T cell receptor-independent CD4 signalling: CD4-MHC class II interactions regulate intracellular calcium and cyclic AMP

Progression to type 1 diabetes in the DPT-1 and TN07 clinical trials is critically associated with specific residues in HLA-DQA1-B1 heterodimers

AIMS/HYPOTHESIS

The aim of this work was to explore molecular amino acids (AAs) and related structures of HLA-DQA1-DQB1 that underlie its contribution to the progression from stages 1 or 2 to stage 3 type 1 diabetes.

METHODS

Using high-resolution DQA1 and DQB1 genotypes from 1216 participants in the Diabetes Prevention Trial-Type 1 and the Diabetes Prevention Trial, we applied hierarchically organised haplotype association analysis (HOH) to decipher which AAs contributed to the associations of DQ with disease and their structural properties. HOH relied on the Cox regression to quantify the association of DQ with time-to-onset of type 1 diabetes.

RESULTS

By numerating all possible DQ heterodimers of α- and β-chains, we showed that the heterodimerisation increases genetic diversity at the cellular level from 43 empirically observed haplotypes to 186 possible heterodimers. Heterodimerisation turned several neutral haplotypes (DQ2.2, DQ2.3 and DQ4.4) to risk haplotypes (DQ2.2/2.3-DQ4.4 and DQ4.4-DQ2.2). HOH uncovered eight AAs on the α-chain (-16α, -13α, -6α, α22, α23, α44, α72, α157) and six AAs on the β-chain (-18β, β9, β13, β26, β57, β135) that contributed to the association of DQ with progression of type 1 diabetes. The specific AAs concerned the signal peptide (minus sign, possible linkage to expression levels), pockets 1, 4 and 9 in the antigen-binding groove of the α1β1 domain, and the putative homodimerisation of the αβ heterodimers.

CONCLUSIONS/INTERPRETATION

These results unveil the contribution made by DQ to type 1 diabetes progression at individual residues and related protein structures, shedding light on its immunological mechanisms and providing new leads for developing treatment strategies.

DATA AVAILABILITY

Clinical trial data and biospecimen samples are available through the National Institute of Diabetes and Digestive and Kidney Diseases Central Repository portal ( https://repository.niddk.nih.gov/studies ).

Blood signatures for second stage human African trypanosomiasis: a transcriptomic approach

BACKGROUND

Rhodesiense sleeping sickness is caused by infection with T. b rhodesiense parasites resulting in an acute disease that is fatal if not treated in time. The aim of this study was to understand the global impact of active T. b rhodesiense infection on the patient's immune response in the early and late stages of the disease.

METHODS

RNASeq was carried out on blood and cerebral spinal fluid (CSF) samples obtained from T. b. rhodesiense infected patients. The control samples used were from healthy individuals in the same foci. The Illumina sequenced reads were analysed using the Tuxedo suite pipeline (Tophat, Cufflinks, Cuffmerge, Cuffdiff) and differential expression analysis carried out using the R package DESeq2. The gene enrichment and function annotation analysis were done using the ToppCluster, DAVID and InnateDB algorithms.

RESULTS

We previously described the transcriptomes of T. b rhodesiense from infected early stage blood (n = 3) and late stage CSF (n = 3) samples from Eastern Uganda. We here identify human transcripts that were differentially expressed (padj < 0.05) in the early stage blood versus healthy controls (n = 3) and early stage blood versus late stage CSF. Differential expression in infected blood showed an enrichment of innate immune response genes whereas that of the CSF showed enrichment for anti-inflammatory and neuro-degeneration signalling pathways. We also identified genes (C1QC, MARCO, IGHD3-10) that were up-regulated (log₂ FC > 2.5) in both the blood and CSF.

CONCLUSION

The data yields insights into the host's response to T. b rhodesiense parasites in the blood and central nervous system. We identified key pathways and signalling molecules for the predominant innate immune response in the early stage infection; and anti-inflammatory and neuro-degeneration pathways associated with sleep disorders in second stage infection. We further identified potential blood biomarkers that can be used for diagnosis of late stage disease without the need for lumbar puncture.

Type II PtdIns 4-kinase β associates with CD4-p56lck complex and is involved in CD4 receptor signaling

Type II phosphatidylinositol (PtdIns) 4-kinases are involved in the synthesis of PtdIns 4-phosphates and modulate various cell functions like, intracellular signaling, cytoskeletal rearrangements, vesicular trafficking, and pathogen invasion. In CD3 receptor activated T cells, a type II PtdIns 4-kinase β is recruited to CD3 receptor zeta and plays a role in intracellular calcium release and probably in actin cytoskeleton reorganization. T cell receptor mediated activation is supported by CD4 receptor. The role of type II PtdIns 4-kinase β in CD4 receptor-mediated signaling was addressed in the present manuscript. Crosslinking of CD4 receptors with monoclonal antibodies showed an increase in CD4-associated PtdIns 4-kinase activity and requires p56(lck) activity. Biochemical characterization suggests that it belongs to type II PtdIns 4-kinase family. shRNA mediated knockdown of type II PtdIns 4-kinase β showed abrogation of CD4 receptor induced intracellular calcium release. These results suggest that type II PtdIns 4-kinase β plays an integral part in CD4 receptor-mediated signaling.

Boosting regulatory T cell function by CD4 stimulation enters the clinic

Understanding tolerance mechanisms at the cellular and molecular level holds the promise to establish novel immune intervention therapies in patients with allergy or autoimmunity and to prevent transplant rejection. Administration of mAb against the CD4 molecule has been found to be exceptionally well suited for intentional tolerance induction in rodent and non-human primate models as well as in humanized mouse models. Recent evidence demonstrated that regulatory T cells (Treg) are directly activated by non-depleting CD4 ligands and suggests Treg activation as a central mechanism in anti-CD4-mediated tolerance induction. This review summarizes the current knowledge on the role of Treg in peripheral tolerance, addresses the putative mechanisms of Treg-mediated suppression and discusses the clinical potential of harnessing Treg suppressive activity through CD4 stimulation.

One protein to rule them all: modulation of cell surface receptors and molecules by HIV Nef

The HIV-1, HIV-2 and SIV Nef protein are known to modulate the expression of several cell surface receptors and molecules to escape the immune system, to alter T cell activation, to enhance viral replication, infectivity and transmission and overall to ensure the optimal environment for infection outcome. Consistent and continuous efforts have been made over the years to characterize the modulation of expression of each of these molecules, in the hope that a better understanding of these processes essential for HIV infection and/or pathogenesis will eventually highlight new therapeutic targets. In this article we provide an extensive review of the knowledge gained so far on this important and evolving topic.

J-LEAPS peptide and LEAPS dendritic cell vaccines

The J‐LEAPS vaccines contain a peptide from β‐2‐microglobulin covalently attached to disease‐related peptides of 8–30 amino acids which contain a T cell epitope. The J‐LEAPS vaccines can initiate a protective Th1 immune response or modulate an ongoing Th17 autoimmune response to the peptide. J‐LEAPS vaccines activate and direct the nature of the subsequent immune response by promoting the maturation of precursor cells into a unique type of dendritic cell that produces interleukin 12, but not IL‐1 or tumour necrosis factor, and presents the antigenic peptide to T cells. Adoptive transfer of JgD‐LEAPS dendritic cells, matured with an anti‐HSV‐1 vaccine, promoted antigen‐specific Th1 protection against lethal challenge with the virus. J‐LEAPS peptide immunogens and J‐LEAPS dendritic cell vaccines have potential applications for antimicrobial prevention and therapy, treatment of autoimmune diseases, and for cancer immunotherapy.

Much ado about adenosine: adenosine synthesis and function in regulatory T cell biology

Recent studies have reported that adenosine is a significant mediator of regulatory T cell (Treg) function. Indeed, activation of the adenosine receptor subtypes expressed by a broad range of immune and inflammatory cells attenuates inflammation in several disease models. This anti-inflammatory response is associated with an increase in intracellular cAMP that inhibits cytokine responses of many immune/inflammatory cells, including T cells and APCs. Thus, adenosine produced by Tregs can provide a paracrine feedback that shapes the host response following an immunologic provocation. This review discusses the evidence that adenosine is an integral part of Treg biology and presents some of the mechanisms that may account for its contribution to the resolution of inflammation and the regulation of the immune/inflammatory cell phenotype.

CD4 engagement by CD1d potentiates activation of CD4+ invariant NKT cells

The CD4 coreceptor is crucial in the activation of major histocompatibility complex (MHC) class II restricted CD4 (+) T lymphocytes by binding the same MHC class as the T-cell receptor (TCR) and by potentiating TCR-dependent signaling. CD4 is also expressed by invariant natural killer T cells (iNKT), which recognize natural and synthetic lipid antigens, such as alpha-galactosyl ceramide (alpha-GalCer), in association with the MHC class I-like CD1d molecule. Human iNKT cells can be divided into 2 major subsets depending on CD4 expression: CD4 (+) iNKT preferentially produce T-helper (Th)0/Th2 cytokines, whereas CD4(-) iNKT cells produce Th1 cytokines after antigenic activation. Cytokines produced by iNKT may have immunomodulatory roles in various physiopathologic contexts, but their mode of regulation by iNKT cells remains ill-defined. Using blocking reagents neutralizing CD4 binding, experimental systems where MHC class II molecules are absent and recombinant alpha-GalCer/CD1d complexes, we show that CD4 potentiates human iNKT cell activation by engaging CD1d molecules. These results indicate that the CD4 coreceptors may contribute to the fine tuning of iNKT cells reactivity.

T cell receptor induced intracellular redistribution of type I protein kinase A

The productive activation of CD4(+) T lymphocytes, leading to proliferation and cytokine secretion, requires precise temporal regulation of intracellular cyclic AMP concentrations. The major effector molecule activated by cyclic AMP in mammalian cells is the cyclic AMP-dependent protein kinase A (PKA). The type I PKA isozyme mediates the inhibitory effects of cyclic AMP on T-cell activation. Using laser scanning confocal microscopy, we demonstrated that the regulation of PKA type I activity involves spatial redistribution of PKA type I molecules following T-cell receptor (TCR) stimulation. In resting T cells, PKA type I was located in membrane proximal regions and distributed equally across the cell. Shortly after antigen engagement, T cells and antigen-presenting cells formed an area of intense contact, known as the immunological synapse. TCR concentrated at the synapse, whereas PKA type I molecules redistributed to the opposite cell pole within 10 min after T-cell stimulation. Type I PKA redistribution was solely dependent on TCR signalling, because we observed the same temporal and spatial distribution after antibody-mediated cross-linking of the TCR-associated CD3 complex. Segregation of TCR and PKA type I molecules was maintained for at least 20 min. Thirty minutes after stimulation, PKA type I partially colocalized with the TCR. After 60 min, PKA type I distribution again approached the resting state. Considering that initial TCR signals lead to increases in intracellular cyclic AMP, PKA type I molecules may be targeted towards localized cyclic AMP accumulations or transported away from these areas, depending on the requirements of the cellular response.