Isolation of a Structural Mechanism for Uncoupling T Cell Receptor Signaling from Peptide-MHC Binding.

TCR-signaling strength generally correlates with peptide-MHC binding affinity; however, exceptions exist. We find high-affinity, yet non-stimulatory, interactions occur with high frequency in the human T cell repertoire. Here, we studied human TCRs that are refractory to activation by pMHC ligands despite robust binding. Analysis of 3D affinity, 2D dwell time, and crystal structures of stimulatory versus non-stimulatory TCR-pMHC interactions failed to account for their different signaling outcomes. Using yeast pMHC display, we identified peptide agonists of a formerly non-responsive TCR. Single-molecule force measurements demonstrated the emergence of catch bonds in the activating TCR-pMHC interactions, correlating with exclusion of CD45 from the TCR-APC contact site. Molecular dynamics simulations of TCR-pMHC disengagement distinguished agonist from non-agonist ligands based on the acquisition of catch bonds within the TCR-pMHC interface. The isolation of catch bonds as a parameter mediating the coupling of TCR binding and signaling has important implications for TCR and antigen engineering for immunotherapy.

Phosphatidylinositol-4-kinase IIα licenses phagosomes for TLR4 signaling and MHC-II presentation in dendritic cells.

Toll-like receptor (TLR) recruitment to phagosomes in dendritic cells (DCs) and downstream TLR signaling are essential to initiate antimicrobial immune responses. However, the mechanisms underlying TLR localization to phagosomes are poorly characterized. We show herein that phosphatidylinositol-4-kinase IIα (PI4KIIα) plays a key role in initiating phagosomal TLR4 responses in murine DCs by generating a phosphatidylinositol-4-phosphate (PtdIns4P) platform conducive to the binding of the TLR sorting adaptor Toll-IL1 receptor (TIR) domain-containing adaptor protein (TIRAP). PI4KIIα is recruited to maturing lipopolysaccharide (LPS)-containing phagosomes in an adaptor protein-3 (AP-3)-dependent manner, and both PI4KIIα and PtdIns4P are detected on phagosomal membrane tubules. Knockdown of PI4KIIα-but not the related PI4KIIß-impairs TIRAP and TLR4 localization to phagosomes, reduces proinflammatory cytokine secretion, abolishes phagosomal tubule formation, and impairs major histocompatibility complex II (MHC-II) presentation. Phagosomal TLR responses in PI4KIIα-deficient DCs are restored by reexpression of wild-type PI4KIIα, but not of variants lacking kinase activity or AP-3 binding. Our data indicate that PI4KIIα is an essential regulator of phagosomal TLR signaling in DCs by ensuring optimal TIRAP recruitment to phagosomes.

Pathogen diversity drives the evolution of generalist MHC-II alleles in human populations.

Central players of the adaptive immune system are the groups of proteins encoded in the major histocompatibility complex (MHC), which shape the immune response against pathogens and tolerance to self-peptides. The corresponding genomic region is of particular interest, as it harbors more disease associations than any other region in the human genome, including associations with infectious diseases, autoimmune disorders, cancers, and neuropsychiatric diseases. Certain MHC molecules can bind to a much wider range of epitopes than others, but the functional implication of such an elevated epitope-binding repertoire has remained largely unclear. It has been suggested that by recognizing more peptide segments, such promiscuous MHC molecules promote immune response against a broader range of pathogens. If so, the geographical distribution of MHC promiscuity level should be shaped by pathogen diversity. Three lines of evidence support the hypothesis. First, we found that in pathogen-rich geographical regions, humans are more likely to carry highly promiscuous MHC class II DRB1 alleles. Second, the switch between specialist and generalist antigen presentation has occurred repeatedly and in a rapid manner during human evolution. Third, molecular positions that define promiscuity level of MHC class II molecules are especially diverse and are under positive selection in human populations. Taken together, our work indicates that pathogen load maintains generalist adaptive immune recognition, with implications for medical genetics and epidemiology.

Structure of MHC-Independent TCRs and Their Recognition of Native Antigen CD155.

During normal T cell development in the thymus, αß TCRs signal immature thymocytes to differentiate into mature T cells by binding to peptide-MHC ligands together with CD4/CD8 coreceptors. Conversely, in MHC and CD4/CD8 coreceptor-deficient mice, the thymus generates mature T cells expressing MHC-independent TCRs that recognize native conformational epitopes rather than linear antigenic-peptides presented by MHC. To date, no structural information of MHC-independent TCRs is available, and their structural recognition of non-MHC ligand remains unknown. To our knowledge in this study, we determined the first structures of two murine MHC-independent TCRs (A11 and B12A) that bind with high nanomolar affinities to mouse adhesion receptor CD155. Solution binding demonstrated the Vαß-domain is responsible for MHC-independent B12A recognition of its ligand. Analysis of A11 and B12A sequences against various MHC-restricted and -independent TCR sequence repertoires showed that individual V-genes of A11 and B12A did not exhibit preference against MHC-restriction. Likewise, CDR3 alone did not discriminate against MHC binding, suggesting VDJ recombination together with Vα/Vß pairing determine their MHC-independent specificity for CD155. The structures of A11 and B12A TCR are nearly identical to those of MHC-restricted TCR, including the conformations of CDR1 and 2. Mutational analysis, together with negative-staining electron microscopy images, showed that the CDR regions of A11 and B12A recognized epitopes on D1 domain of CD155, a region also involved in CD155 binding to poliovirus and Tactile in human. Taken together, MHC-independent TCRs adopt canonical TCR structures to recognize native Ags, highlighting the importance of thymic selection in determining TCR ligand specificity.

Facial masculinity does not appear to be a condition-dependent male ornament and does not reflect MHC heterozygosity in humans.

Recent studies have called into question the idea that facial masculinity is a condition-dependent male ornament that indicates immunocompetence in humans. We add to this growing body of research by calculating an objective measure of facial masculinity/femininity using 3D images in a large sample (n = 1,233) of people of European ancestry. We show that facial masculinity is positively correlated with adult height in both males and females. However, facial masculinity scales with growth similarly in males and females, suggesting that facial masculinity is not exclusively a male ornament, as male ornaments are typically more sensitive to growth in males compared with females. Additionally, we measured immunocompetence via heterozygosity at the major histocompatibility complex (MHC), a widely-used genetic marker of immunity. We show that, while height is positively correlated with MHC heterozygosity, facial masculinity is not. Thus, facial masculinity does not reflect immunocompetence measured by MHC heterozygosity in humans. Overall, we find no support for the idea that facial masculinity is a condition-dependent male ornament that has evolved to indicate immunocompetence.

LANA and hnRNP A1 Regulate the Translation of LANA mRNA through G-Quadruplexes.

During the latent phase, Kaposi's sarcoma-associated herpes virus (KSHV) maintains itself inside the host by escaping the host immune surveillance mechanism through restricted protein expression. Latency-associated nuclear antigen (LANA), the most abundantly expressed protein, is essential for viral persistence, as it plays important roles in latent viral DNA replication and efficient segregation of the viral genome to the daughter cells following cell division. KSHV evades immune detection by maintaining the levels of LANA protein below a threshold required for detection by the host immune system but sufficient to maintain the viral genome. LANA achieves this by controlling its expression through regulation of its promoters and by inhibiting its presentation through interaction with the proteins of class I and class II major histocompatibility complex (MHC) pathways. In this study, we identified a mechanism of LANA expression and restricted immune recognition through formation of G-quadruplexes in LANA mRNA. We show that the formation of these stable structures in LANA mRNA inhibits its translation to control antigen presentation, which was supported by treatment of cells with TMPyP4, a G-quadruplex-stabilizing ligand. We identified heterogenous ribonucleoprotein A1 (hnRNP A1) as a G-quadruplex-unwinding helicase, which unfolds these stable secondary structures to regulate LANA translation.IMPORTANCE LANA, the most abundantly expressed protein during latency, is a multifunctional protein which is absolutely required for the persistence of KSHV in the host cell. Even though the functions of LANA in aiding pathogenesis of the virus have been extensively studied, the mechanism of how LANA escapes host's immune surveillance is not fully understood. This study sheds light on the autoregulatory role of LANA to modulate its expression and immune evasion through formation of G-quadruplexes in its mRNA. We used G-quadruplex-stabilizing ligand to define the inhibition in LANA expression and presentation on the cell surface through MHC class I. We defined the autoregulatory role of LANA and identified a cellular RNA helicase, hnRNP A1, regulating the translation of LANA mRNA. This interaction of hnRNP A1 with LANA mRNA could be exploited for controlling KSHV latency.

An Engineered T Cell Receptor Variant Realizes the Limits of Functional Binding Modes.

T cell receptors (TCRs) orchestrate cellular immunity by recognizing peptides presented by a range of major histocompatibility complex (MHC) proteins. Naturally occurring TCRs bind the composite peptide/MHC surface, recognizing peptides that are structurally and chemically compatible with the TCR binding site. Here we describe a molecularly evolved TCR variant that binds the human class I MHC protein HLA-A2 independent of the bound peptide, achieved by a drastic perturbation of the TCR binding geometry that places the molecule far from the peptide binding groove. This unique geometry is unsupportive of normal T cell signaling. A substantial divergence between affinity measurements in solution and in two dimensions between proximal cell membranes leads us to attribute the lack of signaling to steric hindrance that limits binding in the confines of a cell-cell interface. Our results provide an example of how receptor binding geometry can impact T cell function and provide further support for the view that germline-encoded residues in TCR binding loops evolved to drive productive TCR recognition and signaling.

Nomenclature report 2019: major histocompatibility complex genes and alleles of Great and Small Ape and Old and New World monkey species.

The major histocompatibility complex (MHC) is central to the innate and adaptive immune responses of jawed vertebrates. Characteristic of the MHC are high gene density, gene copy number variation, and allelic polymorphism. Because apes and monkeys are the closest living relatives of humans, the MHCs of these non-human primates (NHP) are studied in depth in the context of evolution, biomedicine, and conservation biology. The Immuno Polymorphism Database (IPD)-MHC NHP Database (IPD-MHC NHP), which curates MHC data of great and small apes, as well as Old and New World monkeys, has been upgraded. The curators of the database are responsible for providing official designations for newly discovered alleles. This nomenclature report updates the 2012 report, and summarizes important nomenclature issues and relevant novel features of the IPD-MHC NHP Database.

Marriage does not relate to major histocompatibility complex: a genetic analysis based on 3691 couples.

Optimization of chances for healthy offspring is thought to be one of the factors driving mate choice and compatibility of the major histocompatibility complex (MHC) is assumed to determine the offspring's fitness. While humans have been claimed to be able to perceive information of MHC compatibility via the olfactory channel, it remains unknown whether humans use such information for mate choice. By investigation of 3691 married couples, we observed that the high polymorphism of MHC leads to a low chance for homozygous offspring. MHC similarity between couples did not differ from chance, we hence observed no MHC effect in married couples. Hormonal contraception at the time of relationship initiation had no significant effect towards enhanced similarity. A low variety of alleles within a postcode area led to a higher likelihood of homozygous offspring. Based on this data, we conclude that there is no pattern of MHC dis-assortative mating in a genetically diverse Western society. We discuss the question of olfactory mate preference, in-group mating bias and the high polymorphism as potential explanations.

NMR-directed design of pre-TCRß and pMHC molecules implies a distinct geometry for pre-TCR relative to αßTCR recognition of pMHC.

The pre-T cell receptor (pre-TCR) guides early thymocytes through maturation processes within the thymus via interaction with self-ligands displayed on thymic epithelial cells. The pre-TCR is a disulfide-linked heterodimer composed of an invariant pre-TCR α (pTα) subunit and a variable ß subunit, the latter of which is incorporated into the mature TCR in subsequent developmental progression. This interaction of pre-TCR with peptide-major histocompatibility complex (pMHC) molecules has recently been shown to drive robust pre-TCR signaling and thymocyte maturation. Although the native sequences of ß are properly folded and suitable for NMR studies in isolation, a tendency to self-associate rendered binding studies with physiological ligands difficult to interpret. Consequently, to structurally define this critical interaction, we have re-engineered the extracellular regions of ß, designated as ß-c1, for prokaryotic production to be used in NMR spectroscopy. Given the large size of the full extracellular domain of class I MHC molecules such as H-Kb, we produced a truncated form termed Kb-t harboring properties favorable for NMR measurements. This system has enabled robust measurement of a pre-TCR-pMHC interaction directly analogous to that of TCRαß-pMHC. Binding surface analysis identified a contact surface comparable in size to that of the TCRαß-pMHC but potentially with a rather distinct binding orientation. A tilting of the pre-TCRß when bound to the pMHC ligand recognition surface versus the upright orientation of TCRαß would alter the direction of force application between pre-TCR and TCR mechanosensors, impacting signal initiation.

Phenotypic variations in transferred progeny due to genotype of surrogate mother.

STUDY QUESTION: Does the genotype of the surrogate mother modulate the body composition and immunity of her offspring? SUMMARY ANSWER: C57BL/6J (B6) progenies carried by immunodeficient NOD SCID (NS) mothers had increased adaptive but decreased innate, immune responsiveness in comparison with the same genotype offspring carried by immunocompetent mothers, B6 and BALB/c (C); the B6 progenies carried by the same genotype mothers also showed higher body fat than the others. WHAT IS KNOWN ALREADY: Differences in the major histocompatibility complex (MHC) genes between mother and foetus is considered as an important factor in prenatal embryo development, whereas the impact of such dissimilarity on the phenotype of the mature progeny is unclear. STUDY DESIGN, SIZE, DURATION: Transplantation of two-cell mouse embryos into recipient females of the different MHC (H2) genotypes was used as an approach to simulate three variants of the immunogenic mother-foetus interaction: (i) bidirectional immunogenic dialogue between B6 (H2b haplotype) embryos and C (H2d haplotype) surrogate mother; (ii) one-way immunogenic interaction between B6 embryos and immunodeficient NS (H2g7 haplotype) surrogate mother and (iii) reduced immunogenetic dialogue between embryos and surrogate mother of the same H2b haplotype resulting in only a maternal response to HY antigens of male foetuses. Delivered by Caesarean section, pups were fostered by lactating B6 females and weighed after weaning (n = 171). Body mass and composition and innate and adaptive immunity were assessed in selected progeny groups at 9-11 weeks of age. PARTICIPANTS/MATERIALS, SETTING, METHODS: The study was performed on the specific pathogen-free mouse, inbred strains C57BL/6J, NOD SCID and BALB/c. Plasma progesterone in pregnant females was measured by enzyme-linked immunosorbent assay (ELISA). Body composition was determined by magnetic resonance spectroscopy using a low-field NMR spectrometer (EchoMRI, USA). To assess peritoneal macrophage responses (innate immunity) to anthrax, lactate dehydrogenase (LDH) and interleukin-1 (IL-1ß) were measured in a culture medium 24 h after the addition of both anthrax-lethal factor and anthrax-protective antigen. To assess adaptive immunity, 9-10 males in experimental groups were infected with Helicobacter hepaticus. Faeces collected 2 and 4 weeks after infection was used for quantitative assessment of the H. hepaticus DNA by real-time polymerase chain reaction. IgA, interferon (IFN-γ), tumour necrosis factor (TNFα), interleukin-17 (IL-17) and interleukin-10 (IL-10) in colon tissue and IgG in serum were determined in samples collected 4 weeks after gavage with H. hepaticus using ELISA. For statistical analyses, ANCOVA, post hoc least significant difference (LSD) test, Student's t-test, Spearman rank correlations and χ2 test were performed. P-value <0.05 was considered as a statistically significant difference. MAIN RESULTS AND THE ROLE OF CHANCE: ANCOVA with litter size and age as covariates revealed significant effects of the surrogate mother genotype on body mass and percent of fat in their adult progeny (F2149 = 15.60, P < 0.001 and F2149 = 5.02, P = 0.007, respectively). Adult B6 mice carried by B6 surrogate mothers were characterized by a higher percentage of body fat in comparison with offspring that were carried by NS and C females. In comparison with the male offspring carried by the B6 and C mothers, male B6 progenies carried by immunodeficient NS mothers had a higher humoral immune response (serum IgG) against oral infection with H. hepaticus, but lower in vitro macrophage IL-1ß reaction to the anthrax. Four weeks after the infection of offspring, concentrations of serum IgG and colon IL-10 correlated positively with maternal progesterone on Day 4 after embryo transfer and negatively with DNA of H. hepaticus. One-way ANOVA confirmed a statistically significant impact of surrogate mother genotype on adaptive (IgG) and innate (IL-1ß) immunity (F2.26 = 26.39, P < 0.001 and F2.27 = 5.89, P = 0.008, respectively). LARGE SCALE DATA: N/A. LIMITATIONS, REASONS FOR CAUTION: The main limitation of our study is the number of combinations of mother and foetus interactions, in particular, transfer of only one embryo genotype was used. Also, it is a descriptive study, which requires further analysis of the epigenetic mechanisms of the observed phenotypic effects of surrogate mother genotype. WIDER IMPLICATIONS OF THE FINDINGS: Our experimental data demonstrate that the transfer of inbred embryos to surrogate mothers of the different genotypes is a prospective experimental model for the study of epigenetic effects of the immunogenetic interactions between mother and foetus. The experimental approach tested in our study will be in demand for the development of criteria for choosing surrogate mothers. In particular, immunocompetence of the surrogate mother along with genetic distance of her MHC alleles to the transferred embryos have a significant impact on offspring development. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the Russian FPI (6/099/2017), budget projects (0324-2016-0002 and 0324-2018-0016) and implemented using the equipment of the Centre for Genetic Resources of Laboratory Animals at ICG SB RAS, supported by the Ministry of Education and Science of Russia (Unique project identifier RFMEFI62117X0015). The authors report no conflicts of interest.

Plumage microbiota covaries with the major histocompatibility complex in blue petrels.

To increase fitness, a wide range of vertebrates preferentially mate with partners that are dissimilar at the major histocompatibility complex (MHC) or that have high MHC diversity. Although MHC often can be assessed through olfactory cues, the mechanism by which MHC genes influence odour remains largely unclear. MHC class IIB molecules, which enable recognition and elimination of extracellular bacteria, have been suggested to influence odour indirectly by shaping odour-producing microbiota, i.e. bacterial communities. However, there is little evidence of the predicted covariation between an animal's MHC genotype and its bacterial communities in scent-producing body surfaces. Here, using high-throughput sequencing, we tested the covariation between MHC class IIB genotypes and feather microbiota in the blue petrel (Halobaena caerulea), a seabird with highly developed olfaction that has been suggested to rely on oduor cues during an MHC-based mate choice. First, we show that individuals with similar MHC class IIB profiles also have similar bacterial assemblages in their feathers. Then, we show that individuals with high MHC diversity have less diverse feather microbiota and also a reduced abundance of a bacterium of the genus Arsenophonus, a genus in which some species are symbionts of avian ectoparasites. Our results, showing that feather microbiota covary with MHC, are consistent with the hypothesis that individual MHC genotype may shape the semiochemical-producing microbiota in birds.

In vitro cellular responses to Neospora caninum glycosylphosphatidylinositols depend on the host origin of antigen presenting cells.

Neosporosis due to Neospora caninum causes abortions in farm animals such as cattle. No treatment and vaccine exist to fight this disease, responsible for considerable economic losses. It is thus important to better understand the immune responses occurring during the pathogenesis to control them in a global strategy against the parasite. In this context, we studied the roles of N. caninum glycosylphosphatidylinositols (GPIs), glycolipids defined as toxins in the related parasite Plasmodium falciparum. We demonstrated for the first time that GPIs could be excreted in the supernatant of N. caninum culture and trigger cell signalling through the Toll-like receptors 2 and 4. In addition, antibodies specific to N. caninum GPIs were detected in the serum of infected mice. As shown for other protozoan diseases, they could play a role in neutralizing GPIs. N. caninum GPIs were able to induce the production of tumour necrosis factor-α, interleukin(IL)-1ß and IL-12 cytokines by murine macrophages and dendritic cells. Furthermore, GPIs significantly reduced expression of major histocompatibility complex (MHC) molecules of class I on murine dendritic cells. In contrast to murine cells, bovine blood mononuclear cells produced increased levels of IFN-γ and IL-10, but reduced levels of IL-12p40 in response to GPIs. On these bovine cells, GPI had the tendency to up-regulate MHC class I, but to down-regulate MHC class II. Altogether, these results suggest that N. caninum GPIs might differentially participate in the responses of antigen presenting cells induced by the whole parasite in mouse models of neosporosis and in the natural cattle host.

Codification of bidentate pMHC interaction with TCR and its co-receptor.

A 1983 Immunology Today rostrum hypothesized that each T cell has two recognition units: a T cell receptor (TCR) complex, which binds antigen associated with a polymorphic region of a MHC molecule (pMHC), and a CD4 or CD8 molecule that binds to a conserved region of that same MHC gene product (class II or I, respectively). Structural biology has since precisely revealed those bidentate pMHC interactions. TCRαß ligates the membrane-distal antigen-binding MHC platform, whereas CD8 clamps a membrane-proximal MHCI α3 domain loop and CD4 docks to a hydrophobic crevice between MHCII α2 and ß2 domains. Here, we review how MHC class-restricted binding impacts signaling and lineage commitment, discussing TCR force-driven conformational transitions that may optimally expose the co-receptor docking site on MHC.

Modeling T-cell acute lymphoblastic leukemia induced by the SCL and LMO1 oncogenes.

Deciphering molecular events required for full transformation of normal cells into cancer cells remains a challenge. In T-cell acute lymphoblastic leukemia (T-ALL), the genes encoding the TAL1/SCL and LMO1/2 transcription factors are recurring targets of chromosomal translocations, whereas NOTCH1 is activated in >50% of samples. Here we show that the SCL and LMO1 oncogenes collaborate to expand primitive thymocyte progenitors and inhibit later stages of differentiation. Together with pre-T-cell antigen receptor (pre-TCR) signaling, these oncogenes provide a favorable context for the acquisition of activating Notch1 mutations and the emergence of self-renewing leukemia-initiating cells in T-ALL. All tumor cells harness identical and specific Notch1 mutations and Tcrbeta clonal signature, indicative of clonal dominance and concurring with the observation that Notch1 gain of function confers a selective advantage to SCL-LMO1 transgenic thymocytes. Accordingly, a hyperactive Notch1 allele accelerates leukemia onset induced by SCL-LMO1 and bypasses the requirement for pre-TCR signaling. Finally, the time to leukemia induced by the three transgenes corresponds to the time required for clonal expansion from a single leukemic stem cell, suggesting that SCL, LMO1, and Notch1 gain of function, together with an active pre-TCR, might represent the minimum set of complementing events for the transformation of susceptible thymocytes.

Individual Differences of Multipotent Mesenchymal Stromal Cells Manifesting in during Interaction with Lymphocytes.

Analysis of changes in lymphocyte subpopulations during co-culturing with multipotent mesenchymal stromal cells (MSC) revealed two distinct MSC groups: one group (A) increased HLA-DR expression on lymphocytes during co-culturing and the other (B) did not change it in comparison with lymphocyte monoculture. In stromal cells interacting with lymphocytes, expression of HLA-DR molecules was initiated, but only in samples that induced enhanced expression on lymphocytes and irrespectively of whether allogeneic or autologous lymphocytes were used for co-culturing with MSC. In group A, the relative expression of IDO1 significantly increased in comparison with group B. The revealed individual differences in MSC can explain why not all MSC samples are effective in the treatment of autoimmune diseases, acute "graft-versus-host" disease, and other pathologies.

Thioredoxin (Trx1) regulates CD4 membrane domain localization and is required for efficient CD4-dependent HIV-1 entry.

BACKGROUND: CD4 is a glycoprotein expressed on the surfaces of certain immune cells. On lymphocytes, an important function of CD4 is to co-engage Major Histocompatibility Complex (MHC) molecules with the T Cell Receptor (TCR), a process that is essential for antigen-specific activation of T cells. CD4 localizes dynamically into distinct membrane microdomains, an important feature of its immunoregulatory function that has also been shown to influence the efficiency of HIV replication. However, the mechanism by which CD4 localization is regulated and the biological significance of this is incompletely understood. METHODS: In this study, we used confocal microscopy, density-gradient centrifugation and flow cytometry to analyze dynamic redox-dependent effects on CD4 membrane domain localization. RESULTS: Blocking cell surface redox exchanges with both a membrane-impermeable sulfhydryl blocker (DTNB) and specific antibody inhibitors of Thioredoxin-1 (Trx1) induces translocation of CD4 into detergent-resistant membrane domains (DRM). In contrast, Trx1 inactivation does not change the localization of the chemokine receptor CCR5, suggesting that this effect is targeted. Moreover, DTNB treatment and Trx1 depletion coincide with strong inhibition of CD4-dependent HIV entry, but only moderate reductions in the infectivity of a CD4-independent HIV pseudovirion. CONCLUSIONS: Changes in the extracellular redox environment, potentially mediated by allosteric consequences of functional disulfide bond oxidoreduction, may represent a signal for translocation of CD4 into DRM clusters, and this sequestration, another potential mechanism by which the anti-HIV effects of cell surface oxidoreductase inhibition are exerted. GENERAL SIGNIFICANCE: Extracellular redox conditions may regulate CD4 function by potentiating changes in its membrane domain localization.

MHC and adaptive immunity in teleost fishes.

The adaptive immune system has long been considered a key evolutionary innovation of the vertebrates, the product of two rounds of genome duplication that gave rise to the raw material necessary for the evolution of a highly specific immune response and immune memory. While comparative studies of a small number of model organisms have led to the commonly held view that the adaptive immune system has remained relatively static since its origin, recent studies of non-model organisms are challenging this notion, highlighting the fact that we have only begun to scratch the surface in terms of our understanding of immune system diversity. Some of the most exciting recent results have come from the comparative analysis of teleost fishes, a group that includes more than 40% of vertebrates, and shows remarkable diversity in immune system structure and function. Despite the repeated loss of key components of the adaptive immune machinery in this group, affected species are capable of mounting a robust response to immune challenge, suggesting that they have evolved alternative mechanisms of immune protection. Such deviations from the canonical model of vertebrate immunity create opportunities to explore common paradigms of immune function, and may contribute to new experimental approaches and methods of treatment.

Testing mate choice and overdominance at MH in natural families of Atlantic salmon Salmo salar.

This study aimed to test mate choice and selection during early life stages on major histocompatibility (MH) genotype in natural families of Atlantic salmon Salmo salar spawners and juveniles, using nine microsatellites to reconstruct families, one microsatellite linked to an MH class I gene and one minisatellite linked to an MH class II gene. MH-based mate choice was only detected for the class I locus on the first year, with lower expected heterozygosity in the offspring of actually mated pairs than predicted under random mating. The genotype frequencies of MH-linked loci observed in the juveniles were compared with frequencies expected from Mendelian inheritance of parental alleles to detect selection during early life stages. No selection was detected on the locus linked to class I gene. For the locus linked to class II gene, observed heterozygosity was higher than expected in the first year and lower in the second year, suggesting overdominance and underdominance, respectively. Within family, juveniles' body size was linked to heterozygosity at the same locus, with longer heterozygotes in the first year and longer homozygotes in the second year. Selection therefore seems to differ from one locus to the other and from year to year.

Changing the Properties of Multipotent Mesenchymal Stromal Cells by IFNγ Administration.

We studied changes in the population of human multipotent mesenchymal stromal cells activated by IFNγ. The cells were cultured under standard conditions; IFNγ was added in various concentrations for 4 h or over 2 passages. It was shown that the total cell production significantly decreased after long-term culturing with IFNγ, but 4-h exposure did not affect this parameter. After 4-h culturing, the expression levels of IDO1, CSF1, and IL-6 increased by 300, 7, and 2.4 times, respectively, and this increase persisted 1 and 2 days after removal of IFNγ from the culture medium. The expression of class I and II MHC (HLA) on cell surface practically did not change immediately after exposure to IFNγ, but during further culturing, HLA-ABC (MHC I) and HLA-DR (MHC II) expression significantly increased, which abolished the immune privilege in these cells, the property allowing clinical use of allogenic multipotent mesenchymal stromal cells. Multipotent mesenchymal stromal cells can suppress proliferation of lymphocytes. The degree of this suppression depends on individual properties of multipotent mesenchymal stromal cell donor. Treatment with IFNγ did not significantly affect the intensity of inhibition of lymphocyte proliferation by these cells.