Open MHC Class I Conformers: A Look through the Looking Glass

IL-10 and TGF-β, but Not IL-17A or IFN-γ, Potentiate the IL-15-Induced Proliferation of Human T Cells: Association with a Decrease in the Expression of β2m-Free HLA Class I Molecules Induced by IL-15

IL-15 is a homeostatic cytokine for human T and NK cells. However, whether other cytokines influence the effect of IL-15 is not known. We studied the impact that IL-10, TGF-β, IL-17A, and IFN-γ have on the IL-15-induced proliferation of human T cells and the expression of HLA class I (HLA-I) molecules. Peripheral blood lymphocytes (PBLs) were labeled with CFSE and stimulated for 12 days with IL-15 in the absence or presence of the other cytokines. The proportion of proliferating T cells and the expression of cell surface HLA-I molecules were analyzed using flow cytometry. The IL-15-induced proliferation of T cells was paralleled by an increase in the expression of HC-10-reactive HLA-I molecules, namely on T cells that underwent ≥5-6 cycles of cell division. It is noteworthy that the IL-15-induced proliferation of T cells was potentiated by IL-10 and TGF-β but not by IL-17 or IFN-γ and was associated with a decrease in the expression of HC-10-reactive molecules. The cytokines IL-10 and TGF-β potentiate the proliferative capacity that IL-15 has on human T cells in vitro, an effect that is associated with a reduction in the amount of HC-10 reactive HLA class I molecules induced by IL-15.

In vitro IL-15-activated human naïve CD8+ T cells down-modulate the CD8β chain and become CD8αα T cells

Antigen-driven human effector-memory CD8+ T cells expressing low levels of the CD8β chain have been previously described. However, little is known on a possible antigen-independent trigger. We have examined the impact that IL-15 has on the expression of CD8β on purified human naïve CD8+ T cells after CFSE labeling and culture with IL-15. As expected, IL-15 induced naïve CD8+ T cells to proliferate and differentiate. Remarkably, the process was associated with a cell-cycle dependent down-modulation of CD8β from the cell surface, leading to the generation of CD8αβlow and CD8αβ- (i.e., CD8αα) T cells. In contrast, expression of the CD8α chain remained steady or even increased. Neither IL-2 nor IL-7 reproduced the effect of IL-15. Determination of mRNA levels for CD8α and CD8β isoforms by qPCR revealed that IL-15 promoted a significant decrease in mRNA levels of the CD8β M-4 isoform, while levels of the M-1/M-2 isoforms and of CD8α increased. Noteworthy, CD8+ T cell blasts obtained after culture of CD8+ T cells with IL-15 showed a cell-cycle dependent increase in the level of the tyrosine kinase Lck, when compared to CD8+ T cells at day 0. This study has shown for the first time that IL-15 generates CD8αα+αβlow and CD8αα+αβ- T cells containing high levels of Lck, suggesting that they may be endowed with unique functional features.

HLA-A23/HLA-A24 serotypes and dementia interaction in the elderly: Association with increased soluble HLA class I molecules in plasma

MHC class I molecules regulate brain development and plasticity in mice and HLA class I molecules are associated with brain disorders in humans. We investigated the relationship between plasma-derived soluble human HLA class I molecules (sHLA class I), HLA class I serotypes and dementia. A cohort of HLA class I serotyped elderly subjects with no dementia/pre-dementia (NpD, n = 28), or with dementia (D, n = 28) was studied. Multivariate analysis was used to examine the influence of dementia and HLA class I serotype on sHLA class I levels, and to compare sHLA class I within four groups according to the presence or absence of HLA-A23/A24 and dementia. HLA-A23/A24 and dementia, but not age, significantly influenced the level of sHLA class I. Importantly, the concurrent presence of HLA-A23/A24 and dementia was associated with higher levels of sHLA class I (p < 0.001). This study has shown that the simultaneous presence of HLA-A23/HLA-A24 and dementia is associated with high levels of serum sHLA class I molecules. Thus, sHLA class I could be considered a biomarker of neurodegeneration in certain HLA class I carriers.

Non-Classical HLA Class 1b and Hepatocellular Carcinoma

A number of studies are underway to gain a better understanding of the role of immunity in the pathogenesis of hepatocellular carcinoma and to identify subgroups of individuals who may benefit the most from systemic therapy according to the etiology of their tumor. Human leukocyte antigens play a key role in antigen presentation to T cells. This is fundamental to the host's defense against pathogens and tumor cells. In addition, HLA-specific interactions with innate lymphoid cell receptors, such those present on natural killer cells and innate lymphoid cell type 2, have been shown to be important activators of immune function in the context of several liver diseases. More recent studies have highlighted the key role of members of the non-classical HLA-Ib and the transcript adjacent to the HLA-F locus, FAT10, in hepatocarcinoma. The present review analyzes the major contribution of these molecules to hepatic viral infection and hepatocellular prognosis. Particular attention has been paid to the association of natural killer and Vδ2 T-cell activation, mediated by specific HLA class Ib molecules, with risk assessment and novel treatment strategies to improve immunotherapy in HCC.

Emerging phagocytosis checkpoints in cancer immunotherapy

Cancer immunotherapy, mainly including immune checkpoints-targeted therapy and the adoptive transfer of engineered immune cells, has revolutionized the oncology landscape as it utilizes patients' own immune systems in combating the cancer cells. Cancer cells escape immune surveillance by hijacking the corresponding inhibitory pathways via overexpressing checkpoint genes. Phagocytosis checkpoints, such as CD47, CD24, MHC-I, PD-L1, STC-1 and GD2, have emerged as essential checkpoints for cancer immunotherapy by functioning as "don't eat me" signals or interacting with "eat me" signals to suppress immune responses. Phagocytosis checkpoints link innate immunity and adaptive immunity in cancer immunotherapy. Genetic ablation of these phagocytosis checkpoints, as well as blockade of their signaling pathways, robustly augments phagocytosis and reduces tumor size. Among all phagocytosis checkpoints, CD47 is the most thoroughly studied and has emerged as a rising star among targets for cancer treatment. CD47-targeting antibodies and inhibitors have been investigated in various preclinical and clinical trials. However, anemia and thrombocytopenia appear to be formidable challenges since CD47 is ubiquitously expressed on erythrocytes. Here, we review the reported phagocytosis checkpoints by discussing their mechanisms and functions in cancer immunotherapy, highlight clinical progress in targeting these checkpoints and discuss challenges and potential solutions to smooth the way for combination immunotherapeutic strategies that involve both innate and adaptive immune responses.

Dissociation of β2m from MHC class I Triggers formation of Noncovalent, transient heavy chain dimers

At the plasma membrane of mammalian cells, major histocompatibility complex class I molecules (MHC-I) present antigenic peptides to cytotoxic T cells. Following the loss of the peptide and the light chain beta-2 microglobulin (β2m), the resulting free heavy chains (FHCs) can associate into homotypic complexes in the plasma membrane. Here, we investigate the stoichiometry and dynamics of MHC-I FHCs assemblies by combining a micropattern assay with fluorescence recovery after photobleaching (FRAP) and with single molecule co-tracking. We identify non-covalent MHC-I FHC dimers mediated by the α3 domain as the prevalent species at the plasma membrane, leading a moderate decrease in the diffusion coefficient. MHC-I FHC dimers show increased tendency to cluster into higher order oligomers as concluded from an increased immobile fraction with higher single molecule co-localization. In vitro studies with isolated proteins in conjunction with molecular docking and dynamics simulations suggest that in the complexes, the α3 domain of one FHC binds to another FHC in a manner similar to the β2m light chain.

Ramifications of the HLA-I Allelic Reactivity of Anti-HLA-E*01:01 and Anti-HLA-E*01:03 Heavy Chain Monoclonal Antibodies in Comparison with Anti-HLA-I IgG Reactivity in Non-Alloimmunized Males, Melanoma-Vaccine Recipients, and End-Stage Renal Disease Patients

Serum anti-HLA-I IgG are present in non-alloimmunized males, cancer patients, and transplant recipients. Anti-HLA-I antibodies are also present in intravenous immunoglobulin (IVIg), prepared from the plasma of thousands of healthy donors. However, the HLA-Ia reactivity of IVIg diminishes markedly after passing through HLA-E HC-affinity columns, suggesting that the HLA-I reactivity is due to antibodies formed against HLA-E. Hence, we examined whether anti-HLA-E antibodies can react to HLA-I alleles. Monoclonal IgG antibodies (mAbs) against HCs of two HLA-E alleles were generated in Balb/C mice. The antibodies were analyzed using multiplex bead assays on a Luminex platform for HLA-I reactivity. Beads coated with an array of HLA heterodimers admixed with HCs (LABScreen) were used to examine the binding of IgG to different HLA-Ia (31-HLA-A, 50-HLA-B, and 16-HLA-C) and Ib (2-HLA-E, one each of HLA-F and HLA-G) alleles. A striking diversity in the HLA-Ia and/or HLA-Ib reactivity of mAbs was observed. The number of the mAbs reactive to (1) only HLA-E (n = 25); (2) all HLA-Ib isomers (n = 8); (3) HLA-E and HLA-B (n = 5); (4) HLA-E, HLA-B, and HLA-C (n = 30); (5) HLA-E, HLA-A*1101, HLA-B, and HLA-C (n = 83); (6) HLA-E, HLA-A, HLA-B, and HLA-C (n = 54); and (7) HLA-Ib and HLA-Ia (n = 8), in addition to four other minor groups. Monospecificity and polyreactivity were corroborated by HLA-E monospecific and HLA-I shared sequences. The diverse HLA-I reactivity of the mAbs are compared with the pattern of HLA-I reactivity of serum-IgG in non-alloimmunized males, cancer patients, and ESKD patients. The findings unravel the diagnostic potential of the HLA-E monospecific-mAbs and immunomodulatory potentials of IVIg highly mimicking HLA-I polyreactive-mAbs.

Homotypic and heterotypic in cis associations of MHC class I molecules at the cell surface

Through the presentation of peptide antigens to cytotoxic T lymphocytes, major histocompatibility complex (MHC) class I molecules mediate the adaptive immune response against tumors and viruses. Additional non-immunological functions include the heterotypic association of class I molecules with cell surface receptors, regulating their activities by unknown mechanisms. Also, homotypic associations resulting in class I dimers and oligomers - of unknown function - have been related to pathological outcomes. In this review, we provide an overview of the current knowledge about the occurrence, biochemical nature, and dynamics of homotypic and heterotypic associations of class I molecules at the cell surface with special focus on the molecular species that take part in the complexes and on the evidence that supports novel biological roles for class I molecules. We show that both heterotypic and homotypic class I associations reported in the literature describe not one but several kinds of oligomers with distinctive stoichiometry and biochemical properties.

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Major histocompatibility complex class I molecules form homotypic and heterotypic associations at the cell surface.

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Associations show distinctive stoichiometry and biochemical properties.

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Associations might regulate immunological and non-immunological processes.

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Heterotypic association with cell surface receptors might regulate receptor's activity.

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Homotypic associations have been related to pathological outcomes.

Albinism in the largest extant amphibian: A metabolic, endocrine, or immune problem?

BACKGROUND

Pigment regression is an intriguing phenomenon that can be caused by disorders in melanin metabolism or endocrine regulation, or by autoimmune disorders. Albino animals serve as excellent models for the study of the genetic determination of morphology, particularly the evolution of and molecular mechanisms underlying chromatophore-related diseases in animals and humans.

MATERIAL AND METHODS

The artificial culture of Andrias davidianus, the largest extant amphibian, is flourishing in China due to the great ecological and economic value of this animal. Approximately 0.1% of individuals express an albino phenotype accompanied by delayed somatic growth and mortality at early developmental stages. In this study, brain and skin transcriptomics were conducted to study the underlying molecular basis of the phenotype.

RESULTS

The results indicated decreased transcription of genes of melanin synthesis. Interestingly, MHC I isotypes and immune-related pathways accounted for the primary transcriptional differences between groups, suggesting that the albino phenotype represents a systematic immune problem to a far greater extent than a pigmentation defect. Albino individuals exhibited shifted transcription of MHC I isotypes, and the albino-specific isotype was characterized by increased charges and decreased space in the antigen- binding pocket, implying a drastic change in antigen specificity and a potential risk of autoimmune disorders.

CONCLUSION

These results suggest an association between the albino phenotype and MHC I variants in A. davidianus, which could serve as a convenient model for vitiligo or other autoimmune diseases.

Antibodies to cryptic epitopes on HLA class I and class II heavy chains bound to single antigen beads: Clinically relevant?

Cell surface HLA class I consists of trimers, i.e., alpha - heavy chain, beta - 2 - microglobulin, and a peptide, termed closed conformers (CC) on non-activated lymphocytes. HLA class I and class II may also exist, respectively, as alpha-chain only or alpha and beta - chain only on activated cells termed open conformers (OC). We extend previous studies using an OC-specific monoclonal antibody that demonstrate LABScreen HLA class I and II single antigen beads (SABs) contain a mixture of open and closed conformers. LIFECODES SABs have bound CC only. More HLA class I and class II LABScreen SABs were reactive than LIFECODES SABs due to the presence of OC on LABScreen SABs. We hypothesized that antibody against OC on HLA B antigens would not be detected in cell based cross matches (XMs) with typical lymphocyte targets since anti-HLA OC antibodies would not react with native HLA CC on the cell surface. To test this hypothesis, we performed flow cytometry XM (FCXM) assays with sera of sufficient strength that most laboratories would likely predict positive FCXMs. Sera that reacted strongly with LABScreen SABs (>13,000 MFI) but weakly or not at all with LIFECODES SABs (<1000 MFI) gave negative T and B cell FCXMs. In contrast, sera that reacted with LIFECODES SABs (>13,000 MFI) but weakly with LABScreen SABs (<2100 MFI) exhibited positive FCXMs. Detection of antibodies directed against OC in SAB assays, may lead to inappropriate listing of unacceptable antigens, a decision not to XM or pre-or post - transplant desensitization procedures.