Multiple checkpoints regulating finely balanced death-versus-survival decisions characterize both thymic development and peripheral homeostasis of T lymphocytes. While exploring the mechanisms of T cell death involved at various stages during the life of a T cell, we have observed and reported a variety of non-redundant roles for apoptosis inducing factor (Aif), a mitochondrial flavoprotein. Aif is ubiquitously expressed in all cell lineages and functions as an NADH oxidase in its mitochondrial location. It is released following the mitochondrial death signals, whereupon it translocates to the nucleus, binds to DNA and causes large-scale DNA fragmentation. During T cell development, Aif is important for developing thymocytes to navigate the double negative (DN)3 to DN4 transition (beta-selection), via its oxidoreductase property which protects the rapidly proliferating cells from death due to reactive oxygen species (ROS). In peripheral mature T cells, Aif deficiency leads to an increased susceptibility of T cell blasts to activation induced cell death (AICD), possibly mediated by its antioxidant function, and decreased sensitivity to neglect-induced death (NID). Thus, Aif seems to have pro-apoptotic and anti-apoptotic roles in the same lineage in different contexts and at different stages. Surprisingly, in the closely related B lymphocyte lineage, Aif deficiency does not result in any abnormality. These findings generate the possibility of specific T cell dysfunction in human disease caused by Aif deficiency, as well as in mitochondriopathies due to other causes. Also, these data raise questions regarding the basis of lineage-specific consequences of the dysfunction/deficiency of apparently ubiquitous molecules.

Following the discovery of interleukin (IL)-17 producing T helper (Th17) cells as a distinct lineage of CD4+ T helper cells it became clear that these cells play an important role in the host defense against extracellular fungal and bacterial pathogens and participate in the pathogenesis of multiple inflammatory and autoimmune disorders. Depending on the microenvironment, Th17 cells can alter their differentiation programme ultimately giving rise to either protective or pro-inflammatory pathogenic cells. We found that besides the conventional in vitro protocol for Th17 differentiation by transforming growth factor-beta (TGF-β) plus IL-6 cytokines, a combination of IL-23 plus IL-6 can also induce Th17 cells. The Th17 cells induced by IL-23 plus IL-6 (termed as effector Th17, Teff17 cells) are pathogenic upon adoptive transfer into non-obese diabetic (NOD) mice contributing to the development of type 1 diabetes (T1D) while cells induced by TGF-β plus IL-6 (termed as regulatory T cells, Treg17 cells) are non pathogenic and regulatory, and suppressed the pathogenic T cells in T1D. These cells differentially expressed a number of cytokines where Teff17 cells exhibited an increase in granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-22 whereas Treg17 cells demonstrated increased expression of IL-21 and immunosuppressive cytokine IL-10. Differentiation of Th17 cells is controlled by a transcription factor, RORγT although these cells also express variable levels of T-bet and FoxP3 transcription factors. This points to a dual functional role of Th17 subsets in autoimmune diseases particularly T1D. We suggest that similar to conventional regulatory T cells (Treg), induction of regulatory Treg17 cells could play an important role in modulating and preventing certain autoimmune diseases.

Age associated decline of the immune system continues to be a major health concern. All components of innate and adaptive immunity are adversely affected to lesser or greater extent by ageing resulting in an overall decline of immunocompetence. As a result in the aged population, there is increased susceptibility to infection, poor responses to vaccination, and increased incidence of autoreactivity. There is an increasing focus on the role of T cells during ageing because of their impact on the overall immune responses. A steady decline in the production of fresh naïve T cells, more restricted T cell receptor (TCR) repertoire and weak activation of T cells are some of the effects of ageing. In this review we summarize our present understanding of the effects of ageing on naïve CD4 T cells and potential approaches for therapeutic interventions to restore protective immunity in the aged population.

Toll-like receptors (TLRs) play a key role in the innate immune response to invading pathogens. Thus, their discovery has opened up a wide range of therapeutic possibilities for various infectious and inflammatory diseases. In the last several years, extensive research efforts have provided a considerable wealth of information on the expression and function of TLRs in the eye, with significant implications for better understanding of pathogenesis of infectious eye diseases affecting the cornea, uvea, and the retina. In this review, by using bacterial keratitis and endophthalmitis as examples, we discuss the possibilities of targeting TLR signaling for the prevention or treatment of ocular infectious diseases.

The immune system has evolved to recognize a wide range of antigenic molecules of self and non-self origin. The stimulatory antigens form complexes with antigen-presenting molecules and directly interact with the T cell receptor (TCR). Peptidic antigens associate with major histocompatibility complex (MHC) molecules and therefore, are indicated as MHC-restricted. Non-peptidic antigens do not bind to MHC molecules and are presented by other classes of antigen-presenting molecules. These non-MHC restricted antigens include glycolipid molecules, phosphorylated metabolites of the mevalonate pathway and vitamin B2 precursors. T cells specific for non-peptidic antigens have important roles in host defense against infections, autoimmunity, allergies and tumour immunosurveillance. Hence, understanding the molecular interactions between the antigen presenting cell (APC) and the T cells with non-peptidic specificity is of great relevance. Here, we review current knowledge of this type of T cells, their TCR repertoire, the structural aspects of recognized antigens, the mode of antigen recognition, and their function with special emphasis on their role in infectious diseases.

Mosquito-borne flaviviruses are a major current and emerging threat, affecting millions of people worldwide. Global climate change, combined with increasing proximity of humans to animals and mosquito vectors by expansion into natural habitats, coupled with the increase in international travel, have resulted in significant spread and concomitant increase in the incidence of infection and severe disease. Although neuroinvasive disease has been well described for some viral infections such as Japanese Encephalitis virus (JEV) and West Nile virus (WNV), others such as dengue virus (DENV) have recently displayed an emerging pattern of neuroinvasive disease, distinct from the previously observed, systemically-induced encephalomyelopathy. In this setting, the immune response is a crucial component of host defence, in preventing viral dissemination and invasion of the central nervous system (CNS). However, subversion of the anti-viral activities of macrophages by flaviviruses can facilitate viral replication and spread, enhancing the intensity of immune responses, leading to severe immune-mediated disease which may be further exacerbated during the subsequent infection with some flaviviruses. Furthermore, in the CNS myeloid cells may be responsible for inducing specific inflammatory changes, which can lead to significant pathological damage during encephalitis. The interaction of virus and cells of the myeloid lineage is complex, and this interaction is likely responsible at least in part, for crucial differences between viral clearance and pathology. Recent studies on the role of myeloid cells in innate immunity and viral control, and the mechanisms of evasion and subversion used by flaviviruses are rapidly advancing our understanding of the immunopathological mechanisms involved in flavivirus encephalitis and will lead to the development of therapeutic strategies previously not considered.

Sialic acids (Sias) are nine-carbon keto sugars primarily present on the terminal residue of cell surface glycans. Sialic acid binding immunoglobulins (Ig)-like lectins (siglecs) are generally expressed on various immune cells. They selectively recognize different linkage-specific sialic acids and undertake a variety of cellular functions. Many pathogens either synthesize or acquire sialic acids from the host. Sialylated pathogens generally use siglecs to manipulate the host immune response. The present review mainly deals with the newly developed information regarding mechanism of acquisition of sialic acids by pathogens and their biological relevance especially in the establishment of successful infection by impairing host innate immunity. The pathogens which are unable to synthesize sialic acids might adsorb these from the host as a way to engage the inhibitory siglecs. They promote association with the immune cells through sialic acids-siglec dependent manner. Such an association plays an important role to subvert host's immunity. Detailed investigation of these pathways has been discussed in this review. Particular attention has been focused on Pseudomonas aeruginosa (PA) and Leishmania donovani.

Studies on host genomics have revealed the existence of identifiable HIV-1 specific protective factors among infected individuals who remain naturally resistant viraemia controllers with little or no evidence of virus replication. These factors are broadly grouped into those that are immune associated (MHC, chemokines, cytokines, CTLs and others), linked to viral entry (chemokine co-receptors and ligands), act as post-entry restriction elements (TRIM5a, APOBEC3) and those associated with viral replication (cytokines and others). These features have been identified through multiple experimental approaches ranging from candidate gene approaches, genome wide association studies (GWAS), expression analysis in conjunction with functional assays in humans to primate based models. Several studies have highlighted the individual and population level gross differences both in the viral clade sequences as well as host determined genetic associations. This review collates current information on studies involving major histocompatibility complex (MHC) as well as non MHC genes in the context of HIV-1 infection and AIDS involving varied ethnic groups. Special focus of the review is on the genetic studies carried out on the Indian population. Further challenges with regard to therapeutic interventions based on current knowledge have been discussed along with discussion on documented cases of stem cell therapy and very early highly active antiretroviral therapy (HAART) interventions.

HIV continues to be a major health problem worldwide even today. Owing to the intricate nature of its interactions with the immune system, HIV has remained an enigma that cleverly utilizes the host machinery to survive. Its ability to evade the host immune system, at both levels, innate and adaptive, allows the pathogen to replicate and transmit from one host to another. It has been shown that HIV has multipronged effects especially on the adaptive immunity, with CD4+ T cells being the worst affected T cell populations. Various analyses have revealed that the exposure to HIV results in clonal expansion and excessive activation of the immune system. Also, an abnormal process of differentiation has been observed suggestive of an alteration and blocks in the maturation of various T cell subsets. Additionally, HIV has shown to accelerate immunosenescence and exhaustion of the overtly activated T cells. Apart from causing phenotypic changes, HIV has adverse effects on the functional aspect of the immune system, with evidences implicating it in the loss of the capacity of T cells to secrete various antiviral cytokines and chemokines. However, there continues to be many aspects of the immunopathogenesis of HIV that are still unknown and thus require further research to convert the malaise of HIV into a manageable epidemic.

Chronic hepatitis B virus (HBV) infection affects millions of people worldwide and about a half million people die every year. India represents the second largest pool of chronic HBV infection worldwide with an estimated 40 million infected people. The prevalence of chronic HBV infection in pregnant women is shown to be 0.82 per cent with the risk of mother-to-child vertical transmission. Hepatitis B e antigen (HBeAg) positivity indicates replicative form of HBV which may play a role in immunotolerance in utero by crossing the placenta. In case of HBeAg positivity and high viral load of mother, HBV immunoglobulin is preferably given along with HBV vaccination. Antiviral therapy is recommended for use in the third trimester of pregnancy to reduce the perinatal transmission of HBV, however, use of antiviral therapy should be individualized during pregnancy. Chronic HBV infection in neonates is linked with strong presence of Tregs (T regulatory cells) and defective CD8 T cells pool to produce interferon (IFN)-γ. T cell receptor (TCRζ) chain defects were also associated with decreased CD8 T cell dysfunction. Decreased TCRζ expression could be due to persistent intrauterine exposure of the viral antigens early in embryonic development leading to immune tolerance to HBV antigens in the newborns positive for hepatitis B surface antigen (HBsAg+ve). Therefore, due to HBV infection, T cell tolerance to HBV-antigen may probably leave the newborn as a chronic carrier. However, HBV vaccination may have benefits in restoring acquired immunity and better production of HBV specific antibodies.

Dendritic cells (DCs) play an important role in both immunological tolerance and immunity as well as in pro- and anti-inflammatory responses. Upon uptake of apoptotic cells and apoptotic bodies, DCs degrade self antigens from them and induce anti-inflammatory response and T regulatory (Treg) cells resulting in the maintenance of tolerance to self antigens. Ageing is characterized by progressive immunodeficiency, inflammation, and autoimmunity. In this paper we will review the role of DCs in inflammation and autoimmunity in human ageing and will highlight the observations that DCs from aged humans display impairment in their capacity to uptake apoptotic cells, and paradoxically induce proinflammatory response and increased reactivity to self antigen (DNA). DNA from aged is hypomethylated and hypomethylation is associated with increased immunogenecity of self DNA.

Susceptibility to autoimmunity is determined by multiple factors. Defining the contribution of the quantitative versus qualitative aspects of antigen-directed immune responses as well as the factors influencing target organ susceptibility is vital to advancing the understanding of the pathogenesis of autoimmunity. In a series of studies, we have addressed these issues using the adjuvant-induced arthritis (AA) model of human rheumatoid arthritis (RA). Lewis rats are susceptible to AA following immunization with heat-killed Mycobacterium tuberculosis H37Ra, whereas Wistar-Kyoto (WKY) rats of the same MHC (major histocompatibility complex) haplotype are resistant. Comparative studies on these and other susceptible/resistant rodent strains have offered interesting insights into differential cytokine responses in the face of comparable T cell proliferative response to the disease relevant antigens. Study of the cytokine kinetics have also permitted validation of the disease-protective versus disease-aggravating effects of specific cytokines by treatment of rats/mice with those cytokines at different phases of the disease. In regard to the target organ attributes, the migration of arthritogenic leukocytes into the joints; the expression of mediators of inflammation, angiogenesis, and tissue damage; the role of vascular permeability; and the characteristics of vascular endothelial cells have been examined. Further, various inhibitors of angiogenesis are effective in suppressing arthritis. Taken together, the differential cytokine responses and unique attributes of the target organ have revealed novel aspects of disease susceptibility and joint damage in AA. The translation of this basic research in animal models to RA patients would not only advance our understanding of the disease process, but also offer novel avenues for immunomodulation of this disease.

Rheumatoid arthritis (RA) is a multifactorial disease and requires interaction between genetic and environmental factors for predisposition. The presence of bacterial DNA of the gut residing commensals in synovium as well as dysbiosis of certain commensal bacteria in faecal samples of RA patients as compared to controls suggest a significant role of the gut flora in pathogenesis of RA. The gut commensals are involved in host immune development and function suggesting they might be critical epigenetic factors modifying autoimmune diseases like RA. This raises the question if gut-derived commensal can be exploited to generate a biomarker profile along with genetic factors to define individuals at risk. Genomic wide association studies have confirmed the HLA (human leukocyte antigen) class II genes as the strongest risk factor for predisposition to RA. HLA-DQ8 and DRB1*0401 molecules predispose to develop arthritis while DRB1*0402 provides protection. Interaction between host genetic factors like major histocompatibility complex (MHC) and gut microbiota and its impact on the development of RA is difficult to study in humans due to high variability in the genetic factors and diet. Animal models provide a means to study the molecular basis of pathogenesis thereby providing a basis for developing therapeutic strategies. Using transgenic mice expressing RA-associated and resistant HLA genes, we have developed a collagen-induced arthritis (CIA) model that shares similarities with human disease in sex-bias, autoantibody profile and phenotype. Studies in transgenic mice suggest that arthritis-susceptibility may be associated with dysbiosis in the gut microbiome. Studies in animal models underscore the impact of the gut flora in extra-intestinal diseases. Exploring the role of gut microbes will significantly advance our understanding of RA pathogenesis and may further help develop strategies for mucosal modulation of RA.

Background & objectives: In spite of the fact that BCG is the most widely used vaccine, tuberculosis (TB) continues to be a major killer disease in TB-endemic regions. Recently, many emerging evidences from the published literature indicate the role of environmental mycobacteria in blocking the processing and presentation of BCG antigens and thereby impairing with suboptimal generation of protective T cells. To surmount this problem associated with BCG, we constructed a novel lipopeptide (L91) by conjugating a promiscuous peptide consisting of CD4 ⁺ T-helper epitope of sequence of 91-110 of 16 kDa antigen of Mycobacterium tuberculosis to Pam2Cys, an agonist of Toll-like receptor-2. Methods: Mice were immunized subcutaneously with 20 nmol of L91, followed by a booster with 10 nmol, after an interval of 21 days of primary immunization. Animals were sacrificed after seven days of post-booster immunization. L91 induced immune response was characterized by the expression of MHC-II and CD74 on the surface of dendritic cells (DCs) by flowcytometry. Cytokines (IL-4, IL-10, IFN-γ) secretion and anti-peptide antibodies were measured by ELISA. Results: Self-adjuvanting lipopeptide vaccine (L91) was directly bound to MHC-II molecules and without requiring extensive processing for its presentation to T cells. It stimulated and activated dendritic cells and augmented the expression of MHC-II molecules. Further, it activated effector CD4 T cells to mainly secrete interferon (IFN)-γ but not interleukin (IL)-4 and IL-10. L91 did not elicit anti-peptide antibodies. Interpretation & conclusions: The findings suggest that L91 evokes maturation and upregulation of MHC class II molecules and promotes better antigen presentation and, therefore, optimum activation of T cells. L91 mainly induces effector Th1 cells, as evidenced by predominant release of IFN-γ, consequently can mount favourable immune response against M. tuberculosis . As L91 does not provoke the generation of anti-peptide antibodies, there is no fear of the efficacy of the vaccine being neutralized by pre-existing anti-mycobacterial antibodies in TB-endemic population. In conclusion, L91 may be considered as a future potential candidate vaccine against TB.

The development of regenerative medicine relies in part on the capacity of stem cells to differentiate into specialized cell types and reconstitute tissues and organs. The origin of the stem cells matters. While autologous cells were initially the preferred ones the need for "off the shelf" cells is becoming prevalent. These cells will be immediately available and they originate from young non diseased individuals. However their allogenicity can be viewed as a limitation to their use. Recent works including our own show that allogenicity of stem cell can be viewed as on one hand detrimental leading to their elimination and on the other hand beneficial through a paracrine effect that can induce a local tissue regenerative effect from endogenous stem cells. Also their immune modulatory capacity can be harnessed to favor regeneration. Therefore the immune phenotype of stem cells is an important criteria to be considered before their clinical use. Immuno monitoring of the consequences of their in vivo injection needs to be taken into account. Transplantation immunology knowledge will be instrumental to enable the development of safe personalized regenerative stem cell therapy.

γδ T lymphocytes represent a minor subset of peripheral blood in humans (<10%). γδ T cells expressing Vγ9Vδ2 T cell receptor recognise the endogenous pool of isopentenyl pyrophosphate (IPP) that is overproduced in cancer cells as a result of dysregulated mevalonate pathway. Aminobisphosphonates increase the endogenous pool of IPP in cells by blocking the enzyme farnesyl pyrophosphate synthase (FPPS) of the mevalonate pathway. Activated γδ T cells release copious amounts of interferon (IFN)-γ and tumour necrosis factor (TNF)-α and exhibit potent anti-tumour activity. Combination of γδ T cells with therapeutic monoclonal antibodies can efficiently mediate antibody dependent cellular cytotoxicity against tumours. These features makes γδ T cells attractive mediator of cancer immunotherapy. We review here, the basic properties and importance of γδ T cells in tumour immunity, and highlight the key advances in anti-tumour effector functions of γδ T cells achieved over the last few years and also summarize the results of the clinical trials that have been done till date. Future immunotherapeutic approach utilizing γδ T cells holds considerable promise for treatment of different types of cancer.

Chikungunya virus, a re-emerging mosquito-borne alphavirus, causes fever, rash and persistent arthralgia/arthritis in humans. Severe outbreaks have occurred resulting in infections of millions of people in Southeast Asia and Africa. Currently there are no antiviral drugs or vaccines for prevention and treatment of chikungunya infections. Herein we report the current status of research on antiviral drugs and vaccines for chikungunya virus infections.

Chronic hepatitis C infection poses a major global health predicament and appears to be potent threat to mankind. The treatment in wide use is interferon/ribavirin combination therapy which is generally effective in about 60-70 per cent of patients carrying genotype 3 and causes significant morbidity. The response to therapy is largely guided by limited number of factors such as genotype of virus, rapid virological response, ethnicity, pre-therapy viral load, etc. While involvement of host genetic factors has been a major focus of research in playing an important role in the outcome of disease, the role of immune system cannot be marginalized. Poor cellular trafficking and suboptimal T cell responses in liver, the hall marks of chronic hepatitis C virus infection, might be attributed to defective antigen presentation. Various immunological factors, both innate and adaptive, play role in the pathogenesis of the disease and become dysfunctional in active disease. Recent reports suggest the major impact of functional and numerical status of dendritic cells in deciding the fate of antiviral therapy. In this review we take a look at the involvement of dendritic cells in playing an important role in the response to therapy.

The pure recombinant and synthetic antigens used in modern day vaccines are generally less immunogenic than older style live/attenuated and killed whole organism vaccines. One can improve the quality of vaccine production by incorporating immunomodulators or adjuvants with modified delivery vehicles viz. liposomes, immune stimulating complexes (ISCOMs), micro/nanospheres apart from alum, being used as gold standard. Adjuvants are used to augment the effect of a vaccine by stimulating the immune system to respond to the vaccine, more vigorously, and thus providing increased immunity to a particular disease. Adjuvants accomplish this task by mimicking specific sets of evolutionary conserved molecules which include lipopolysaccharides (LPS), components of bacterial cell wall, endocytosed nucleic acids such as dsRNA, ssDNA and unmethylated CpG dinucleotide containing DNA. This review provides information on various vaccine adjuvants and delivery vehicles being developed to date. From literature, it seems that the humoral immune responses have been observed for most adjuvants and delivery platforms while viral-vector, ISCOMs and Montanides have shown cytotoxic T-cell response in the clinical trials. MF59 and MPL^® have elicited Th1 responses, and virus-like particles (VLPs), non-degradable nanoparticle and liposomes have also generated cellular immunity. Such vaccine components have also been evaluated for alternative routes of administration with clinical success reported for intranasal delivery of viral-vectors and proteosomes and oral delivery of VLP vaccines.

Stem cell and organ transplantation are considered as the major advances of modern medicine. Unfortunately the success of transplantation is limited by its toxicity and infectious complications as a result of profound immunosuppression. Viral infections are an extremely common and predictable problem in these patients. Antiviral drugs given either prophylactically or as early therapy for patients with detectable viral loads appear to be an effective strategy for reducing viral infections. However, long-term treatment with these drugs is associated with significant toxicity, expense and the appearance of drug resistant virus isolates ultimately resulting in treatment failure. Over the last few years, there is increasing evidence that cellular immune therapies can reverse the outgrowth of haematological malignancies and can also provide therapeutic benefit against lethal viral infections. While the expansion and adoptive transfer of virus-specific T-cells from the healthy donor can be an effective strategy to control viral replication, this is not possible when donors are seronegative or are subsequently inaccessible. Recent studies have demonstrated successful expansion of virus-specific T-cells from seropositive stem cell transplant recipients of a seronegative graft with active virus disease and the long term reconstitution of protective anti-viral immunity following their adoptive transfer back into the patients. Furthermore, this immunotherapeutic strategy has also been extended for multiple pathogens including cytomegalovirus, Epstein-Barr virus, adenovirus and BK polyoma-virus. This approach can be employed to rapidly expand multiple pathogens-specific T cells that can be used for adoptive immunotherapy. Finally, new assays to monitor T cell immunity have been developed which will allow to identify the high risk transplant patients who may develop virus-associated complications post-transplantation and can be given adoptive T cell therapy prophylactically.

Accumulating evidences indicate that some diseases are triggered by abnormalities of the gut microbiota. Among these, immune-related diseases can be the promising targets for probiotcs. Several studies have proved the efficacy of probiotics for preventing such diseases including cancers, infections, allergies, inflammatory bowel diseases and autoimmune diseases. Lactobacillus casei strain Shirota (LcS) is one of the most popular probiotics, benefits of which in health maintenance and disease control have been supported by several science-based evidences. This review summarizes human clinical trials with this probiotic against cancer development and also discusses the possible immunomodulatory mechanisms by which LcS exerts anti-cancer activity.