Right on target: novel approaches for the direct visualization of CD1-specific T cell responses

Human Skin T Cells Express Conserved T-Cell Receptors that Cross-React with Staphylococcal Superantigens and CD1a

Human Langerhans cells highly express CD1a antigen-presenting molecules. To understand the functions of CD1a in human skin, we used CD1a tetramers to capture T cells and determine their effector functions and TCR patterns. Skin T cells from all donors showed CD1a tetramer staining, which in three cases exceeded 10% of skin T cells. CD1a tetramer-positive T cells produced diverse cytokines, including IL-2, IL-4, IL-5, IL-9, IL-17, IL-22, and IFN-γ. Conserved TCRs often recognize nonpolymorphic antigen-presenting molecules, but no TCR motifs are known for CD1a. We detected highly conserved TCRs that used TRAV34 and TRBV28 variable genes, which is a known motif for recognition of staphylococcal enterotoxin B, a superantigen associated with atopic dermatitis. We found that these conserved TCRs did not respond to superantigen presented by CD1a, but instead showed a cross-reactive response with two targets: CD1a and staphylococcal enterotoxin B presented by classical major histocompatibility complex II. These studies identify a conserved human TCR motif for CD1a-reactive T cells. Furthermore, the demonstrated cross-reaction of T cells with two common skin-specific stimuli suggests a candidate mechanism by which CD1a and skin flora could synergize during natural immune response and in Staphylococcus-associated skin diseases.

Role of natural killer T cells in liver diseases

Natural killer T (NKT) cells are a unique subset of lymphocytes, which express both T and NK cell surface markers as well as functional characteristics. They connect innate and acquired immunity, and restrictedly recognize glycolipid antigens presented by CD1d molecule. NKT cells secrete a great quantity of cytokines rapidly which regulate human immune response after being activated. For there are abundant NKT cells in human liver, researchers have a great interest in their roles.

Glycosylphosphatidylinositols in malaria pathogenesis and immunity: potential for therapeutic inhibition and vaccination

Glycosylphosphatidylinositols (GPIs) are found in the outer cell membranes of all eukaryotes. GPIs anchor a diverse range of proteins to the surface of Plasmodium falciparum, but may also exist free of protein attachment. In vitro and in vivo studies have established GPIs as likely candidate toxins in malaria, consistent with the prevailing paradigm that attributes induction of inflammatory cytokines, fever and other pathology to parasite toxins released when schizonts rupture. Although evolutionarily conserved, sufficient structural differences appear to exist that impart upon plasmodial GPIs the ability to activate second messengers in mammalian cells and elicit immune responses. In populations exposed to P. falciparum, the antibody response to purified GPIs is characterised by a predominance of immunoglobulin (Ig)G over IgM and an increase in the prevalence, level and persistence of responses with increasing age. It remains unclear, however, if these antibodies or other cellular responses to GPIs mediate anti-toxic immunity in humans; anti-toxic immunity may comprise either reduction in the severity of disease or maintenance of the malaria-tolerant state (i.e. persistent asymptomatic parasitaemia). P. falciparum GPIs are potentially amenable to specific therapeutic inhibition and vaccination; more needs to be known about their dual roles in malaria pathogenesis and protection for these strategies to succeed.

CD1 tetramers: a powerful tool for the analysis of glycolipid-reactive T cells

CD1 proteins constitute a third class of antigen-presenting molecules. They bind lipids rather than peptides, and the T cells reactive to lipids presented by CD1 have been implicated in the protection against autoimmune diseases and infectious microorganisms and in the immune surveillance for tumors. Thus, the ability to identify, purify, and track the response of CD1-reactive cells is of paramount importance. Previously existing methods for identifying these T cells were not based on TCR specificity, and therefore the data obtained by these methods were in some cases difficult to interpret. The recent generation of tetramers of alpha-galactosyl ceramide (alpha-GalCer) with CD1d has already permitted significant insight into the biology of NKT cells. Tetramers constructed from other CD1 molecules also have been obtained during the previous year. Collectively, these new reagents promise to greatly expand knowledge of the functions of lipid-reactive T cells, with potential use in monitoring the response to lipid-based vaccines and other treatments and in the diagnosis of autoimmune diseases.

Trafficking machinery of NKT cells: shared and differential chemokine receptor expression among V alpha 24(+)V beta 11(+) NKT cell subsets with distinct cytokine-producing capacity

Natural killer T (NKT) cells are important regulators of the immune system, but their trafficking machinery, including expression of chemokine receptors, has been poorly defined. Unlike other conventional T-cell populations, we show that most NKT cells express receptors for extralymphoid tissue or inflammation-related chemokines (CCR2, CCR5, and CXCR3), while few NKT cells express lymphoid tissue-homing chemokine receptors (CCR7 and CXCR5). A population with homing potential for lymph nodes (L selectin(+) CCR7(+)) exists only within a small subset of CD4 NKT cells. We show differential expression of chemokine receptors among NKT cell subsets: CCR4 is mainly expressed by a high cytokine (interleukin-4/interleukin-2)-producing (CD4) NKT subset, while CCR1, CCR6, and CXCR6 are preferentially expressed by the low cytokine-producing CD8 and CD4(-)CD8(-) subsets. In line with this, TARC/CCL17 (a CCR4 ligand) induces preferential chemotaxis of the CD4 NKT subset, while chemotactic activities of LARC/CCL20 (a CCR6 ligand) and MIP-1 alpha/CCL3 (a CCR1 ligand) are focused on the CD8 and CD4(-)CD8(-) NKT cells. We conclude that, unlike conventional naive, memory, or effector T cells, the entire NKT cell population expresses nonlymphoid tissue homing chemokine receptors, yet NKT cell subsets differ considerably from each other by displaying distinct and reciprocal expression patterns of some chemokine receptors. Our results identify chemokine receptors that are potentially important for trafficking of human blood NKT cell subsets and reveal their function (cytokine production capacity)-dependent differential trafficking potentials.