Decreased peripheral blood γδ T cells in patients with bronchial asthma

Many cell populations are thought to be involved in the etiopathogenesis of bronchial asthma. We examined by flow cytometry the relative and absolute number of CD3*, CD4*, CD8*γδ TcR* T cells. CD19* B cells; and CD56* natural killer (NK) cells in the peripheral blood of 26 adult patients with difficult-to-control asthma (DCA) and 22 patients with minimally symptomatic asthma (MSA). Statistically higher relative and absolute numbers of NK cells (18.39±10.67% and 0.38±0.17×10⁹/l) in comparison with healthy controls (ll.77±8.06% and 0.25±0.19×10⁹/l) and significantly decreased relative and absolute numbers of γδ T cells (3.02±2.16% and 0.06±0.04×10⁹/l) in comparison with controls (5.65+2.90% and 0.13±0.08×10⁹/l) in the DCA patient group were found. After pooling of data from both MSA and DCA patients and dividing the patients according to the presence of allergy, the relative and absolute numbers of 78 T celts were found to be diminished in both the allergy (3.77±2.98 and O.O7±0.O5 ×10⁹/l) and nonallergy (3.06±1.78% and 0.06±0.03 ×10⁹/l) groups in comparison with healthy controls. The reason for the low number of 78 T cells in the peripheral blood of patients suffering from bronchial asthma is under investigation.     

Vδ1+ Gamma/Delta T Lymphocytes Infiltrating Human Lung Cancer Express the CD8α/α Homodimer

Murine γ/δ T lymphocytes localize to different epithelial tissues and are phenotypically distinct from peripheral γ/δ T cell-populations in that they show limited TCR diversity, express the CD8 α/α homodimer and lack the CD8β chain. In humans, a compartmentalization of γ/δ cells sharing similar phenotypic features has been documented to date only in the case of intestinal epithelium. In the present study we show that about half of Vδ1⁺ (as well as Vδ1⁻Vδ2⁻) γ/δ lymphocytes, which can be selectively expanded from human lung cancers, coexpress the CD8α/α homodimer. The accumulation of intraepithelial CD8⁺γ/δ⁺ lymphocytes might then be a more general phenomenon, possibly as a result of common mechanisms operating at those sites.     

Crucial function of the pre-T-cell receptor (TCR) in TCRP selection, TCRβ allelic exclusion and αβ versus γδ lineage commitment

Summary: The analysis of T-cell receptor (TCR) βselection, TCRβ allelic exclusion and TCRβ rearrangement in γδ T cells from normal and pre-TCR-deficient mice has shown that the pre-TCR has a crucial role in T-lyinpbocyte development:

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  The pre-TCR is by far the most effective receptor that generates large numbers of CD4⁺8⁺ T cells with productive TCRβ rearrangements.
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  In the absence of the pre-TCR, TCRβ rearrangement proceeds in developing cells irrespective of whether they already contain a productive TCRβ gene.
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  The pre-TCR directs developing T cells to the αβ lineage because y5 T cells from pTα^-/- mice proceed much further in TCRβ rearrangement than γδ T cells from wild-type mice. It is argued that the pre-TCR commits developing T cells to the αβ lineage by an instructive mechanism, which has largely replaced an evolutionarily more ancient mechanism that involves stochastic αβ lineage commitment.

     

γδ T-cell receptors: functional correlations

Summary:  The γδ T-cell receptors (TCRs) are limited in their diversity, suggesting that their natural ligands may be few in number. Ligands for γδTCRs that have thus far been determined are predominantly of host rather than foreign origin. Correlations have been noted between the Vγ and/or Vδ genes a γδ T cell expresses and its functional role. The reason for these correlations is not yet known, but several different mechanisms are conceivable. One possibility is that interactions between particular TCR-V domains and ligands determine function or functional development. However, a recent study showed that at least for one ligand, receptor specificity is determined by the complementarity-determining region 3 (CDR3) component of the TCR-δ chain, regardless of the Vγ and/or Vδ. To determine what is required in the TCR for other specificities and to test whether recognition of certain ligands is connected to cell function, more γδTCR ligands must be defined. The use of recombinant soluble versions of γδTCRs appears to be a promising approach to finding new ligands, and recent results using this method are reviewed.     

Skin γδ T-cell functions in homeostasis and wound healing

Summary:  There is a resident population of T cells found in murine skin that expresses an invariant Vγ3Vδ1 T-cell receptor (TCR), and these cells are significantly different from lymphoid γδ T cells and αβ T cells in terms of ontogeny, tissue tropism, and antigen receptor diversity. These dendritic epidermal T cells are derived from fetal thymic precursor cells, are in constant contact with neighboring epidermal cells, and express a monoclonal γδTCR only found in the skin. Skin γδ T cells have been shown to play unique roles in tissue homeostasis and during tissue repair through local secretion of distinct growth factors including keratinocyte growth factors and insulin-like growth factor-1. In this review, we discuss evidence supporting a role for cross talk between skin γδ T cells and keratinocytes that contributes to the maintenance of normal skin and wound healing.     

Antigen recognition by γδ T cells

Summary:  γδ T cells contribute to host immune competence uniquely. This is most likely because they have distinctive antigen-recognition properties. While the basic organization of γδ T-cell receptor (TCR) loci is similar to that of αβ TCR loci, there is a striking difference in how the diversity of γδ TCRs is generated. γδ and αβ T cells have different antigen-recognition requirements and almost certainly recognize a different set of antigens. While it is unclear what most γδ T cells recognize, the non-classical major histocompatibility complex class I molecules T10 and T22 were found to be the natural ligands for a sizable population (0.2–2%) of murine γδ T cells. The recognition of T10/T22 may be a way by which γδ T cells regulate cells of the immune system, and this system has been used to determine the antigen-recognition determinants of γδ T cells. T10/T22-specific γδ T cells have TCRs that are diverse in both V gene usage and CDR3 sequences. Their Vγ usage reflects their tissue origin, and their antigen specificity is conferred by a motif in the TCR δ chain that is encoded by V and D segments and by P-nucleotide addition. Sequence variations around this motif modulate affinities between TCRs and T10/T22. That this CDR3 motif is important in antigen recognition is confirmed by the crystal structure of a γδ TCR bound to its ligand. The significance of these observations is discussed in the context of γδ T-cell biology.     

γδ T-Cell Precursor-Derived CD4− CD8−αβ T Cells Retain γδ Cell Function

We have previously shown that some of the DNαβ⁺ T cells arising in TcRα-chain transgenic mice are of γδ T cell origin, based on phenotypic data and on their status of TcR gene rearrangements. In the present report we investigated the impact of αβ TcR expression on the functional programme of the mature γδ precursor-derived DNαβ⁺ T cells. Our results demonstrate that both their proliferative capacity and their cytokine production profile are similar to that of γδ T cells. Furthermore, both transgenic DNαβ⁺ T cells and DNγδ⁺ T cells up-regulate CD8α expression after activation, but, in contrast to CD4⁺αβ T cells, are unable to induce proliferation of naive B cells. Thus, our results suggest that the effector functions of mature T cells are determined independently of the TcR isotype, probably at an early stage of differentiation, and thereby have important implications for current models of T-cell lineage commitment.     

Development and selection of γδ T cells

Summary:  Two main lineages of T cells develop in the thymus: those that express the αβ T-cell receptor (TCR) and those that express the γδ TCR. Whereas the development, selection, and peripheral localization of newly differentiated αβ T cells are understood in some detail, these processes are less well characterized in γδ T cells. This review describes research carried out in this laboratory and others, which addresses several key aspects of γδ T-cell development, including the decision of precursor cells to differentiate into the γδ versus αβ lineage, the ordered differentiation over the course of ontogeny of functional γδ T-cell subsets expressing distinct TCR structures, programming of ordered Vγ gene rearrangement in the thymus, including a molecular switch that ensures appropriate Vγ rearrangements at the appropriate stage of development, positive selection in the thymus of γδ T cells destined for the epidermis, and the acquisition by developing γδ T cells of cues that determine their correct localization in the periphery. This research suggests a coordination of molecularly programmed events and cellular selection, which enables specialization of the thymus for production of distinct T-cell subsets at different stages of development.     

γδ intraepithelial lymphocytes drive tumor necrosis factor-α responsiveness to intestinal iron challenge: relevance to hemochromatosis

Summary: The dependence of intestinal epithelial cell (IEC) growth and differentiation on intraepithelial lymphocytes (IELs) expressing the gamma/delta (γδ) T-cell receptor (TCR), suggested a potential role for γδ⁺ IELs in the regulation of iron absorption. We therefore examined the levels of hepatic iron and the IEL cytokine responses in C57BL/6J control and class I and TCR knockout lines (placed on a C57BL/6J genetic background) following the administration of supplemental dietary iron. The highest level of liver iron was found in the β2-microglobulin knockout (β2m^-/-) mice followed by the TCR-δ knockout (TCRδ^-/-) animals. TCR-α knockout (TCRα^-/-) and control animals did not differ in their iron levels. Liver iron loading correlated inversely with rhe ability of the mice to generate an IEL tumor necrosis factor (TNE)-α response. These observations suggest a model in which IEC iron loading is communicated to IELs via the HFE class I protein. The result of this communication is the initiation of TNE-α release by γδ⁺ IELs (sustained by macrophages and dendritic cells) contributing to the upregulation of ferritin expression and possibly to the normal maintenance of the IEC apoptotic pathway.     

Nonpeptide antigens, presentation mechanisms, and immunological memory of human Vγ2Vδ2 T cells: discriminating friend from foe through the recognition of prenyl pyrophosphate antigens

Summary:  Human Vγ2Vδ2 T cells play important roles in mediating immunity against microbial pathogens and have potent anti-tumor activity. Vγ2Vδ2 T cells recognize the pyrophosphorylated isoprenoid intermediates ( E )-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), an intermediate in the foreign 2- C -methyl- d -erythritol 4-phosphate (MEP) pathway, and isopentenyl pyrophosphate (IPP), an intermediate in the self-mevalonate pathway. Infection with bacteria and protozoa using the MEP pathway leads to the rapid expansion of Vγ2Vδ2 T cells to very high numbers through preferential recognition of HMBPP. Activated Vγ2Vδ2 T cells produce proinflammatory cytokines and chemokines, kill infected cells, secrete growth factors for epithelial cells, and present antigens to αβ T cells. Vγ2Vδ2 T cells can also recognize high levels of IPP in certain tumors and in cells treated with pharmacological agents, such as bisphosphonates and alkylamines, that block farnesyl pyrophosphate synthase. Activated Vγ2Vδ2 T cells are able to kill most tumor cells because of recognition by T-cell receptor and natural killer receptors. The ubiquitous nature of the antigens converts essentially all Vγ2Vδ2 T cells to memory cells at an early age. Thus, primary infections with HMBPP-producing bacteria are perceived by Vγ2Vδ2 T cells as a repeat infection. Extensive efforts are underway to harness these cells to treat a variety of cancers and to provide microbial immunity.     

Preferential Vδ1 Expression among TcR γ/δ -Bearing T Cells in Human Oral Epithelium

The oral cavity is a septic area colonized by various bacterial species, and the oral mucosa is frequently submitted to microtraumas. Several mechanisms are implicated in the defence of the oral tissue, but little is known concerning the eventual presence and role of γ/δ T cells at this site.
Samples of healthy keratinized oral mucosa were examined with immunochemica! techniques using anti-CD3, CD4, CD8, CD22, TcRδ1, Vδl and Vδ2 monoclonal antibodies. Whatever the site examined. γ/δ T cells represent at most 2% of the T-cell population, a value similar to that found in other tissues. In the connective tissue, under the basement membrane, Vδ2⁺γ/δ T cells are predominant whereas the epithelium mostly contains Vδ⁺γ/δ T cells. The significance of this preferential Vδ1 intraepithelial presence is discussed.     

Different Percentages of Peripheral Blood γδ+ T Cells in Healthy Individuals from Different Areas of the World

The frequency of γδ⁺ T cells in the peripheral blood of 26 Turkish, 24 Swedish, 35 Japanese and 14 'Asian' (non-Japanese) healthy blood donors and healthy volunteers were investigated by flow cytometry. In the Turkish group, 9.3% (median value) of the CD3⁺ peripheral blood T cells expressed the γδ T cell receptor. A similar level of γδ⁺ T cells was found in the non-Japanese 'Asian' healthy volunteers (9.2%), while significantly lower values were detected in the Swedish (4.2%) and Japanese (4.5%) groups. These dramatic differences in normally occurring γδ⁺ T cells in different groups of healthy individuals were further reflected by a low incidence of >10% γδ⁺ T cells in the Swedish (0/24) and Japanese (6/35) groups compared to the Turkish (12/26) and 'Asian' (5/14) groups. The described γδ⁺ T cell differences between distinct ethnic groups are thus likely to be a consequence of environmental factors, but additional genetic influences cannot be ruled out. The present study demonstrates the potential importance of the ethnic origin and environmental history of subjects examined in studies of γδ⁺ T cells–disease relations.     

Acute, Lethal Graft-Versus-Host Disease in an F1-Hybrid Model using Grafts from Parental-Strain, T-Cell Receptor-δ Gene Knockout Donors

γδT cells have been implicated in the pathogenesis of acute graft-versus-host disease (GVHD). We therefore performed experiments to determine whether mortality from GVHD is reduced in C57BL/6 × DBA/2 F₁-hybrid (BDF₁-hybrid) mice when parental strain, T-cell receptor-δ (TCRδ) knockout (KO) donors are used. We compared mortality, weight loss, interferon-γ (IFN-γ) production and cytotoxic activity in recipients of either wild-type or TCRδ KO grafts. In both groups there was significant weight loss and an identical level of mortality. Elevated IFN-γ levels were present in both groups, but recipients of TCRδ KO grafts produced twice as much as recipients of wild-type grafts. Elevated natural killer (NK) and NK-like activity was also seen in both. These results demonstrate that TCRδ KO grafts can induce GVHD as severe as that seen in recipients of wild-type grafts, a finding that is at odds with studies demonstrating reduced mortality when γδT cells are purged from donor mice. We suggest that the inconsistency may lie in the higher levels of IFN-γ seen with TCRδ KO grafts and that the protection afforded by the absence of γδT cells in the graft is overwhelmed by the higher levels of IFN-γ.     

Oestrogen Treatment Depletes Extrathymic T Cells from Intestinal Lymphoid Tissues

Different lineages of thymic and extrathymic T cells are found in the epithelial layer and in the lamina propria of the small and large intestine of euthymic and athymic mice. A single subcutaneous injection of oestradiolvalorat (Progynon^®-Depot-10, Schering, Berlin, Germany) into athymic mice led to a dose-dependent depletion of extrathymic T cells from the intraepithelial and lamina propria compartments of the small and large intestine. TCRαβ and TCRγδ, CD4⁺ and CD8α⁺ T cell subsets were affected. The depletion of intraepithelial, extrathymic T cells by oestradiol treatment was striking. Oestrogen, therefore, has an effect not only on genital mucous membranes, but also on the large, diffuse lymphoid tissues of the gut, in that it selectively depletes the intestinal, extrathymic T-cell subsets.     

Regulatory T cells in spontaneous autoimmune encephalomyelitis

Summary: Spontaneous experimental autoimmune encephalomyelitis (EAE) develops in 100% of mice harboring a monoclonal myelin basic protein (MBP)-specific CD4⁺αβ T-cell repertoire. Monoclonality of the αβ T-cell repertoire can be achieved by crossing MBP-specific T-cell receptor (TCR) transgenic mice with either RAG^−/− mice or TCR α^−/−/TCR β^−/− double knockout mice. Spontaneous EAE can be prevented by a single administration of purified CD4⁺ splenocytes or thymocytes obtained from wild-type syngeneic mice. The regulatory T cells (T-reg) that protect from spontaneous EAE need not express the CD25 marker, as effective protection can be attained with populations depleted of CD25⁺ T cells. Although the specificity of the regulatory T cells is important for their generation or regulatory function, T cells that protect from spontaneous EAE can have a diverse TCR α and β chain composition. T-reg cells expand poorly in vivo , and appear to be long lived. Finally, precursors for T-reg are present in fetal liver as well as in the bone marrow of aging mice. We propose that protection of healthy individuals from autoimmune diseases involves several layers of regulation, which consist of CD4⁺CD25⁺ regulatory T cells, CD4⁺CD25⁻ T-reg cells, and anti-TCR T cells, with each layer potentially operating at different stages of T-helper cell-mediated immune responses.     

Ca2+ permeability of the channel pore is not essential for the δ2 glutamate receptor to regulate synaptic plasticity and motor coordination

The δ2 glutamate receptor (GluRδ2) plays a crucial role in cerebellar functions; mice with a disrupted GluR δ 2 gene ( GluR δ 2^−/− ) display impaired synapse formation and abrogated long-term depression (LTD). However, the mechanisms by which GluRδ2 functions have remained unclear. Because a GluRδ2 mutation in lurcher mice causes channel activities characterized by Ca²⁺ permeability, GluRδ2 was previously suggested to serve as a Ca²⁺-permeable channel in Purkinje cells. To test this hypothesis, we introduced a GluR δ 2 transgene, which had a mutation (Gln618Arg) in the putative channel pore, into GluR δ 2^−/− mice. Interestingly, the mutant transgene rescued the major functional and morphological abnormalities of GluR δ 2^−/− Purkinje cells, such as enhanced paired-pulse facilitation, impaired LTD at parallel fibre synapses, and sustained innervation by multiple climbing fibres. These results indicate that the conserved glutamine residue in the channel pore, which is crucial for all Ca²⁺-permeable glutamate receptors, is not essential for the function of GluRδ2.     

Thymic differentiation of TCRαβ+ CD8αα+ IELs

Summary:  Intraepithelial lymphocytes (IELs) contain several subsets, but the origin of the T-cell receptor (TCR)αβ⁺ CD8αα⁺ IELs has been particularly controversial. Here we provide a synthesis, based on recent work, that attempts to unify the divergent views. The intestine has a primordial function in lymphopoiesis, and precursors with the potential to differentiate into T cells are found both in the epithelium and underlying lamina propria. Moreover, the thymus has been reported to export cells to the intestine that are not fully differentiated. TCRαβ⁺ CD8αα⁺ IELs can differentiate in the intestine from each of these sources, but in normal euthymic mice, the thymus appears to be the major source for TCRαβ⁺ CD8αα⁺ IELs. This unique IEL subset is a self-reactive population that requires exposure to self-agonists for selection in the thymus, similar to other regulatory T-cell populations. IELs transition through a double-positive (DP) intermediate in the thymus, but they originate from a subset of the DP cells that can be identified by its expression of CD8αα homodimers. The agonist-selected cells in the thymus are TCRβ⁺ but CD4 and CD8 double negative. The evidence suggests that reacquired expression of CD8αα and downregulation of CD5 occur after thymus export, perhaps in the intestine under the influence of interleukin-15. As a result of agonist exposure, a new gene expression program is activated. Therefore, the increased understanding of the developmental origin of TCRαβ⁺ CD8αα⁺ IELs may help us to understand how they participate in immune regulation and protection in the intestine.     

A retrospective on the requirements for γδ T-cell development

Summary:  Since the discovery of γδ T cells two decades ago, considerable effort has been made to understand their developmental program, their antigen specificity, and their contribution to the immune response. In this review, we focus on what is known about γδ T-cell development and on the advances that have been made in determining which genes are required. In addition, we compare the genetic requirements for αβ and γδ T-cell development with the hope of gaining a better picture of the signaling pathways that govern the development of γδ lineage cells.