IL-17–producing CD27 − γδ cells (γδ 27− cells) are widely viewed as innate immune cells that make critical contributions to host protection and autoimmunity. However, factors that promote them over IFN-γ–producing γδ 27+ cells are poorly elucidated. Moreover, although human IL-17–producing γδ cells are commonly implicated in inflammation, such cells themselves have proved difficult to isolate and characterize. Here, murine γδ 27− T cells and thymocytes are shown to be rapidly and substantially expanded by IL-7 in vitro and in vivo. This selectivity owes in substantial part to the capacity of IL-7 to activate STAT3 in such cells. Additionally, IL-7 promotes strong responses of IL-17–producing γδ cells to TCR agonists, thus reemphasizing the cells’ adaptive and innate potentials. Moreover, human IL-17–producing γδ cells are also substantially expanded by IL-7 plus TCR agonists. Hence, IL-7 has a conserved potential to preferentially regulate IL-17–producing γδ cells, with both biological and clinical implications.

Acknowledgement of the breadth of T-cell pleiotropy has provoked increasing interest in the degree to which functional responsiveness is elicited by environmental cues versus differentiation. This is particularly relevant for young animals requiring rapid responses to acute environmental exposure. In young mice, cd T cells are disproportionately important for immuno-protection. To examine the situation in humans, we compared populations and clones of T cells from term and preterm babies, and adults. By comparison with ab T cells, neonate-derived cd cells show stronger, pleiotropic functional responsiveness, and lack signatory deficits in IFN-c production. Emphasising the acquisition of functional competence in utero, IFN-c was produced by cd cells sampled from premature births, and, although one month's post-partum environmental exposure invariably increased their TNF-a production, it had no consistent effect on IFN-c or IL-2. In sum, cd cells seem well positioned at birth to contribute to immuno-protection and immuno-regulation, possibly compensating for selective immaturity in the ab compartment. With regard to the susceptibilities of preterm babies to viral infection, cd cells from preterm neonates were commonly impaired in Toll-like receptor-3 and -7 expression and compared with cells from term babies failed to optimise cytokine production in response to coincident TCR and TLR agonists. Key words: Neonate immunity . gd T cells . Toll-like receptors Supporting Information available online IntroductionAfter the protected intra-uterine environment, birth exposes the newborn mammal to precipitous encounter with antigens. Although several groups have concluded that lymphocytes from young animals can, under optimal conditions, successfully mount robust immune responses [1][2][3], it is also clear de facto that immune responses in children and young animals are sub-optimal and that neonates and infants are more vulnerable to infections, and respond less well to most vaccines than do older children or adults [4][5][6]. While different studies primarily attribute the problem to intrinsic defects in à These authors contributed equally to this work. 1794T cells or APC, respectively, it is likely that both are impaired in vivo [7].One particularly striking deficit reported in neonatal ab T cells is in IFN-g production, which underpins Th1 responses to intracellular parasites, bacteria and certain viruses. Such defects in conventional T-cell responses have fuelled the hypothesis that gd T cells, that are relatively rare in the blood and lymphoid circulation of adults, may contribute disproportionately to immune function in the young. Supporting this, weanling gd cell-deficient (TCR-d À/À ) mice, relative to wild-type counterparts, show a delayed acquisition of immune resistance to the natural gut pathogen, Eimeria vermiformis ([8] and our unpublished data). There is a similar susceptibility of young TCR-d À/À mice to infection by Cryptosporidium [9]. Provocatively, very early T-cell development is disproportionately di...

Background-Infection or stimulation of the innate immune system by nonspecific microbial antigens is thought to educate the immune system to respond appropriately to allergens, preventing allergy.

Although chronic intestinal helminth infections may suppress allergen-induced airway pathology by inducing a combination of modified T-helper (Th) 2 and immunosuppressive cytokines, a similar capacity of natural acute intestinal infections has remained untested, despite their global prevalence. Here, we show that allergic airway phenotypes including eosinophilia, eotaxin mRNA, and Th2 cytokines are significantly suppressed in animals that were infected by and that have cleared the intestinal parasite Eimeria vermiformis. Unlike in helminth-infected animals, regulation requires temporal coincidence of infection with sensitization; depends on interferon-gamma; and is not associated with an enhanced antigen-specific immunoglobulin G1 response. Moreover, regulation was effective following allergen sensitization in different anatomical sites, and in young and adult mice. These data highlight a transient anatomical dissemination of "functional immunologic dominance" following infection of the gut mucosa. They strongly support the hypothesis that airway allergies are naturally suppressed by both acute and chronic mucosal pathogens, but by different mechanisms.