Intravital visualization of autoimmune-induced tissue damage and Treg cell protection shows contact-based immune cell interactions and growth of bystander tissue cells in pancreatic islet grafts.

While memory CD4 T cells are critical for effective immunity to pathogens, the mechanisms underlying their generation are still poorly defined. We find that following murine influenza infection, most effector CD4 T cells undergo apoptosis unless they encounter cognate Ag at a defined stage near the peak of effector generation. Ag recognition at this “memory checkpoint” blocks default apoptosis and programs their transition to long-lived memory. Strikingly, we find that viral infection is not required, as memory formation can be restored by the addition of short-lived, Ag-pulsed APC at this checkpoint. The resulting memory CD4 T cells express an enhanced memory phenotype, have increased cytokine production, and provide protection against lethal influenza infection. Finally, we find that memory CD4 T cell formation following cold-adapted influenza vaccination is boosted when Ag is administered during this checkpoint. These findings imply that persistence of viral Ag presentation into the effector phase is the key factor that determines the efficiency of memory generation. We also suggest that administering Ag at this checkpoint may improve vaccine efficacy.

CD4 T cells can differentiate into multiple effector subsets, including ThCTL that mediate MHC-II restricted cytotoxicity. Although CD4 T cell mediated cytotoxicity has been reported in multiple viral infections, their characteristics and the factors regulating their generation are unclear, in part due to a lack of a signature marker. We show here that in mice, NKG2C/E identifies the ThCTL that develop in the lung during influenza A virus (IAV) infection. ThCTL express the NKG2X/CD94 complex, in particular the NKG2C/E isoforms. NKG2C/E+ ThCTL are part of the lung CD4 effector population and they mediate IAV-specific cytotoxic activity. The phenotype of NKG2C/E+ ThCTL indicates they are highly activated effectors expressing high levels of binding to P-selectin, T-bet and Blimp-1, and that more of them secrete IFNγ and readily degranulate than non-ThCTL. ThCTL also express more cytotoxicity-associated genes including perforin and granzymes and fewer genes associated with recirculation and memory. They are found only at the site of infection and not in other peripheral sites. These data suggest ThCTL are marked by the expression of NKG2C/E and represent a unique CD4 effector population specialized for cytotoxicity.

The rough coat (rc) spontaneous mutation causes sebaceous gland hypertrophy, hair loss and extracutaneous abnormalities including growth retardation. The rc mice have a missense mutation in the predicted immunoglobulin protein Mpzl3. In this study, we generated Mpzl3 knockout mice to determine its functions in the skin. Homozygous Mpzl3 knockout mice showed unkempt and greasy hair coat and hair loss soon after birth. Histological analysis revealed severe sebaceous gland hypertrophy and increased dermal thickness, but did not detect significant changes in the hair cycle. Mpzl3 null mice frequently developed inflammatory skin lesions; however, the early onset skin abnormalities were not the results of immune defects. The abnormalities in the Mpzl3 knockout mice resemble closely those observed in the rc/rc mice, as well as mice heterozygous for both the rc and Mpzl3 knockout alleles, indicating that rc and Mpzl3 are allelic. Using a lacZ reporter gene, we detected Mpzl3 promoter activity in the companion layer and inner root sheath of the hair follicle, sebaceous gland, and epidermis. Loss of MPZL3 function also caused a striking reduction in cutaneous and overall adipose tissue. These data reveal a complex role for Mpzl3 in the control of skin development, hair growth and adipose cell functions.

Immunological memory is a hallmark of adaptive immunity, a defense mechanism endowed to vertebrates during evolution. However, an autoimmune pathogenic role of memory lymphocytes is also emerging with accumulating evidence, despite reasonable skepticism on their existence in a chronic setting of autoimmune damage. It is conceivable that autoimmune memory would be particularly harmful since memory cells would constantly “remember” and attack the body's healthy tissues. It is even more detrimental given the resistance of memory T cells to immunomodulatory therapies. In this review, we focus on self-antigen-reactive CD4+ effector memory T (TEM) cells, surveying the evidence for the role of the TEM compartment in autoimmune pathogenesis. We will also discuss the role of TEM cells in chronic and acute infectious disease settings and how they compare to their counterparts in autoimmune diseases. With their long-lasting potency, the autoimmune TEM cells could also play a critical role in anti-tumor immunity, which may be largely based on their reactivity to self-antigens. Therefore, although autoimmune TEM cells are “bad” due to their role in relentless perpetration of tissue damage in autoimmune disease settings, they are unlikely a by-product of industrial development along the modern surge of autoimmune disease prevalence. Rather, they may be a product of evolution for their “good” in clearing damaged host cells in chronic infections and malignant cells in cancer settings.

Influenza viral evolution presents a formidable challenge to vaccination due to the virus’ ability to rapidly mutate to evade immune responses. Live influenza infections generate large and diverse CD4 effector T cell responses that yield highly protective, long-lasting CD4 T cell memory that can target conserved viral epitopes. We review advances in our understanding of mechanisms involved in generating CD4 T cell responses against the influenza A virus (IAV), focusing on specialized follicular helper (TFH) and CD4 cytotoxic (ThCTL) effector subsets and on CD4 T cell memory. We also discuss two recent findings in context of enhancing vaccine responses. First, helper T cells require priming with APC secreting high levels of IL-6. Second, the transition of IAV-generated effectors to memory depends on IL-2, costimulation and antigen signals, just before effectors reach peak numbers, defined as the “memory checkpoint.” The need for these signals during the checkpoint could explain why many current influenza vaccines are poorly effective and elicit poor cellular immunity. We suggest that CD4 memory generation can be enhanced by re-vaccinating at this time. Our best hope lies in a universal vaccine that will not need to be formulated yearly against seasonal antigenically novel influenza strains and will also be protective against a pandemic strain. We suggest a vaccine approach that elicits a powerful T cell response, by initially inducing high levels of APC activation and later providing antigen at the memory checkpoint, may take us a step closer to such a universal influenza vaccine.

Naive CD4 T cell responses, especially their ability to help B cell responses, become compromised with aging. We find that using APC pre-treated ex vivo with TLR agonists, polyI:C and CpG, to prime naive CD4 T cells in vivo, restores their ability to expand and become germinal center T follicular helpers and enhances B cell IgG antibody production. Enhanced helper responses are dependent on IL-6 production by the activated APC. Aged naive CD4 T cells respond sub-optimally to IL-6 compared to the young, such that higher doses are required to induce comparable signaling. Pre-activating APC overcomes this deficiency. Responses of young CD4 T cells are also enhanced by pre-activating APC with similar effects but with only partial IL-6 dependency. Strikingly, introducing just the activated APC into aged mice significantly enhances otherwise compromised antibody production to inactivated influenza vaccine. These findings reveal a central role for production of IL-6 by APC during initial cognate interactions in the generation of effective CD4 T cell help, which becomes greater with age. Without APC activation aging CD4 T cell responses shift towards IL-6-independent Th1 and ThCTL responses. Thus, strategies that specifically activate and provide antigen to APC could potentially enhance Ab mediated protection in vaccine responses.

IntroductionA cardinal capacity of the immune system is to differentiate between "self", the body's own tissue, and "non-self", exemplified by microbial infectious agents. Malignant tumor tissues present a distinct challenge to the immune system as "altered self".Correspondence: Dr. Zhibin Chen e-mail: zchen@med.miami.edu Antigenic proteins from mutated genes in cancer cells, or viral products from transformed tumor cells, may trigger the immune system as tumor-specific antigens (TSAs) that are not expressed by nonmalignant tissues. However, for the vast majority of tumors, TSA have yet to be identified. Well-studied tumor-associated antigens (TAAs) are in fact self antigens associated with cellular differentiation [1].The difficulty to identify TSA compels a supposition that cancer cells are largely "self". The premise of cancer cells as "altered self" would predict the well-recognized association of autoimmune risk with cancer immunotherapy [2]. On the other hand, the "altered C 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2012. 42: 2584-2596 Cellular immune response 2585 self" view could also foretell autoimmunity as a beneficial effector to destroy cancer cells. In other words, although autoimmunity and tumor immunity are often viewed as being on opposite sides of the same coin, they could also be viewed to be on the same side of the coin, serving as overlapping mechanisms for tumor destruction. Indeed, the remarkable benefits of cancer immunotherapies showed in recent immunotherapy trials, most notably anti-CTLA4 antibody blockade, often came with the price of autoimmune adverse effects [3]. The intricate tangle of auto-immune toxicity and antitumor immunity substantially affects the benefit/risk ratio calculation in immunotherapies [1]. On the other hand, autoimmunity may serve to benefit clinical management of cancers. Evidence gathered from the clinics treating a variety of cancers with immunotherapies based on IL-2 [4], interferon α-2b [5], or CTLA4 [3,6] suggests that the therapy-induced autoimmunity, at least in part, may actually mediate the destruction of cancer cells. The clinical observations provoke suggestion of a paradigm shift, to which autoimmunity is not a shunned side effect, but instead an acceptable or even desirable antitumor mechanism [7]. However, it is still not well understood how self-antigen-specific T cells target tumor versus healthy tissues, and how they are regulated in tumor settings.A variety of immune suppressive mechanisms have been implicated in cancers. In the adaptive branches, Treg cells and CTLA4 are among the most prominent cellular and molecular inhibitors. Treg cells depend on CTLA4 for function [8]. CTLA4 is constitutively expressed on Treg cells but is also induced in activated Teff cells. Conditional knockout experiments indicated that CTLA4 functions predominantly through Treg cells [8]. However, other studies with CTLA4 knockout models or antibody blockade indicate that CTLA4 regulates Teff cells intrinsically and through...