Clinical and biochemical footprints of inherited metabolic diseases. XII. Immunological defects.

Immunological problems are increasingly acknowledged manifestations in many inherited metabolic diseases (IMDs), ranging from exaggerated inflammation, autoimmunity and abnormal cell counts to recurrent microbial infections. A subgroup of IMDs, the congenital disorders of glycosylation (CDG), includes CDG types that are even classified as primary immunodeficiencies. Here, we reviewed the list of metabolic disorders reported to be associated with various immunological defects and identified 171 IMDs accompanied by immunological manifestations. Most IMDs are accompanied by immune dysfunctions of which immunodeficiency and infections, innate immune defects, and autoimmunity are the most common abnormalities reported in 144/171 (84%), 44/171 (26%) and 33/171 (19%) of IMDs with immune system involvement, respectively, followed by autoinflammation 17/171 (10%). This article belongs to a series aiming at creating and maintaining a comprehensive list of clinical and metabolic differential diagnoses according to organ system involvement.

Evaluation of Cell Models to Study Monocyte Functions in PMM2 Congenital Disorders of Glycosylation.

Congenital disorders of glycosylation (CDG) are inherited metabolic diseases characterized by mutations in enzymes involved in different steps of protein glycosylation, leading to aberrant synthesis, attachment or processing of glycans. Recently, immunological dysfunctions in several CDG types have been increasingly documented. Despite these observations, detailed studies on immune cell dysfunction in PMM2-CDG and other CDG types are still scarce. Studying PMM2-CDG patient immune cells is challenging due to limited availability of patient material, which is a result of the low incidence of the disease and the often young age of the subjects. Dedicated immune cell models, mimicking PMM2-CDG, could circumvent many of these problems and facilitate research into the mechanisms of immune dysfunction. Here we provide initial observations about the immunophenotype and the phagocytic function of primary PMM2-CDG monocytes. Furthermore, we assessed the suitability of two different glycosylation-impaired human monocyte models: tunicamycin-treated THP-1 monocytes and PMM2 knockdown THP-1 monocytes induced by shRNAs. We found no significant differences in primary monocyte subpopulations of PMM2-CDG patients as compared to healthy individuals but we did observe anomalous surface glycosylation patterns in PMM2-CDG patient monocytes as determined using fluorescent lectin binding. We also looked at the capacity of monocytes to bind and internalize fungal particles and found a slightly increased uptake of C. albicans by PMM2-CDG monocytes as compared to healthy monocytes. Tunicamycin-treated THP-1 monocytes showed a highly decreased uptake of fungal particles, accompanied by a strong decrease in glycosylation levels and a high induction of ER stress. In contrast and despite a drastic reduction of the PMM2 enzyme activity, PMM2 knockdown THP-1 monocytes showed no changes in global surface glycosylation levels, levels of fungal particle uptake similar to control monocytes, and no ER stress induction. Collectively, these initial observations suggest that the absence of ER stress in PMM2 knockdown THP-1 cells make this model superior over tunicamycin-treated THP-1 cells and more comparable to primary PMM2-CDG monocytes. Further development and exploitation of CDG monocyte models will be essential for future in-depth studies to ultimately unravel the mechanisms of immune dysfunction in CDG.

Biological and Technical Challenges in Unraveling the Role of N-Glycans in Immune Receptor Regulation.

N-glycosylation of membrane receptors is important for a wide variety of cellular processes. In the immune system, loss or alteration of receptor glycosylation can affect pathogen recognition, cell-cell interaction, and activation as well as migration. This is not only due to aberrant folding of the receptor, but also to altered lateral mobility or aggregation capacity. Despite increasing evidence of their biological relevance, glycosylation-dependent mechanisms of receptor regulation are hard to dissect at the molecular level. This is due to the intrinsic complexity of the glycosylation process and high diversity of glycan structures combined with the technical limitations of the current experimental tools. It is still challenging to precisely determine the localization and site-occupancy of glycosylation sites, glycan micro- and macro-heterogeneity at the individual receptor level as well as the biological function and specific interactome of receptor glycoforms. In addition, the tools available to manipulate N-glycans of a specific receptor are limited. Significant progress has however been made thanks to innovative approaches such as glycoproteomics, metabolic engineering, or chemoenzymatic labeling. By discussing examples of immune receptors involved in pathogen recognition, migration, antigen presentation, and cell signaling, this Mini Review will focus on the biological importance of N-glycosylation for receptor functions and highlight the technical challenges for examination and manipulation of receptor N-glycans.

Publisher Correction: Clonal analysis of Salmonella-specific effector T cells reveals serovar-specific and cross-reactive T cell responses.

In the version of this article initially published, the first affiliation lacked 'MRC'; the correct name of the institution is 'MRC Weatherall Institute of Molecular Medicine'. Two designations (SP110Y and ST110H) were incorrect in the legend to Fig. 6f,h,i. The correct text is as follows: for panel f, "...loaded with either the CdtB(105-125)SP110Y (DRB4*SP110Y) or the CdtB(105-125)ST110H (DRB4*ST110H) peptide variants..."; for panel h, "...decorated by the DRB4*SP110Y tetramer (lower-right quadrant), the DRB4*ST110H (upper-left quadrant)..."; and for panel i, "...stained ex vivo with DRB4*SP110Y, DRB4*ST110H...". In Fig. 8e, the final six residues (LTEAFF) of the sequence in the far right column of the third row of the table were missing; the correct sequence is 'CASSYRRTPPLTEAFF'. In the legend to Fig. 8d, a designation (HLyE) was incorrect; the correct text is as follows: "(HlyE?)." Portions of the Acknowledgements section were incorrect; the correct text is as follows: "This work was supported by the UK Medical Research Council (MRC) (MR/K021222/1) (G.N., M.A.G., A.S., V.C., A.J.P.),...the Oxford Biomedical Research Centre (A.J.P., V.C.),...and core funding from the Singapore Immunology Network (SIgN) (E.W.N.) and the SIgN immunomonitoring platform (E.W.N.)." Finally, a parenthetical element was phrased incorrectly in the final paragraph of the Methods subsection "T cell cloning and live fluorescence barcoding"; the correct phrasing is as follows: "...(which in all cases included HlyE, CdtB, Ty21a, Quailes, NVGH308, and LT2 strains and in volunteers T5 and T6 included PhoN)...". Also, in Figs. 3c and 4a, the right outlines of the plots were not visible; in the legend to Fig. 3, panel letter 'f' was not bold; and in Fig. 8f, 'ND' should be aligned directly beneath DRB4 in the key and 'ND' should be removed from the diagram at right, and the legend should be revised accordingly as follows: "...colors indicate the HLA class II restriction (gray indicates clones for which restriction was not determined (ND)). Clonotypes are grouped on the basis of pathogen selectivity (continuous line), protein specificity (dashed line) and epitope specificity; for ten HlyE-specific clones (pixilated squares), the epitope specificity was not determined...". The errors have been corrected in the HTML and PDF versions of the article.

Clonal analysis of Salmonella-specific effector T cells reveals serovar-specific and cross-reactive T cell responses.

To tackle the complexity of cross-reactive and pathogen-specific T cell responses against related Salmonella serovars, we used mass cytometry, unbiased single-cell cloning, live fluorescence barcoding, and T cell-receptor sequencing to reconstruct the Salmonella-specific repertoire of circulating effector CD4+ T cells, isolated from volunteers challenged with Salmonella enterica serovar Typhi (S. Typhi) or Salmonella Paratyphi A (S. Paratyphi). We describe the expansion of cross-reactive responses against distantly related Salmonella serovars and of clonotypes recognizing immunodominant antigens uniquely expressed by S. Typhi or S. Paratyphi A. In addition, single-amino acid variations in two immunodominant proteins, CdtB and PhoN, lead to the accumulation of T cells that do not cross-react against the different serovars, thus demonstrating how minor sequence variations in a complex microorganism shape the pathogen-specific T cell repertoire. Our results identify immune-dominant, serovar-specific, and cross-reactive T cell antigens, which should aid in the design of T cell-vaccination strategies against Salmonella.