Meenu Sharma

Surface Structure Characterization of Aspergillus fumigatus Conidia Mutated in the Melanin Synthesis Pathway and Their Human Cellular Immune Response

ABSTRACT In Aspergillus fumigatus, the conidial surface contains dihydroxynaphthalene (DHN)-melanin. Six-clustered gene products have been identified that mediate sequential catalysis of DHN-melanin biosynthesis. Melanin thus produced is known to be a virulence factor, protecting the fungus from the host defense mechanisms. In the present study, individual deletion of the genes involved in the initial three steps of melanin biosynthesis resulted in an altered conidial surface with masked surface rodlet layer, leaky cell wall allowing the deposition of proteins on the cell surface and exposing the otherwise-masked cell wall polysaccharides at the surface. Melanin as such was immunologically inert; however, deletion mutant conidia with modified surfaces could activate human dendritic cells and the subsequent cytokine production in contrast to the wild-type conidia. Cell surface defects were rectified in the conidia mutated in downstream melanin biosynthetic pathway, and maximum immune inertness was observed upon synthesis of vermelone onward. These observations suggest that although melanin as such is an immunologically inert material, it confers virulence by facilitating proper formation of the A. fumigatus conidial surface.

Circulating human basophils lack the features of professional antigen presenting cells

Recent reports in mice demonstrate that basophils function as antigen presenting cells (APC). They express MHC class II and co-stimulatory molecules CD80 and CD86, capture and present soluble antigens or IgE-antigen complexes and polarize Th2 responses. Therefore, we explored whether human circulating basophils possess the features of professional APC. We found that unlike dendritic cells (DC) and monocytes, steady-state circulating human basophils did not express HLA-DR and co-stimulatory molecules CD80 and CD86. Basophils remained negative for these molecules following stimulation with soluble Asp f 1, one of the allergens of Aspergillus fumigatus; Bet v 1, the major birch allergen; TLR2-ligand or even upon IgE cross-linking. Unlike DC, Asp f 1-pulsed basophils did not promote Th2 responses as analyzed by the secretion of IL-4 in the basophil-CD4+ T cell co-culture. Together, these results demonstrate the inability of circulating human basophils to function as professional APC.

Intravenous Gammaglobulin Inhibits Encephalitogenic Potential of Pathogenic T Cells and Interferes with their Trafficking to the Central Nervous System, Implicating Sphingosine-1 Phosphate Receptor 1–Mammalian Target of Rapamycin Axis

Despite an increasing use of high-dose therapy of i.v. gammaglobulin (IVIg) in the treatment of various T cell– and Ab-mediated inflammatory and autoimmune diseases, comprehension of the mechanisms underlying its therapeutic benefit has remained a major challenge. Particularly, the effect of IVIg in T cell–mediated autoimmune conditions remains unexplored. Using an actively induced experimental autoimmune encephalomyelitis model, a T cell–mediated autoimmune condition, we demonstrate that IVIg inhibits the differentiation of naive CD4 T cells into encephalitogenic subsets (Th1 and Th17 cells) and concomitantly induces an expansion of Foxp3+ regulatory T cells. Further, IVIg renders effector T cells less pathogenic by decreasing the expression of encephalitogenic molecular players like GM-CSF and podoplanin. Intriguingly and contrary to the current arguments, the inhibitory FcγRIIB is dispensable for IVIg-mediated reciprocal modulation of effector and regulatory CD4 subsets. Additionally, F(ab′)2 fragments also retained this function of IVIg. IVIg or F(ab′)2 fragments decrease the sphingosine-1 phosphate receptor on CD4 cells, thus sequestering these cells in the draining lymph nodes and decreasing their infiltration into the CNS. Our study reveals a novel role of Igs in the modulation of polarization and trafficking of T lymphocytes, accounting for the observed beneficial effect in IVIg therapy.

Human B cells induce dendritic cell maturation and favour Th2 polarization by inducing OX-40 ligand

Dendritic cells (DCs) play a critical role in immune homeostasis by regulating the functions of various immune cells, including T and B cells. Notably, DCs also undergo education on reciprocal signalling by these immune cells and environmental factors. Various reports demonstrated that B cells have profound regulatory functions, although only few reports have explored the regulation of human DCs by B cells. Here we demonstrate that activated but not resting B cells induce maturation of DCs with distinct features to polarize Th2 cells that secrete interleukin (IL)-5, IL-4 and IL-13. B-cell-induced maturation of DCs is contact dependent and implicates signalling of B-cell activation molecules CD69, B-cell-activating factor receptor, and transmembrane activator and calcium-modulating cyclophilin ligand interactor. Mechanistically, differentiation of Th2 cells by B-cell-matured DCs is dependent on OX-40 ligand. Collectively, our results suggest that B cells have the ability to control their own effector functions by enhancing the ability of human DCs to mediate Th2 differentiation.

THPdb: Database of FDA-approved peptide and protein therapeutics

THPdb (http://crdd.osdd.net/raghava/thpdb/) is a manually curated repository of Food and Drug Administration (FDA) approved therapeutic peptides and proteins. The information in THPdb has been compiled from 985 research publications, 70 patents and other resources like DrugBank. The current version of the database holds a total of 852 entries, providing comprehensive information on 239 US-FDA approved therapeutic peptides and proteins and their 380 drug variants. The information on each peptide and protein includes their sequences, chemical properties, composition, disease area, mode of activity, physical appearance, category or pharmacological class, pharmacodynamics, route of administration, toxicity, target of activity, etc. In addition, we have annotated the structure of most of the protein and peptides. A number of user-friendly tools have been integrated to facilitate easy browsing and data analysis. To assist scientific community, a web interface and mobile App have also been developed.

Intravenous immunoglobulin-induced IL-33 is insufficient to mediate basophil expansion in autoimmune patients

Intravenous immunoglobulin (IVIg) is used in the therapy of various autoimmune and inflammatory diseases. Recent studies in experimental models propose that anti-inflammatory effects of IVIg are mainly mediated by α2,6-sialylated Fc fragments. These reports further suggest that α2,6-sialylated Fc fragments interact with DC-SIGN+ cells to release IL-33 that subsequently expands IL-4-producing basophils. However, translational insights on these observations are lacking. Here we show that IVIg therapy in rheumatic patients leads to significant raise in plasma IL-33. However, IL-33 was not contributed by human DC-SIGN+ dendritic cells and splenocytes. As IL-33 has been shown to expand basophils, we analyzed the proportion of circulating basophils in these patients following IVIg therapy. In contrast to mice data, IVIg therapy led to basophil expansion only in two patients who also showed increased plasma levels of IL-33. Importantly, the fold-changes in IL-33 and basophils were not correlated and we could hardly detect IL-4 in the plasma following IVIg therapy. Thus, our results indicate that IVIg-induced IL-33 is insufficient to mediate basophil expansion in autoimmune patients. Hence, IL-33 and basophil-mediated anti-inflammatory mechanism proposed for IVIg might not be pertinent in humans.

Mycobacteria-responsive sonic hedgehog signaling mediates programmed death-ligand 1-and prostaglandin E 2 -induced regulatory T cell expansion

CD4+CD25+FoxP3+ regulatory T cells (Tregs) are exploited by mycobacteria to subvert the protective host immune responses. The Treg expansion in the periphery requires signaling by professional antigen presenting cells and in particularly dendritic cells (DC). However, precise molecular mechanisms by which mycobacteria instruct Treg expansion via DCs are not established. Here we demonstrate that mycobacteria-responsive sonic hedgehog (SHH) signaling in human DCs leads to programmed death ligand-1 (PD-L1) expression and cyclooxygenase (COX)-2-catalyzed prostaglandin E2 (PGE2) that orchestrate mycobacterial infection-induced expansion of Tregs. While SHH-responsive transcription factor GLI1 directly arbitrated COX-2 transcription, specific microRNAs, miR-324-5p and miR-338-5p, which target PD-L1 were downregulated by SHH signaling. Further, counter-regulatory roles of SHH and NOTCH1 signaling during mycobacterial-infection of human DCs was also evident. Together, our results establish that Mycobacterium directs a fine-balance of host signaling pathways and molecular regulators in human DCs to expand Tregs that favour immune evasion of the pathogen.

Antibody-mediated catalysis: induction and therapeutic relevance.

Abzymes are immunoglobulins endowed with enzymatic activities. The catalytic activity of an abzyme resides in the variable domain of the antibody, which is constituted by the close spatial arrangement of amino acid residues involved in catalysis. The origin of abzymes is conferred by the innate diversity of the immunoglobulin gene repertoire. Under deregulated immune conditions, as in autoimmune diseases, the generation of abzymes to self-antigens could be deleterious. Technical advancement in the ability to generate monoclonal antibodies has been exploited in the generation of abzymes with defined specificities and activities. Therapeutic applications of abzymes are being investigated with the generation of monoclonal abzymes against several pathogenesis-associated antigens. Here, we review the different contexts in which abzymes are generated, and we discuss the relevance of monoclonal abzymes for the treatment of human diseases.

Computer-aided designing of immunosuppressive peptides based on IL-10 inducing potential

In the past, numerous methods have been developed to predict MHC class II binders or T-helper epitopes for designing the epitope-based vaccines against pathogens. In contrast, limited attempts have been made to develop methods for predicting T-helper epitopes/peptides that can induce a specific type of cytokine. This paper describes a method, developed for predicting interleukin-10 (IL-10) inducing peptides, a cytokine responsible for suppressing the immune system. All models were trained and tested on experimentally validated 394 IL-10 inducing and 848 non-inducing peptides. It was observed that certain types of residues and motifs are more frequent in IL-10 inducing peptides than in non-inducing peptides. Based on this analysis, we developed composition-based models using various machine-learning techniques. Random Forest-based model achieved the maximum Matthews’s Correlation Coefficient (MCC) value of 0.59 with an accuracy of 81.24% developed using dipeptide composition. In order to facilitate the community, we developed a web server “IL-10pred”, standalone packages and a mobile app for designing IL-10 inducing peptides (http://crdd.osdd.net/raghava/IL-10pred/).

Autoimmunity: Basophils in autoimmune and inflammatory diseases

Basophils are classically known for their pathogenic role in asthma and allergic skin conditions. However, reports suggest that basophil activation mediated by autoreactive IgE, thymic stromal lymphopoietin or Toll-like receptors has an important role in the pathogenesis of lupus nephritis, eosinophilic oesophagitis and IgG4-related diseases, respectively.