Girdhari Lal

IL-10 from marginal zone precursor B cells controls the differentiation of Th17, Tfh and Tfr cells in transplantation tolerance.

B cells are known to control CD4T cell differentiation in secondary lymphoid tissues. We hypothesized that IL-10 expression by marginal zone precursor (MZP) regulatory B cells controls the differentiation and positioning of effector and regulatory T cells during tolerization. Costimulatory blockade with donor-specific transfusion (DST) and anti-CD40L mAb in C57BL/6 mice induced tolerance to allogeneic cardiac allograft. B cell depletion or IL-10 deficiency in B cells prevented tolerance, resulting in decreased follicular regulatory CD4(+) T cells (Tfr) and increased IL-21 expression by T follicular helper (Tfh) cells in the B cell and T cell zones. IL-21 acted with IL-6 to induce CCR6(+) Th17 that caused rejection. Deficiency or blockade of IL-6, IL-21, IL-21R, or CCR6 prevented B cell depletion-induced acute cellular rejection; while agonistic mCCL20-Ig induced rejection. Adoptive transfer of IL-10(+/+) MZP in tolerogen treated CD19-Cre(+/-):IL-10(fl/fl) mice rescued the localization of Tfh and Tfr cells in the B cell follicle and prevented allograft rejection. MZP B cell IL-10 is necessary for tolerance and controls the differentiation and position of Th17, Tfh and Tfr cells in secondary lymphoid tissues. This has implications for understanding tolerance induction and how B cell depletion may prevent tolerance.

Activated mouse T cells downregulate, process and present their surface TCR to cognate anti-idiotypic CD4 + T cells

The ability of activated T cells to present foreign antigens through the MHC class II pathway has been shown in the case of human, rat and mouse T cells. In the present study, the ability of activated T cells to present their endogenous TCR in association with MHC class II molecules to CD4+ T cells was shown. Upon activation mouse T cells downregulate their surface TCR, which are degraded into peptides in endosomal/lysosomal compartments. The idiopeptides (peptides derived from the variable region of the TCR) are presented to cognate anti‐idiotypic CD4+ T cells, resulting in activation and proliferation of these cells. Interaction of idiotypic and anti‐idiotypic T cells brought about by presentation of TCR idiopeptide may have important implications for T‐cell vaccination and perpetuation of T‐cell memory not requiring persisting antigen or long‐lived memory cells.

IFN-γ promotes transendothelial migration of CD4 + T cells across the blood–brain barrier

Transendothelial migration (TEM) of Th1 and Th17 cells across the blood–brain barrier (BBB) has a critical role in the development of experimental autoimmune encephalomyelitis (EAE). How cytokines produced by inflammatory Th1 and Th17 cells damage the endothelial BBB and promote transendothelial migration of immune cells into the central nervous system (CNS) during autoimmunity is not understood. We therefore investigated the effect of various cytokines on brain endothelial cells. Among the various cytokines tested, such as Th1 (IFN‐γ, IL‐1α, IL‐1β, TNF‐α, IL‐12), Th2 (IL‐3, IL‐4, IL‐6 and IL‐13), Th17 (IL‐17A, IL‐17F, IL‐21, IL‐22, IL‐23, GM‐CSF) and Treg‐specific cytokines (IL‐10 and TGF‐β), IFN‐γ predominantly showed increased expression of ICAM‐1, VCAM‐1, MAdCAM‐1, H2‐Kb and I‐Ab molecules on brain endothelial cells. Furthermore, IFN‐γ induced transendothelial migration of CD4+ T cells from the apical (luminal side) to the basal side (abluminal side) of the endothelial monolayer to chemokine CCL21 in a STAT‐1‐dependent manner. IFN‐γ also favored the transcellular route of TEM of CD4+ T cells. Multicolor immunofluorescence and confocal microscopic analysis showed that IFN‐γ induced relocalization of ICAM‐1, PECAM‐1, ZO‐1 and VE‐cadherin in the endothelial cells, which affected the migration of CD4+ T cells. These findings reveal that the IFN‐γ produced during inflammation could contribute towards disrupting the BBB and promoting TEM of CD4+ T cells. Our findings also indicate that strategies that interfere with the activation of CNS endothelial cells may help in controlling neuroinflammation and autoimmunity.

Role of chemokine receptors and intestinal epithelial cells in the mucosal inflammation and tolerance

The intestinal epithelial lining is a very dynamic interface, where multiple interactions occur with the external world. The intestinal epithelial barrier is continuously exposed to a huge load of commensal microorganisms, food‐borne antigens, as well as invading enteropathogens. Intestinal epithelial cells (IECs) and underlying immune cells are the main players in maintaining the delicate balance between gut tolerance and inflammation. IECs deferentially express the variety of chemokines and chemokine receptors, and these receptor‐ligand interactions not only mediate the infiltration and activation of immune cells but also switch on the survival cascades in IECs. In this review, we discussed how chemokine–chemokine receptor‐induced interactions play a central role to coordinate the interplay between IECs and gut immune cells to maintain homeostasis or elicit gut inflammation. Furthermore, we discussed how chemokines and chemokine receptors were used as a target for developing new drugs and therapies to control gut inflammation and autoimmunity.

The Molecular Mechanism of Natural Killer Cells Function and Its Importance in Cancer Immunotherapy

Natural killer (NK) cells are innate immune cells that show strong cytolytic function against physiologically stressed cells such as tumor cells and virus-infected cells. NK cells show a broad array of tissue distribution and phenotypic variability. NK cells express several activating and inhibitory receptors that recognize the altered expression of proteins on target cells and control the cytolytic function. NK cells have been used in several clinical trials to control tumor growth. However, the results are encouraging only in hematological malignancies but not very promising in solid tumors. Increasing evidence suggests that tumor microenvironment regulate the phenotype and function of NK cells. In this review, we discussed the NK cell phenotypes and its effector function and impact of the tumor microenvironment on effector and cytolytic function of NK cells. We also summarized various NK cell-based immunotherapeutic strategies used in the past and the possibilities to improve the function of NK cell for the better clinical outcome.

Intratumoral natural killer cells show reduced effector and cytolytic properties and control the differentiation of effector Th1 cells

ABSTRACT Natural killer (NK) cells are known to have effector and cytolytic properties to kill virus infected or tumor cells spontaneously. Due to these properties, NK cells have been used as an adoptive cellular therapy to control tumor growth in various clinical trials but have shown limited clinical benefits. This indicates that our knowledge about phenotypic and functional differences in NK cells within the tumor microenvironment and secondary lymphoid tissues is incomplete. In this work, we report that B16F10 cell-induced melanoma recruits the CD11b+CD27+ subset of NK cells at a very early stage during tumor progression. These intratumoral NK cells showed increased expression of CD69, reduced inhibitory receptor KLRG1, and decreased proliferative ability. As compared to splenic NK cells, intratumoral NK cells showed decreased expression of activating receptors NKG2D, Ly49D and Ly49H; increased inhibitory receptors, NKG2A and Ly49A; decreased cytokines IFNγ and GM-CSF; decreased cytokine receptors IL-21R, IL-6Rα, and CD122 expression. Depletion of NK cells led to decrease peripheral as well as intratumoral effector CD4+T-bet+ cells (Th1), and increased tumor growth. Furthermore, purified NK cells showed increased differentiation of Th1 cells in an IFNγ-dependent manner. Anti-NKG2D in the culture promoted differentiation of effector Th1 cells. Collectively, these observations suggest that intratumoral NK cells possess several inhibitory functions that can be partly reversed by signaling through the NKG2D receptor or by cytokine stimulation, which then leads to increased differentiation of effector Th1 cells.

Differentiation and Transmigration of CD4 T Cells in Neuroinflammation and Autoimmunity

CD4+ T cells play a central role in orchestrating protective immunity and autoimmunity. The activation and differentiation of myelin-reactive CD4+ T cells into effector (Th1 and Th17) and regulatory (Tregs) subsets at the peripheral tissues, and their subsequent transmigration across the blood–brain barrier (BBB) into the central nervous system (CNS) parenchyma are decisive events in the pathogenesis of multiple sclerosis and experimental autoimmune encephalomyelitis. How the Th1, Th17, and regulatory Tregs transmigrate across the BBB into the CNS and cause CNS inflammation is not clearly understood. Studies with transgenic and gene knockout mice have unraveled that Th1, Th17, and Tregs play a critical role in the induction and resolution of neuroinflammation. However, the plasticity of these lineages and functional dichotomy of their cytokine products makes it difficult to understand what role CD4+ T cells in the peripheral lymphoid organs, endothelial BBB, and the CNS parenchyma play in the CNS autoimmune response. In this review, we describe some of the recent findings that shed light on the mechanisms behind the differentiation and transmigration of CD4+ T cells across the BBB into the CNS parenchyma and also highlight how these two processes are interconnected, which is crucial for the outcome of CNS inflammation and autoimmunity.

Blood–brain barrier and its function during inflammation and autoimmunity

The blood–brain barrier (BBB) is an important physiologic barrier that separates CNS from soluble inflammatory mediators and effector immune cells from peripheral circulation. The optimum function of the BBB is necessary for the homeostasis, maintenance, and proper neuronal function. The clinical and experimental findings have shown that BBB dysfunction is an early hallmark of various neurologic disorders ranging from inflammatory autoimmune, neurodegenerative, and traumatic diseases to neuroinvasive infections. Significant progress has been made in the understanding of the regulation of BBB function under homeostatic and neuroinflammatory conditions. Several neurologic disease‐modifying drugs have shown to improve the BBB function. However, they have a broad‐acting immunomodulatory function and can increase the risk of life‐threatening infections. The recent development of in vitro multicomponent 3‐dimensional BBB models coupled with fluidics chamber as well as a cell‐type specific reporter and knockout mice gave a new boost to our understanding of the dynamics of the BBB. In the review, we discuss the current understanding of BBB composition and recent findings that illustrate the critical regulatory elements of the BBB function under physiologic and inflammatory conditions, and also suggested the strategies to control BBB structure and function.

CCR6 signaling inhibits suppressor function of induced-Treg during gut inflammation

CCR6 is a G protein-coupled receptor (GPCR) that binds to a specific chemokine, CCL20. The role of CCR6-CCL20 is very well studied in the migration of immune cells, but the non-chemotaxis functions of CCR6 signaling were not known. Here, we show that during gut inflammation, the frequency of Foxp3+CD4+ T cells (Tregs) reduced in the secondary lymphoid tissues and CCR6+ Tregs enhanced the expression of RORγt. The peripheral blood mononuclear cells (PBMCs) of ulcerative colitis (UC) patients showed lower percentages of Foxp3+CD4+ T cells, as compared to healthy individuals, with CCR6+ Tregs showing higher RORγt expression as compared to CCR6-Tregs. CCL20 inhibited the TGF-β1-induced Treg (iTreg) differentiation and directed them towards the pathogenic Th17-lineage in a CCR6-dependent manner. The iTreg that differentiated in the presence of CCL20 showed lower surface expression of suppressor molecules such as CD39, CD73 and FasL, and had impaired suppressive function. Furthermore, CCR6 signaling induced phosphorylation of Akt, mTOR, and STAT3 molecules in T cells. In conclusion, we have identified a new role of CCR6 signaling in the differentiation of iTregs during inflammation and gut autoimmunity.

Development and Function of Natural Killer Cells and Its Importance in Cancer Immunotherapy

Natural killer (NK) cells are a group of innate immune cells. They show spontaneous cytolytic activity against cells under stress or infected with a virus. NK cells show a wide tissue distribution and a variable phenotype from tissue to tissue. Unlike adaptive immune cells, the cytolytic function of NK cells does not require clonal expansion. The function of NK cells is regulated by a cumulative signal received from the activating and inhibitory receptors. Mostly, expression of inhibitory receptors is controlled by genetic factors and provides tolerance to the self-tissues, whereas activation of receptor expression is controlled by environmental factors, and helps to mount the effector immune response against virus infection and tumor. NK cells isolated from the peripheral blood show antitumor cytolytic activity, which has led to several clinical trials using NK cells as adoptive cellular therapy which, however, have showed very limited success. With the advancement of or knowledge about NK cell biology, a combination of modified NK cells or NK cells in combination with other therapeutics showed better clinical output. In this review, we discuss the development of NK cells in humans and mice, various NK cell subsets and tissue distribution, an interaction of NK cells with other innate immune cells and adaptive immune cells, and the mechanism of NK cell-mediated antitumor immunity. We further discuss the use of NK cells to control tumor growth and suggested possible ways to improve the NK cell-based therapy.