Riboflavin Metabolism Variation among Clinical Isolates of Streptococcus pneumoniae Results in Differential Activation of Mucosal-associated Invariant T Cells.

Streptococcus pneumoniae is an important bacterial pathogen that causes a range of noninvasive and invasive diseases. The mechanisms underlying variability in the ability of S. pneumoniae to transition from nasopharyngeal colonization to disease-causing pathogen are not well defined. Mucosal-associated invariant T (MAIT) cells are prevalent in mucosal tissues such as the airways and are believed to play an important role in the early response to infection with bacterial pathogens. The ability of MAIT cells to recognize and contain infection with S. pneumoniae is not known. In the present study, we analyzed MAIT-cell responses to infection with clinical isolates of S. pneumoniae serotype 19A, a serotype linked to invasive pneumococcal disease. We found that although MAIT cells were capable of responding to human dendritic and airway epithelial cells infected with S. pneumoniae, the magnitude of response to different serotype 19A isolates was determined by genetic differences in the expression of the riboflavin biosynthesis pathway. MAIT-cell release of cytokines correlated with differences in the ability of MAIT cells to respond to and control S. pneumoniae in vitro and in vivo in a mouse challenge model. Together, these results demonstrate first that there are genetic differences in riboflavin metabolism among clinical isolates of the same serotype and second that these likely determine MAIT-cell function in response to infection with S. pneumoniae. These differences are critical when considering the role that MAIT cells play in early responses to pneumococcal infection and determining whether invasive disease will develop.

TCRß Combinatorial Immunoreceptor Expression by Neutrophils Correlates with Parasite Burden and Enhanced Phagocytosis during a Plasmodium berghei ANKA Malaria Infection.

Recent studies have demonstrated that a subpopulation of neutrophils express the TCRαß combinatorial immunoreceptor in humans and mice. Here, we report that a Plasmodium berghei ANKA murine malaria infection induces expansion of TCRß expressing CD11b+ Ly6G+ neutrophils in the spleen during the early phase of infection. Measurement of TCRß transcript and protein levels of neutrophils in wild-type versus nude and Rag1 knockout mice establishes that the observed expression is not a consequence of nonspecific antibody staining or passive receptor expression due to phagocytosis or trogocytosis of peripheral T cells. Remarkably, on day 3 postinfection, we observed a highly significant correlation between the proportion of neutrophils that express TCRß and peripheral blood parasite burden. In addition, TCRß+ neutrophils phagocytose parasitized erythrocytes with 4-fold greater efficiency than TCRß- neutrophils. Together these results signify that TCR expression by the neutrophil plays an important role in the regulation of parasite burden by enhancing the phagocytic capacity of the neutrophil.

The promise of amplification assays for accurate early detection of α-synucleinopathies: A review.

Lewy body dementia encompasses the common neurodegenerative disorders Dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD). Lewy Body disease (LBD) is characterized by abnormal aggregates of α-synuclein (α-syn) in the brain which form Lewy bodies. LBD is commonly misdiagnosed/underdiagnosed, especially in early stages. There remains a great need for reliable biomarkers to assist with LBD diagnosis. Amplification techniques such as real-time quaking-induced conversion (RT-QuIC) and protein misfolding cyclic amplification (PMCA) represent an important advance for biomarker detection. Amplification assays detect the ability of pathogenic protein to induce conformational change in normal protein; α-syn has been shown to propagate in a prion-like manner, making it a candidate for such analysis. In this review, we describe the diagnostic potential of amplification techniques for differentiating α-synucleinopathies from other neurodegenerative disorders such as Alzheimer's disease (AD), frontotemporal dementia (FTD), progressive supranuclear palsy (PSP), corticobasal syndrome (CBS), and atypical parkinsonism, as well as α-synucleinopathies from each other. Recent studies report accurate detection of α-syn seeding activity in human tissues such as cerebrospinal fluid (CSF), submandibular gland (SMG), and posterior cervical skin. Adaptation to clinical settings may present challenges. However, the high accuracy of recent results, combined with the success of amplification assay diagnostics in clinical practice for Creutzfeldt-Jakob disease, suggest high promise for eventual clinical application.

Rab6 regulates recycling and retrograde trafficking of MR1 molecules.

Mucosal-associated invariant T (MAIT) cells are an innate-like T cell subset important in the early response to bacterial and viral lung pathogens. MAIT cells recognize bacterial small molecule metabolites presented on the Class I-like molecule MR1. As with other Class I and Class II molecules, MR1 can likely sample ligands in the intracellular environment through multiple cellular pathways. Rab6, a small GTPase that regulates a number of endosomal trafficking pathways including retrograde transport to the trans-Golgi network (TGN), is involved in the presentation of ligands from Mycobacterium tuberculosis (Mtb) to MAIT cells. The Rab6-mediated trafficking pathway contains endosomal compartments that share features with the Mtb intracellular compartment. Using inducible expression of MR1, this study demonstrates that Rab6 regulates the recycling of MR1 molecules from the cell surface through endosomal trafficking compartments to the TGN. This Rab6-dependent pool of recycled MR1, which is available for reloading with ligands from bacterial pathogens like Mtb, may be important for early recognition of infected cells by MAIT cells in the lung.

Alternative splicing of MR1 regulates antigen presentation to MAIT cells.

Mucosal Associated Invariant T (MAIT) cells can sense intracellular infection by a broad array of pathogens. These cells are activated upon encountering microbial antigen(s) displayed by MR1 on the surface of an infected cell. Human MR1 undergoes alternative splicing. The full-length isoform, MR1A, can activate MAIT cells, while the function of the isoforms, MR1B and MR1C, are incompletely understood. In this report, we sought to characterize the expression and function of these splice variants. Using a transcriptomic analysis in conjunction with qPCR, we find that that MR1A and MR1B transcripts are widely expressed. However only MR1A can present mycobacterial antigen to MAIT cells. Coexpression of MR1B with MR1A decreases MAIT cell activation following bacterial infection. Additionally, expression of MR1B prior to MR1A lowers total MR1A abundance, suggesting competition between MR1A and MR1B for either ligands or chaperones required for folding and/or trafficking. Finally, we evaluated CD4/CD8 double positive thymocytes expressing surface MR1. Here, we find that relative expression of MR1A/MR1B transcript is associated with the prevalence of MR1 + CD4/CD8 cells in the thymus. Our results suggest alternative splicing of MR1 represents a means of regulating MAIT activation in response to microbial ligand(s).