CCR6 and NK1.1 distinguish between IL‐17A and IFN‐γ‐producing γδ effector T cells

γδ T cells are a potent source of innate IL‐17A and IFN‐γ, and they acquire the capacity to produce these cytokines within the thymus. However, the precise stages and required signals that guide this differentiation are unclear. Here we show that the CD24^low CD44^high effector γδ T cells of the adult thymus are segregated into two lineages by the mutually exclusive expression of CCR6 and NK1.1. Only CCR6⁺ γδ T cells produced IL‐17A, while NK1.1⁺ γδ T cells were efficient producers of IFN‐γ but not of IL‐17A. Their effector phenotype correlated with loss of CCR9 expression, particularly among the NK1.1⁺ γδ T cells. Accordingly, both γδ T‐cell subsets were rare in gut‐associated lymphoid tissues, but abundant in peripheral lymphoid tissues. There, they provided IL‐17A and IFN‐γ in response to TCR‐specific and TCR‐independent stimuli. IL‐12 and IL‐18 induced IFN‐γ and IL‐23 induced IL‐17A production by NK1.1⁺ or CCR6⁺ γδ T cells, respectively. Importantly, we show that CCR6⁺ γδ T cells are more responsive to TCR stimulation than their NK1.1⁺ counterparts. In conclusion, our findings support the hypothesis that CCR6⁺ IL‐17A‐producing γδ T cells derive from less TCR‐dependent selection events than IFN‐γ‐producing NK1.1⁺ γδ T cells.     

CD3 expression distinguishes two γδT cell receptor subsets with different phenotype and effector function in tuberculous pleurisy

Tuberculous pleurisy is a naturally occurring site of Mycobacterium tuberculosis (Mtb) infection. Herein, we describe the expression of activation, natural killer (NK) and cell migration markers, as well as effector functions from γδT cells in peripheral blood (PB) and pleural effusion (PE) from tuberculosis patients (TB). We observed a decreased percentage of circulating γδT from TB patients and differential expression of NK as well as of chemokine receptors on PB and PE. Two subsets of γδT cells were differentiated by the CD3/γδT cell receptor (γδTCR) complex. The γδTCR^low subset had a higher CD3 to TCR ratio and was enriched in Vδ2⁺ cells, whereas most Vδ1⁺ cells belonged to the γδTCR^high subset. In PB from TB, most γδTCR^high were CD45RA⁺CCR7^‐ and γδTCR^low were CD45RA^+/?CCR7⁺CXCR3⁺. In the pleural space the proportion of CD45RA^‐CCR7⁺CXCR3⁺ cells was higher. Neither spontaneous nor Mtb‐induced interferon (IFN)‐γ production was observed in PB‐γδT cells from TB; however, PE‐γδT cells showed a strong response. Both PB‐ and PE‐γδ T cells expressed surface CD107a upon stimulation with Mtb. Notably, PE‐γδTCR^low cells were the most potent effector cells. Thus, γδT cells from PB would acquire a further activated phenotype within the site of Mtb infection and exert full effector functions. As γδT cells produce IFN‐γ within the pleural space, they would be expected to play a beneficial role in tuberculous pleurisy by helping to maintain a T helper type 1 profile.     

CD45RA expression on γδ and αβ T cells emigrating from the fetal and postnatal thymus

We have compared the expression of CD45RA on αβ and γδ T cells emigrating from the fetal and postnatal thymus. The fetal and postnatal thymus export both CD45RA⁺ and CD45RA^- T cells. The number of γδ⁺CD45RA⁺ T cells was remarkably constant regardless of stage of ontogeny or T cell maturity. Around 5--8% of γδ thymic emigrants, thymocytes and peripheral blood lymphocytes expressed CD45RA in both fetal and postnatal animals. In contrast to γδ T cells, up to one quarter of both fetal and postnatal αβ emigrants expressed CD45RA. Post-thymic maturation of CD45RA expression on αβ emigrants, which occurred both before and after birth, appeared to be antigen independent.     

Preferentially expanding Vγ1+ γδ T cells are associated with protective immunity against Plasmodium infection in mice

γδ T cells play a crucial role in controlling malaria parasites. Dendritic cell (DC) activation via CD40 ligand (CD40L)‐CD40 signaling by γδ T cells induces protective immunity against the blood‐stage Plasmodium berghei XAT (PbXAT) parasites in mice. However, it is unknown which γδ T‐cell subset has an effector role and is required to control the Plasmodium infection. Here, using antibodies to deplete TCR Vγ1⁺ cells, we saw that Vγ1⁺ γδ T cells were important for the control of PbXAT infection. Splenic Vγ1⁺ γδ T cells preferentially expand and express CD40L, and both Vγ1⁺ and Vγ4⁺ γδ T cells produce IFN‐γ during infection. Although expression of CD40L on Vγ1⁺ γδ T cells is maintained during infection, the IFN‐γ positivity of Vγ1⁺ γδ T cells is reduced in late‐phase infection due to γδ T‐cell dysfunction. In Plasmodium‐infected IFN‐γ signaling‐deficient mice, DC activation is reduced, resulting in the suppression of γδ T‐cell dysfunction and the dampening of γδ T‐cell expansion in the late phase of infection. Our data suggest that Vγ1⁺ γδ T cells represent a major subset responding to PbXAT infection and that the Vγ1⁺ γδ T‐cell response is dependent on IFN‐γ‐activated DCs.     

γδ T cells come to stay: Innate skin memory in the Aldara model

The term immunological memory has long been a trademark restricted to adaptive lymphocytes such as memory B cells and plasma cells as well as memory CD8⁺ αβ T cells. In recent years, innate lymphocytes such as NK cells have also been shown to adapt to their environment by antigen‐specific expansion and selective survival. However, whether γδ T cells mount comparable memory responses to pathogenic stimuli is less well understood. In this issue of European Journal of Immunology, Hartwig et al. [Eur. J. Immunol. 2015. 45: 3022–3033] identify a subset of IL‐17‐producing γδ T cells that are capable of establishing long‐lived memory in the skin of mice exposed to imiquimod in the Aldara psoriasis model. These γδ T cells uniformly express a Vγ4⁺Vδ4⁺ TCR. They produce IL‐17A/F and persist in the dermis for long periods of time, also at untreated distal sites. Upon secondary challenge, experienced Vγ4⁺Vδ4⁺ cells show enhanced effector functions and mediate exacerbated secondary inflammation. These findings showcase innate γδ T‐cell memory that uses a single conserved public TCR combination. Furthermore, they provide mechanistic insight to the observed psoriatic relapses in patients in response to topical treatment with imiquimod.     

Activation of uterine intraepithelial γδ T cell receptor-positive lymphocytes during pregnancy

Intraepithelial lymphocytes (IEL) of the uterus of non-pregnant sheep were analyzed by single- and two-color flow cytometry. Very few lymphocytes carrying classical B and T cell markers (CD5, surface immunoglobulin) were detected in the uterine epithelial cell suspensions and all IEL expressed the CD8 surface marker although with varying intensities. Three distinct subpopulations were identified including a major (46-56%) population of CD8⁺CD45R^?γδ T cell receptor (TcR)-negative cells and approximately equal numbers of CD8⁺CD45R+γδTcR^? and CD8⁺CD45R⁺γδTcR⁺ lymphocytes. The same three subpopulations were also present in the interplacentomal areas of the uterus of ewes at a late stage of pregnancy but there was a dramatic increase (60-70%) in the γδ TcR⁺ subpopulation. In addition, a pronounced increase in both size and granularity was observed in the IEL population of pregnant uteri and this was attributed to the γδ TcR⁺ cells. Light and electron microscopic examination of these γδ TcR⁺ IEL revealed an increase in metabolic activity and the formation of exceptionally large cytoplasmic granules and confirmed their restricted localization within the uterine epithelium close to the trophoblast. These results represent for the first time, a clear example of the activation of γδ TcR⁺ cells which is not associated with an ongoing disease process or infection, γδ TcR⁺ cells have recently been observed in the epithelium of the murine reproductive tract and were characterized by their unique homogeneous receptor structure. The present results indicate that these cells may play an important physiological role during pregnancy.     

Increased Expression of Cell Surface Markers on Endometrial γδ T-Cell Receptor+ Intraepithelial Lymphocytes Induced by the Local Presence of the Sheep Conceptus

PROBLEM: In sheep, γδ T-cell receptor (TCR)⁺ cells are a major lymphocyte subpopulation in the luminal epithelium of the uterine endometrium. During late pregnancy, this population of T cells increases in number and becomes more granulated. This study was performed to determine whether this apparent activation was induced by local effects of the conceptus or systemic effects of pregnancy. METHODS: The unilaterally-pregnant ewe, in which the conceptus is surgically confined to one uterine horn, was used to distinguish between systemic and local effects of pregnancy on function of endometrial γδ TCR⁺ intraepithelial lymphocytes. Lymphocytes collected from peripheral blood, and from the endometrial luminal epithelium of cyclic and unilaterally-pregnant ewes (day 140 of gestation) were analyzed by flow cytometry. RESULTS: As compared to γδ TCR⁺ lymphocytes in peripheral blood, γδ TCR⁺ intraepithelial lymphocytes from non-pregnant ewes had a lower percentage of cells staining positive for CD25, CD44, and L-selectin. There was no effect of pregnancy on the percentage of γδ TCR⁺ peripheral blood lymphocytes staining positive for CD25, CD44, CD29, or L-selectin. Similarly, the percentage of intraepithelial lymphocytes staining positive for these antigens was similar for cells collected from cyclic ewes and cells from the nonpregnant uterine horn of unilaterally-pregnant ewes. In contrast, there was a higher percentage of CD25, CD44, CD29, and L-selectin⁺ cells for γδ TCR⁺ intraepithelial lymphocytes from the conceptus-containing uterine horn of pregnant ewes than for γδ TCR⁺ intraepithelial lymphocytes from the endometrium of cyclic ewes or from the nonpregnant uterine horn of pregnant ewes. CONCLUSION: The local presence of the conceptus causes changes in cell surface marker expression on endometrial γδ TCR⁺ intraepithelial lymphocytes during pregnancy. These changes may reflect conceptus-induced activation of this population of cells.     

mTOR signaling promotes a robust and continuous production of IFN‐γ by human memory CD8+ T cells and their proliferation

Human CD8⁺ T cells are functionally heterogeneous and can be divided into phenotypically and functionally distinct subsets according to CCR7 and CD45RA expression levels. Among these, CCR7^lowCD45RA^low effector memory CD8⁺ T cells (Tem) and CCR7^lowCD45RA^high CD8⁺ T cells, which are designated as Temra and considered to be terminally differentiated cells, are Ag‐experienced T cells but show different functionalities. Here, we show that, while Tem proliferate vigorously and produce IFN‐γ persistently and robustly, Temra proliferate poorly and lose the ability to produce IFN‐γ over time after TCR stimulation. Temra showed impaired cell growth upon TCR stimulation, which was associated with defective activation of the mammalian target of rapamycin (mTOR) signaling. Furthermore, rapamycin, an inhibitor of mTOR signaling, interfered with the robust and continuous proliferation of and IFN‐γ production by Tem at later time points after TCR stimulation. Thus, these data collectively indicate that activation of mTOR signaling is required for the robust functions of Tem cells in humans and suggest that defective mTOR signaling in Temra contributes to their functional impairment.     

Expansion of CD56+ NK T and γδ T cells from cord blood of human neonates

A particular T cell population expressing NK cell markers, CD56 and CD57, exists in humans. Many CD56⁺ T and CD57⁺ T cells (i.e. NK T cells) exist in the liver and increase in number in the blood with ageing. They may be a human counterpart of extrathymic T cells, similar to NK1.1⁺ CD3^int cells seen in mice. We investigate here the existence of such NK T cells in human cord blood and the in vitro expansion of these cells by the stimulation of human recombinant IL-2 (rIL-2). There were very small populations (< 1.0%) of CD56⁺ T cells, CD57⁺ T cells, and γδ T cells in cord blood. However, all of these populations increased in number after birth and with ageing. When lymphocytes in cord blood were cultured with rIL-2 (100 U/ml) for 14 days, CD56⁺ T cells expanded up to 25% of T cells. CD57⁺ T cells were never expanded by these in vitro cultures. The expansion of γδ T cells (mainly Vγ9^? non-adult type) also occurred in the in vitro culture. A considerable proportion of CD56⁺ T cells was found to use Vα24 (i.e. equivalent to invariant Vα14 chain used by murine NK T cells) for TCR αβ. These results suggest that neonatal blood contains only a few NK T cells but CD56⁺ NK T cells and γδ T cells are able to expand in vitro.     

Progenies of fetal thymocytes are the major source of CD4−CD8+ αα intestinal intraepithelial lymphocytes early in ontogeny

Present literature supports the view of an extrathymic origin for the subset of intestinal intraepithelial lymphocytes (IEL) that express the CD4^?CD8⁺ αα phenotype. This subset would include virtually all T cell receptor (TCR) γδ IEL and a portion of TCR αβ IEL. However, these reports do not exclude the possibility that some CD4^?CD8⁺ αα IEL are actually thymically derived. To clarify this issue, we examined the IEL day 3 neonatally thymectomized (NTX) mice. NTX resulted in as much as 80 % reduction in total TCR γδ IEL and in a nearly complete elimination of TCR αβ CD4^?CD8⁺ αα IEL early in ontogeny (3-to 5-week-old mice). The thymus dependency of TCR γδ IEL and TCR αβ CD4^?CD8⁺ IEL was less prominent in older mice (7- to 10-week-old mice), as the total number of these IEL increased in NTX mice, but still remained severalfold less than that in euthymic mice. Furthermore, we demonstrate, by grafting the fetal thymus of CBF1 (H-2^b/d) mice under the kidney capsule of congenitally nude athymic mice of BALB/c background (H-2^d), that a substantial number of TCR γδ IEL and TCR αβ CD4^?CD8⁺ αα IEL can be thymically derived (H-2^b+). In contrast, but consistent with our NTX data, grafting of adult thymi into nude mice generated virtually no TCR γδ IEL and relatively less TCR αβ CD4^?CD8⁺ αα IEL than did the grafting of fetal thymi. These results suggest that the thymus is the major source of TCR γδ and TCR αβ CD4^?CD8⁺ αα IEL early in ontogeny, but that the extrathymic pathway is probably the major source of these IEL later in ontogeny. A reassessment of the theory that most CD4^?CD8⁺ IEL are extrathymically derived is needed.     

Control of self-reactive cytotoxic T lymphocytes expressing γδ T cell receptors by natural killer inhibitory receptors

The majority of peripheral blood γδ T cells in human adults expresses T cell receptors (TCR) with identical V regions (Vγ9 and Vδ2). These Vγ9Vδ2 T cells recognize the major histocompatibility complex (MHC) class I-deficient B cell line Daudi and broadly distributed nonpeptidic antigens present in bacteria and parasites. Here we show that unlike αβ or Vγ9^? γδ T cells, the majority of Vγ9Vδ2T cells harbor natural killer inhibitory receptors (KIR) (mainly CD94/NKG2A heterodimers), which are known to deliver inhibitory signals upon interaction with MHC class I molecules. Within Vγ9δ2 T cells, KIR were mainly expressed by clones exhibiting a strong lytic activity against Daudi cells. In stark contrast, almost all Vγ9Vδ2 T cell clones devoid of killing activity were KIR^?, thus suggesting a coordinate acquisition of KIR and cytotoxic activity within Vγ9Vδ2 T cells. In functional terms, KIR inhibited lysis of MHC class I-positive tumor B cell lines by Vγ9Vδ2 cytotoxic T lymphocytes (CTL) and raised their threshold of activation by microbial antigens presented by MHC class I-positive cells. Furthermore, masking KIR or MHC class I molecules revealed a TCR-dependent recognition by Vγ9Vδ2 CTL of ligands expressed by activated T lymphocytes, including the effector cells themselves. Taken together, these results suggest a general implication of Vγ9Vδ2 T cells in immune response regulation and a central role of KIR in the control of self-reactive γδ CTL.     

Inhibition of murine γδ lymphocyte expansion and effector function by regulatory αβ T cells is cell‐contact‐dependent and sensitive to GITR modulation

γδ T cells are highly cytolytic lymphocytes that produce large amounts of pro‐inflammatory cytokines during immune responses to multiple pathogens. Furthermore, their ability to kill tumor cells has fueled the development of γδ‐T‐cell‐based cancer therapies. Thus, the regulation of γδ‐T‐cell activity is of great biological and clinical relevance. Here, we show that murine CD4⁺CD25⁺ αβ T cells, the vast majority of which express the Treg marker, Foxp3, abolish key effector functions of γδ T cells, namely the production of the pro‐inflammatory cytokines, IFN‐γ and IL‐17, cytotoxicity, and lymphocyte proliferation in vitro and in vivo. We further show that suppression is dependent on cellular contact between Treg and γδ T cells, results in the induction of an anergic state in γδ lymphocytes, and can be partially reversed by manipulating glucocorticoid‐induced TNF receptor‐related protein (GITR) signals. Our data collectively dissect a novel mechanism by which the expansion and pro‐inflammatory functions of γδ T cells are regulated.     

Characteristics of fetal thymus-derived T cell receptor γδ intestinal intraepithelial lymphocytes

We have previously demonstrated that grafting of CBF1(H-2^b/d) fetal thymus (FTG) under the kidney capsule of congenitally athymic nude mice of BALB/c background (H-2^d) generates a substantial number of T cell receptor (TCR) γδ intestinal intraepithelial lymphocytes (IEL) that were of FTG origin (H-2^b+) (see accompanying report). Here we investigated the characteristics of these FTG-derived TCR γδ IEL and compared them to the extrathymically derived TCR γδ IEL found in nude mice. Phenotypically, FTG-derived TCR γδ IEL were similar to their extrathymically derived counterparts in that most were Thy-1 ^?, CD5^? and CD8αα (homodimer). Vγ and Vδ gene usage in thymus-derived and extrathymically derived TCR γδ IEL were found to be virtually the same. Functionally, FTG-derived TCR γδ IEL were similar to the TCR γδ IEL found in euthymic mice as both were relatively anergic to TCR cross-linking in vitro. However, FTG-derived TCR γδ IEL differed slightly from extrathymically derived TCR γδ IEL, which were completely nonresponsive to the same in vitro stimulation. Overall, these findings support the view that FTG-derived and extrathymically derived TCR γδ IEL are almost indistinguishable. Lastly, we demonstrate that despite their thymic origin, development of FTG-derived TCR γδ IEL partially takes place extrathymically; that is positive selection of FTG-derived Vδ4 IEL occurs extrathymically. In addition, we demonstrate that the CD8 molecule is not necessary for development and homing of FTG-derived TCR γδ IEL. This later finding suggests that the CD8αα molecule develops extrathymically for FTG-derived CD8αα TCR γδ IEL.     

Normal macrophage functions,but impaired induction of γδ T cells,at the site of bacterial infection in CD45 exon 6-deficient mice

We investigated the protective functions of macrophages and γδ T cells in adult CD45 exon 6-deficient (CD45?/?) mice against an intraperitoneal (i.p.) infection with Listeria monocytogenes. γδ T cells are preferentially localized in the spleen, liver, and intraperitoneal cavity of the adult CD45?/? mice. Increased numbers of γδ T cells were observed after i.p. infection with L. monocytogenes in the peritoneal cavity of C57BL/6 (CD45+/+) mice but not in CD45?/? mice. The γδ T cells showed predominant usage of Vδ5 and Vδ6 rearranged to Jδ1 in the infected CD45?/? mice which are the same as those used by resident γδ T cells of noninfected CD45+/+ and CD45?/? mice. Furthermore, we analyzed the protective abilities of the CD45?/?, CD45+/+, and γδ T cell-depleted mice at the early stage of the listerial infection. The numbers of bacteria in the spleens and livers of the CD45?/? mice 5 days after the listerial infection were almost ten times larger than those in the CD45?/? and γδ T cell-depleted CD45+/+ mice. Macrophages showed normal antigen presentation, nitric oxide production and bactericidal activity for L. monocytogenes despite their lacking CD45 surface expression, suggesting that CD45-negative macrophages have a minimal influence on the increased bacterial multiplication in the CD45?/? mice. These results suggest that the γδ T cells are induced by the bacterial infection in a CD45-dependent manner, and that unresponsiveness of the γδ T cells results in only weak protection against L. monocytogenes in CD45?/? mice.     

Helper activity of CD4+ αβ T cells is required for the avian γδ T cell response

We have studied the in vitro activation of chicken γδ T cells. Both splenic αβ and γδ T cells obtained from complete Freund's adjuvant-primed chickens proliferated in vitro when stimulated with mycobacterial sonicate or purified protein derivative of Mycobacterium tuberculosis. When CD4⁺ cells or αβ T cell receptor (TcR)-positive cells were removed, both the proliferation and the blast formation of γδ T cells in response to mycobacterial antigens were abrogated. The response was restored if supernatant from concanavalin A (Con A)-activated lymphocyte cultures (CAS) as a source of helper factors was added together with the specific antigen purified protein derivative. The CD4- or αβ TcR-depleted cells still proliferated in response to Con A, although a decrease of the response was observed. To analyze the γδ T cell response more specifically we stimulated peripheral blood cells with immobilized monoclonal antibodies against T cell receptor. Anti-γδ TcR antibody alone did not induce significant proliferation. When CAS was added together with the anti-γδ TcR monoclonal antibody, a strong proliferation of γδ T cells was observed. In contrast, both Vβ1- and Vβ2-expressing αβ T cells proliferated in vitro in response to stimulation with the relevant anti-TcR monoclonal antibody alone. Depletion of either Vβ1⁺ or Vβ2⁺ T cell subset alone had no negative effect on the proliferation or blast formation of γδ T cells stimulated with mycobacterial antigens. Taken together our results suggest that CD4⁺ αβ T cells (both Vβl- and Vβ2-expressing) play a role in the activation and response of chicken γδ T cells.     

The surface epithelium of recurrent infected palatine tonsils is rich in γδ T cells

Using a large panel of MoAbs in quantitative morphometric analysis of immunohistochemically stained tissue sections, we compared the frequency and distribution of immune cells in palatine tonsils from patients with recurrent tonsillitis (RT) and patients with idiopathic tonsillar hypertrophy (ITH). We found that differences between the two patient groups in leucocyte populations were limited to the surface epithelium, whereas the cellular composition of interfollicular and follicular areas was similar. Most intraepithelial lymphocytes were CD8⁺ T cells in both groups. However, the number of intraepithelial T cells was significantly higher in RT compared with ITH. This was due to a selective increase in the number of intraepithelial CD8⁺γδ T cells utilizing Vδ1 and Vγ9. In both patient groups the majority of the intraepithelial γδ T cells expressed Vδ1 and Vγ9. Subepithelially, γδ T cells utilizing Vγ9 dominated over cells utilizing Vγ8, while equal proportions expressed Vδ1 and Vδ2. These results suggest that cells utilizing the otherwise rare combination Vδ1/Vγ9 in their T cell receptors (TCR) may constitute a major γδ T cell population in palatine tonsils and are probably reactive to antigens specific to the tonsillar milieu. Furthermore, they indicate that preferentially this γδ T cell subpopulation is involved in immune reactions within the surface epithelium in RT. We speculate that γδ T cells are involved in clearing infectious bacteria at the tonsillar surface and in limiting inflammatory responses in the tonsils. Both local expansion and infiltration of blood cells probably contribute to the high numbers of γδ T cells in RT patients.     

Cytomegalovirus drives Vδ2neg γδ T cell inflation in many healthy virus carriers with increasing age

Cytomegalovirus (CMV) usually causes lifelong asymptomatic infection, but over time can distort immune profiles. Recent reports describe selective expansion of Vδ2^neg γδ T cells in healthy and immunocompromised CMV carriers. Having shown previously that virus‐specific CD8⁺ and CD4⁺ T cell responses are increased significantly in elderly CMV carriers, probably driven by chronic stimulation, we hypothesized that Vδ2^neg γδ T cells may also be expanded with age. Our results show that Vδ2^neg γδ T cells are increased significantly in CMV‐seropositive healthy individuals compared to CMV‐seronegative controls in all age groups. The differences were most significant in older age groups (P < 0·0001). Furthermore, while Vδ2^neg γδ T‐ cells comprise both naive and memory cells in CMV‐seronegative donors, highly differentiated effector memory cells are the dominant phenotype in CMV carriers, with naive cells reduced significantly in numbers in CMV‐seropositive elderly. Although phenotypically resembling conventional CMV‐specific T cells, Vδ2^neg γδ T cells do not correlate with changes in magnitude of CMV‐specific CD4⁺ or CD8⁺ T cell frequencies within those individuals, and do not possess ex‐vivo immediate effector function as shown by CMV‐specific CD4⁺ and CD8⁺ T cells. However, after short‐term culture, Vδ2^neg γδ T cells demonstrate effector T cell functions, suggesting additional requirements for activation. In summary, Vδ2^neg γδ T cells are expanded in many older CMV carriers, demonstrating a further level of lymphocyte subset skewing by CMV in healthy individuals. As others have reported shared reactivity of Vδ2^neg γδ T cells towards tumour cells, the composition of γδ T cell subsets may also have implications for risk of developing cancer in elderly people.     

Lymphocytes bearing the γδ T cell receptor in acute Brucella melitensis infection

A phenotypical analysis carried out by indirect immunofluorescence and two-color cytofluorometry showed that the number of lymphocytes bearing the γδ T cell receptor (TcR) heterodimer was dramatically increased in the blood of six children with Brucella melitensis infection. Most in vivo expanded γδ T cells reacted with a monoclonal antibody which identifies Vδ2 gene products and a significant proportion expressed CD25 and HLA-DR activation antigens. In addition, whereas only a few γδ T lymphocytes were CD8⁺, nearly all were CD4^?. Highly enriched populations of both αβ and γδ T cells were obtained by negative immunoselection from three subjects with brucellosis sampled during convalescence. Despite the different form of their TcR, the proliferation of these two major T cell subsets in response to a mitogenic anti-CD3 monoclonal reagent (OKT3) was optimal. In contrast, αβ, but not γδ, T lymphocytes proliferated vigorously in response to the antigenic stimulus elicited by heat-killed Brucella. Further studies are, therefore, needed to determine whether the selective expansion of the γδ T cell subpopulation observed during the clinical course of the infection is driven by antigenic determinant(s) borne by the pathogen in vivo or is due to host-derived stimuli, such as autologous heat-shock proteins expressed on the surface of the infected cells.