TCR-mediated recognition of glycolipid CD1 complexes

Antitumor immunostimulatory activity of the traditional Chinese medicine polysaccharide on hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a prevalent malignancy, often associated with compromised immune function in affected patients. This can be attributed to the secretion of specific factors by liver cancer cells, which hinder the immune response and lead to a state of immune suppression. Polysaccharides derived from traditional Chinese medicine (TCM) are valuable constituents known for their immunomodulatory properties. This review aims to look into the immunomodulatory effects of TCM polysaccharides on HCC. The immunomodulatory effects of TCM polysaccharides are primarily manifested through the activation of effector T lymphocytes, dendritic cells, NK cells, and macrophages against hepatocellular carcinoma (HCC) both in vivo and in vitro settings. Furthermore, TCM polysaccharides have demonstrated remarkable adjuvant antitumor immunomodulatory effects on HCC in clinical settings. Therefore, the utilization of TCM polysaccharides holds promising potential for the development of novel therapeutic agents or adjuvants with advantageous immunomodulatory properties for HCC.

Molecules in medicine mini review: the αβ T cell receptor

As an integral part of the mammalian immune system, a distributed network of tissues, cells, and extracellular factors, T lymphocytes perform and control a multitude of activities that collectively contribute to the effective establishment, maintenance, and restoration of tissue and organismal integrity. Development and function of T cells is controlled by the T cell receptor (TCR), a heterodimeric cell surface protein uniquely expressed on T cells. During T cell development, the TCR undergoes extensive somatic diversification that generates a diverse T cell repertoire capable of recognizing an extraordinary range of protein and nonprotein antigens presented in the context of major histocompatibility complex molecules (MHC). In this review, we provide an introduction to the TCR, describing underlying principles that position this molecule as a central regulator of the adaptive immune system involved in responses ranging from tissue protection and preservation to pathology and autoimmunity.

Microbial exposure during early life has persistent effects on natural killer T cell function

Exposure to microbes during early childhood is associated with protection from immune-mediated diseases such as inflammatory bowel disease (IBD) and asthma. Here, we show that in germ-free (GF) mice, invariant natural killer T (iNKT) cells accumulate in the colonic lamina propria and lung, resulting in increased morbidity in models of IBD and allergic asthma as compared with that of specific pathogen-free mice. This was associated with increased intestinal and pulmonary expression of the chemokine ligand CXCL16, which was associated with increased mucosal iNKT cells. Colonization of neonatal-but not adult-GF mice with a conventional microbiota protected the animals from mucosal iNKT accumulation and related pathology. These results indicate that age-sensitive contact with commensal microbes is critical for establishing mucosal iNKT cell tolerance to later environmental exposures.

The 2.5 Å structure of CD1c in complex with a mycobacterial lipid reveals an open groove ideally suited for diverse antigen presentation

CD1 molecules function to present lipid-based antigens to T cells. Here we present the crystal structure of CD1c at 2.5 Å resolution, in complex with the pathogenic Mycobacterium tuberculosis antigen mannosyl-β1-phosphomycoketide (MPM). CD1c accommodated MPM's methylated alkyl chain exclusively in the A' pocket, aided by a unique exit portal underneath the α1 helix. Most striking was an open F' pocket architecture lacking the closed cavity structure of other CD1 molecules, reminiscent of peptide binding grooves of classical major histocompatibility complex molecules. This feature, combined with tryptophan-fluorescence quenching during loading of a dodecameric lipopeptide antigen, provides a compelling model by which both the lipid and peptide moieties of the lipopeptide are involved in CD1c presentation of lipopeptides.

Synthesis and evaluation of 3''- and 4''-deoxy and -fluoro analogs of the immunostimulatory glycolipid, KRN7000

Four 3''- and 4''-deoxy and -fluorogalactosyl ceramides were synthesized, and their ability to stimulate iNKT cells, based on levels of IL-2 production, was assessed in three NKT cell receptor hybridomas. In two of the hybridomas, 1.2 and 2H4, all of the analogs were immunostimulatory, while in the 1.4 hybridoma only the 4''-fluoro analog led to the production of significant levels of IL-2.

Human innate Mycobacterium tuberculosis-reactive alphabetaTCR+ thymocytes

The control of Mycobacterium tuberculosis (Mtb) infection is heavily dependent on the adaptive Th1 cellular immune response. Paradoxically, optimal priming of the Th1 response requires activation of priming dendritic cells with Th1 cytokine IFN-γ. At present, the innate cellular mechanisms required for the generation of an optimal Th1 T cell response remain poorly characterized. We hypothesized that innate Mtb-reactive T cells provide an early source of IFN-γ to fully activate Mtb-exposed dendritic cells. Here, we report the identification of a novel population of Mtb-reactive CD4⁻ αβTCR⁺ innate thymocytes. These cells are present at high frequencies, respond to Mtb-infected cells by producing IFN-γ directly ex vivo, and display characteristics of effector memory T cells. This novel innate population of Mtb-reactive T cells will drive further investigation into the role of these cells in the containment of Mtb following infectious exposure. Furthermore, this is the first demonstration of a human innate pathogen-specific αβTCR⁺ T cell and is likely to inspire further investigation into innate T cells recognizing other important human pathogens.

Mycobacterium tuberculosis (Mtb) infects about one-third of the world's population. Most people who are exposed remain healthy, but control of this intracellular bacterium requires a robust cellular immune response. Production of the pro-inflammatory cytokine IFN-γ from cells in the adaptive immune response is critically important in the immune control of Mtb. However, this cytokine is also essential in initiating an optimal adaptive immune response. We hypothesized that innate cells could provide an early source of IFN-γ to aid in generation of an optimal adaptive immune response. We looked for IFN-γ producing cells in human neonates that were unlikely to have been previously exposed to either Mtb or other environmental mycobacteria. Here, we report the identification of a novel T cell population from the thymus that produces IFN-γ in response to Mtb-infected cells. Mtb-reactive thymocytes are present at high frequencies, are present in nearly all newborns tested, and display characteristics of T cells normally associated with a memory response. This novel innate population of Mtb-reactive cells will drive further investigation into the role of these cells in the containment of Mtb following infectious exposure and is likely to inspire further investigation into innate T cells recognizing other important human pathogens.

Evolutionarily conserved amino acids that control TCR-MHC interaction

The rules for the conserved reaction of alphabeta T cell receptors (TCRs) with major histocompatibility complex (MHC) proteins plus peptides are poorly understood, probably because thymocytes bearing TCRs with the strongest MHC reactivity are lost by negative selection. Thus, only TCRs with an attenuated ability to react with MHC appear on mature T cells. Also, the interaction sites between TCRs and MHC may be inherently flexible and hence difficult to spot. We reevaluated contacts between TCRs and MHC in the solved structures of their complexes with these points in mind. Relatively conserved amino acids in the TCR complementarity-determining regions (CDR) 1 and CDR2 are often used to bind exposed areas of the MHC alpha-helices. These areas are exposed because of small amino acids that allow somewhat flexible binding of the TCRs. The TCR amino acids involved are specific to families of variable (V) regions and to some extent different rules may govern the recognition of MHCI versus MHCII.