Self-Peptidome Variation Shapes Individual Immune Responses.

The relationship between human genetic variation and disease has not been fully elucidated. According to the present view on infectious diseases pathogen resistance is linked to human leukocyte antigen (HLA) class I/II variants and their individual capacity to present pathogen-derived peptides. Yet, T cell education in the thymus occurs through negative and positive selection, and both processes are controlled by a combination of HLA class I/II variants and peptides from the self. Therefore, the capacity of given HLA class I/II variants to bind pathogen-derived peptides is only one part of the selective process to generate effective immune responses. We thus propose that peptidome variation contributes to shaping T cell receptor (TCR) repertoires and hence individual immune responses, and that this variation represents inherent modulator epitopes.

Regulation of a late phase of T cell polarity and effector functions by Crtam.

Spatial organization of cellular proteins plays an important role in establishment of cellular polarity to regulate cell division, differentiation, migration, and organogenesis. Activation of T cells by antigen-presenting cells (APCs) results in the formation of an immunological synapse (IS), assembly of a signaling scaffold at the T cell receptor (TCR) contact, cytoskeletal reorganization, and generation of second messengers within the first hours following intercellular contact. We demonstrate here that Crtam (class-I MHC-restricted T-cell associated molecule), an immunoglobulin-superfamily transmembrane protein, coordinates a signaling complex anchored by the Scrib polarity protein to establish a later phase of T cell polarity on a subset of CD4+ T cells >6 hours following activation. Maintenance of this late cellular polarity results in the ability of CD4+Crtam+ T cells to selectively produce more IFNgamma and IL22. Crtam engagement thus modulates signals many hours beyond the initial activation event and dynamically influences the adaptive immune response.

A model for harmonizing flow cytometry in clinical trials.

Complexities in sample handling, instrument setup and data analysis are barriers to the effective use of flow cytometry to monitor immunological parameters in clinical trials. The novel use of a central laboratory may help mitigate these issues.

Dusp5 negatively regulates IL-33-mediated eosinophil survival and function.

Mitogen-activated protein kinase (MAPK) activation controls diverse cellular functions including cellular survival, proliferation, and apoptosis. Tuning of MAPK activation is counter-regulated by a family of dual-specificity phosphatases (DUSPs). IL-33 is a recently described cytokine that initiates Th2 immune responses through binding to a heterodimeric IL-33Rα (ST2L)/IL-1α accessory protein (IL-1RAcP) receptor that coordinates activation of ERK and NF-κB pathways. We demonstrate here that DUSP5 is expressed in eosinophils, is upregulated following IL-33 stimulation and regulates IL-33 signaling. Dusp5(-/-) mice have prolonged eosinophil survival and enhanced eosinophil effector functions following infection with the helminth Nippostrongylus brasiliensis. IL-33-activated Dusp5(-/-) eosinophils exhibit increased cellular ERK1/2 activation and BCL-XL expression that results in enhanced eosinophil survival. In addition, Dusp5(-/-) eosinophils demonstrate enhanced IL-33-mediated activation and effector functions. Together, these data support a role for DUSP5 as a novel negative regulator of IL-33-dependent eosinophil function and survival.

A specificity map for the PDZ domain family.

PDZ domains are protein-protein interaction modules that recognize specific C-terminal sequences to assemble protein complexes in multicellular organisms. By scanning billions of random peptides, we accurately map binding specificity for approximately half of the over 330 PDZ domains in the human and Caenorhabditis elegans proteomes. The domains recognize features of the last seven ligand positions, and we find 16 distinct specificity classes conserved from worm to human, significantly extending the canonical two-class system based on position -2. Thus, most PDZ domains are not promiscuous, but rather are fine-tuned for specific interactions. Specificity profiling of 91 point mutants of a model PDZ domain reveals that the binding site is highly robust, as all mutants were able to recognize C-terminal peptides. However, many mutations altered specificity for ligand positions both close and far from the mutated position, suggesting that binding specificity can evolve rapidly under mutational pressure. Our specificity map enables the prediction and prioritization of natural protein interactions, which can be used to guide PDZ domain cell biology experiments. Using this approach, we predicted and validated several viral ligands for the PDZ domains of the SCRIB polarity protein. These findings indicate that many viruses produce PDZ ligands that disrupt host protein complexes for their own benefit, and that highly pathogenic strains target PDZ domains involved in cell polarity and growth.

Immune diversity sheds light on missing variation in worldwide genetic diversity panels.

Defining worldwide human genetic variation is a critical step to reveal how genome plasticity contributes to disease. Yet, there is currently no metric to assess the representativeness and completeness of current and widely used data on genetic variation. We show here that Human Leukocyte Antigen (HLA) genes can serve as such metric as they are both the most polymorphic and the most studied genetic system. As a test case, we investigated the 1,000 Genomes Project panel. Using high-accuracy in silico HLA typing, we find that over 20% of the common HLA variants and over 70% of the rare HLA variants are missing in this reference panel for worldwide genetic variation, due to undersampling and incomplete geographical coverage, in particular in Oceania and West Asia. Because common and rare variants both contribute to disease, this study thus illustrates how HLA diversity can detect and help fix incomplete sampling and hence accelerate efforts to draw a comprehensive overview of the genetic variation that is relevant to health and disease.

Control of IL-2Ralpha gene expression: structural changes within the proximal enhancer/core promoter during T-cell development.

During T-cell development in thymus, CD25, the IL-2 receptor alpha chain (IL-2Ralpha) is already expressed in early double-negative (DN) thymocytes where commitment to T-cell lineage has been established, but subsequently IL-2Ralpha is dramatically down-regulated for the remainder of T-cell development. The loss of IL-2Ralpha expression after expression of the pre-TCR alpha:beta complex on the cell surface is essential for the later specific responses of mature T cells. Using appropriate mouse models and DMS genomic footprinting, we showed that the TATA box in the core promoter region of the murine IL-2Ralpha locus was occupied only in DN CD25+ T cells. Further, by chromatin immunoprecipitation assays, we evidenced that down-regulation of IL-2Ralpha transcription correlated with (i) loss of the basal transcriptional machinery; (ii) dissociation of histone acetylase p300 and BRG1, a member of the ATP-dependent chromatin remodeling complex SWI/SNF; and (iii) histone N-termini dephosphorylation plus deacetylation. In contrast, occupancy of the proximal enhancer region (positive regulatory region I) was not detected by in vivo genomic footprinting though constitutive accessibility of the promoter region for DNase I digestion both in the DN and double-positive stages correlated with the constitutive association of CBP and PCAF to the IL-2Ralpha core promoter. These results exemplify one mechanism by which a promoter enables transcription to switch on and off during T-cell differentiation.

Promoter activation by enhancer-dependent and -independent loading of activator and coactivator complexes.

Activation of the pDbeta1 promoter at the TCRbeta locus requires a functional distal enhancer, Ebeta. Here, we have analyzed the mechanism of promoter activation in thymocytes from mice containing or lacking Ebeta. We found that pDbeta1 shows a complex profile of transcription factor and chromatin remodeling complex occupancy even at Ebeta(-) alleles. The presence of Ebeta, however, results in a few specific changes in factor occupancy at the promoter. These differences correlate with localized alterations in histone modifications and in the recruitment of the basal transcriptional machinery. In addition, Ebeta is also bound by CBP and Pol II, suggesting a mechanism for delivery of a holoenzyme complex to the pDbeta1 promoter. These results illustrate a specialized, long-range function of an enhancer in the hierarchical events that regulate assembly of a cell type-specific promoter.