caused by mutations affecting TCR, CD3, or CD247 chains, which share developmental, functional, and TCR expression defects (1). Their rapid diagnosis is fundamental for patient survival and early hematopoietic stem cell transplantation. Here, we propose that studying γδ T cells, which are often neglected, can be helpful for a timely diagnosis. We thus offer a diagnostic flowchart and some lab tricks based on published cases.

CD3γ-independent pathways in TCR-mediated signaling in mature T and iNKT lymphocytes

Antigen recognition by T-lymphocytes through the T-cell antigen receptor, TCR-CD3, is a central event in the initiation of an immune response. CD3 proteins may have redundant as well as specific contributions to the intracellular propagation of TCR-mediated signals. However, to date, the relative role that each CD3 chain plays in signaling is controversial. In order to examine the roles of CD3γ chain in TCR signaling, we analyzed proximal and distal signaling events in human CD3γ(-/-) primary and Herpesvirus saimiri (HVS)-transformed T cells. Following TCR-CD3 engagement, certain early TCR signaling pathways (ZAP-70, ERK, p38 and mTORC2 phosphorylation, and actin polymerization) were comparable with control HVS-transformed T cells. However, other signaling pathways were affected, such TCRζ phosphorylation, indicating that the CD3γ chain contributes to improve TCR signaling efficiency and survival. On the other hand, CD3γ(-/-) primary invariant NKT cells (iNKT cells) showed a normal expansion in response to alpha-galactosylceramide (α-GalCer) and TCRVβ11(bright) iNKT cells were preferentially selected in this in vitro culture system, perhaps as a consequence of selective events in the thymus. Our results collectively indicate that a TCR lacking CD3γ can propagate a number of signals through the remaining invariant chains, likely the homologous CD3δ chain, which replaces it at the mutant TCR.

Primary T-cell immunodeficiency with functional revertant somatic mosaicism in CD247

To the Editor: T lymphocytes detect antigens with the T-cell receptor (TCR) composed of a variable heterodimer (either ab or gd), 2 invariant heterodimers (CD3gε and CD3dε), and an invariant homodimer (CD247 or zz). Because of the crucial role of TCR signaling in thymic selection, mutations in TCR, CD3, or CD247 selectively impair T-cell development, albeit to different degrees: deficiency of CD3d or CD3ε, but not of CD3g or CD247, causes severe T-cell lymphopenia. Their clinical outcome is also disparate, because CD3g deficiency does not require urgent transplantation. Thus, TCR immunodeficiencies display a range of phenotypes and careful differential diagnosis is essential for appropriate therapy. We describe an infant born to consanguineous parents with early-onset chronic cytomegalovirus infection, severe immunodeficiency, and extremely low surface TCR levels. Her immunologic characterization at age 11 months is summarized in Table E1 in this article’s Online Repository at www.jacionline.

Lymphocyte integration of complement cues

We address current data, views and puzzles on the emerging topic of regulation of lymphocytes by complement proteins or fragments. Such regulation is believed to take place through complement receptors (CR) and membrane complement regulators (CReg) involved in cell function or protection, respectively, including intracellular signalling. Original observations in B cells clearly support that complement cues through CR improve their performance. Other lymphocytes likely integrate complement-derived signals, as most lymphoid cells constitutively express or regulate CR and CReg upon activation. CR-induced signals, particularly by anaphylatoxins, clearly regulate lymphoid cell function. In contrast, data obtained by CReg crosslinking using antibodies are not always confirmed in human congenital deficiencies or knock-out mice, casting doubts on their physiological relevance. Unsurprisingly, human and mouse complement systems are not completely homologous, adding further complexity to our still fragmentary understanding of complement-lymphocyte interactions.

La enseñanza universitaria de Inmunología antes y después de Bolonia

Resumen Nos encontramos en un periodo de transicion hacia la construccion del Espacio Europeo de Educacion Superior (EEES), iniciado con la Declaracion de Bolonia de 1999 y regulado por el Real Decreto 55/2005. La ensenanza de la Inmunologia ya esta cambiando y aqui se pretende resumir el alcance de dichos cambios comparando antes y despues de Bolonia; lo que deberia ocurrir con lo que esta ocurriendo, y lo que podemos hacer al respecto desde nuestra area de responsabilidad.