Unbiased modifier screen reveals that signal strength determines the regulatory role murine TLR9 plays in autoantibody production.

The autoimmune disease systemic lupus erythematosus has a complex environmental and multifactorial genetic basis. Genome-wide association studies have recently identified numerous disease-associated polymorphisms, but it remains unclear in which cells and during which step of pathogenesis specific polymorphisms interact to cause disease. Using a mouse model in which the same activating mutation (CD45E613R) causes distinct genetic background-dependent disease phenotypes, we performed a screen for genetic modifiers of autoreactivity between anti-nuclear Ab (ANA)-resistant CD45E613R.B6 and ANA-permissive CD45E613R.BALB/c mice. Within a novel autoreactivity-associated locus on chromosome 9, we identify a putative modifier, TLR9. Validating a role for TLR9 in modifying autoreactivity in the context of the CD45E613R mutation, manipulation of TLR9 gene dosage eliminates ANA in CD45E613R.BALB/c mice, but confoundingly permits ANA in CD45E613R.B6 mice. We demonstrate that sensitivity to ANA is modulated by strength of TLR9 signal, because stronger TLR9(B6) signals, but not weaker TLR9(BALB/c) signals, negatively regulate CD45E613R B cell development during competitive reconstitution at the central tolerance checkpoint. Our results identify a novel autoreactivity-associated locus and validate Tlr9 as a candidate gene within the locus. We further demonstrate a novel role for TLR9 signal strength in central tolerance, providing insight into the interplay of disease-associated polymorphisms at a discrete step of systemic lupus erythematosus pathogenesis.

The junctional adhesion molecule JAML is a costimulatory receptor for epithelial gammadelta T cell activation.

Gammadelta T cells present in epithelial tissues provide a crucial first line of defense against environmental insults, including infection, trauma, and malignancy, yet the molecular events surrounding their activation remain poorly defined. Here we identify an epithelial gammadelta T cell-specific costimulatory molecule, junctional adhesion molecule-like protein (JAML). Binding of JAML to its ligand Coxsackie and adenovirus receptor (CAR) provides costimulation leading to cellular proliferation and cytokine and growth factor production. Inhibition of JAML costimulation leads to diminished gammadelta T cell activation and delayed wound closure akin to that seen in the absence of gammadelta T cells. Our results identify JAML as a crucial component of epithelial gammadelta T cell biology and have broader implications for CAR and JAML in tissue homeostasis and repair.

Gammadelta T cells are reduced and rendered unresponsive by hyperglycemia and chronic TNFalpha in mouse models of obesity and metabolic disease.

Epithelial cells provide an initial line of defense against damage and pathogens in barrier tissues such as the skin; however this balance is disrupted in obesity and metabolic disease. Skin gammadelta T cells recognize epithelial damage, and release cytokines and growth factors that facilitate wound repair. We report here that hyperglycemia results in impaired skin gammadelta T cell proliferation due to altered STAT5 signaling, ultimately resulting in half the number of gammadelta T cells populating the epidermis. Skin gammadelta T cells that overcome this hyperglycemic state are unresponsive to epithelial cell damage due to chronic inflammatory mediators, including TNFalpha. Cytokine and growth factor production at the site of tissue damage was partially restored by administering neutralizing TNFalpha antibodies in vivo. Thus, metabolic disease negatively impacts homeostasis and functionality of skin gammadelta T cells, rendering host defense mechanisms vulnerable to injury and infection.

T cell dependence on mTOR signaling.

The mammalian target of rapamycin (mTOR) signaling pathway integrates signals from the environment to the nucleus for the regulation of cellular growth, metabolism and survival. Lymphocytes frequently rely on this pathway, but it is carefully regulated through the reception of signals via cytokine, growth factor and co-stimulatory receptors. Recent studies have begun to elucidate why T cell subsets rely on this pathway to varying degrees. Ultimately these findings will help distinguish the parameters that guide T cell homeostasis and activation-induced function between the different T cell populations. The mTOR pathway has been the focus of many immunosuppressive and cancer treatment regimens, therefore there is a great need to understand the impact of suppression not only on the T cell populations targeted, but on bystander T cells as well.

Defects in skin gamma delta T cell function contribute to delayed wound repair in rapamycin-treated mice.

Disruptions in the normal program of tissue repair can result in poor wound healing, which perturbs the integrity of barrier tissues such as the skin. Such defects in wound repair occur in transplant recipients treated with the immunosuppressant drug rapamycin (sirolimus). Intraepithelial lymphocytes, such as gammadelta T cells in the skin, mediate tissue repair through the production of cytokines and growth factors. The capacity of skin-resident T cells to function during rapamycin treatment was analyzed in a mouse model of wound repair. Rapamycin treatment renders skin gammadelta T cells unable to proliferate, migrate, and produce normal levels of growth factors. The observed impairment of skin gammadelta T cell function is directly related to the inhibitory action of rapamycin on mammalian target of rapamycin. Skin gammadelta T cells treated with rapamycin are refractory to IL-2 stimulation and attempt to survive in the absence of cytokine and growth factor signaling by undergoing autophagy. Normal wound closure can be restored in rapamycin-treated mice by addition of the skin gammadelta T cell-produced factor, insulin-like growth factor-1. These studies not only reveal that mammalian target of rapamycin is a master regulator of gammadelta T cell function but also provide a novel mechanism for the increased susceptibility to nonhealing wounds that occurs during rapamycin administration.