Impaired intracellular pathogen clearance and inflammatory joint disease: Is Whipple's disease a guiding light?

[Co-occurrence of Whipple's disease and hyperparathyroidism - coincidence or causal relationship?]

Whipple's disease is a rare infectious disease with multiple clinical manifestations. The disease is named after George Hoyt Whipple, who first recorded the illness in 1907 after conducting the autopsy of a 36-year-old man with weight loss, diarrhea, and arthritis. Under the microscope, Whipple discovered a rod-shaped bacterium in the patient's intestinal wall, which was not confirmed as a new bacterial species until 1992, when it was named Tropheryma whipplei.Recurrence of Whipple's disease can occur years after an initial diagnosis and often manifests with extraintestinal symptoms such as arthritides or skin efflorescences, years before a gastrointestinal complaint. However, the simultaneous occurrence of primary hyperparathyroidism in the present case is a hitherto unknown clinical picture and opens up new questions and perspectives in the context of diagnostics and therapy.

Contribution of HLA DRB1, PTPN22, and CTLA4, to RA dysbiosis

This narrative review gathers current evidence for a contribution of rheumatoid arthritis (RA) HLA-DRB1, PTPN22 and CTLA4 polymorphisms to the gut dysbiosis observed in RA, especially at its onset (transient excess of Prevotella). The gut microbiome contains elements which are 30% heritable, including genera like Bacteroides and Veillonella, and to a lesser extent Prevotella. The first months/year seems a critical period for the selection of a core of microbiota, that should be considered as a second self by the immune system, and tolerized by regulatory T and B cells. Imperfect tolerization may increase the risk of RA following further repeated silent translocations of various gut microorganisms, including Prevotella copri, from gut to joints (fostered by a concurrent loss in gut mucosa of protective bacteria like Faecalibacterium prausnitzii). Genetics studies confirmed that Prevotella copri was partly heritable, and strong associations were observed between the overall microbial composition of stools and the HLA-DRB1 RA risk allele, either in a US cohort (P=0.00001), or the Twins UK cohort (P=0.033). This finding also stands for persons still free from RA, and was replicated in the Swiss SCREEN-RA cohort. Gene variants of PTPN22 also modify intestinal microbiota composition, compromise granulocyte-mediated antibacterial defence in gut, and reduce the suppressive effect of gut regulatory B cells. CTLA4 variants may similarly contribute to RA dysbiosis, since immunotherapy by CTLA-4 blockade depends on microbiota, and CTLA4 activates T follicular regulatory cells to reduce immune responses to segmented filamentous bacteria. Suggestions for future works are made.

Another Look at the Contribution of Oral Microbiota to the Pathogenesis of Rheumatoid Arthritis: A Narrative Review

Although autoimmunity contributes to rheumatoid arthritis (RA), several lines of evidence challenge the dogma that it is mainly an autoimmune disorder. As RA-associated human leukocyte antigens shape microbiomes and increase the risk of dysbiosis in mucosae, RA might rather be induced by epigenetic changes in long-lived synovial presenting cells, stressed by excessive translocations into joints of bacteria from the poorly cultivable gut, lung, or oral microbiota (in the same way as more pathogenic bacteria can lead to "reactive arthritis"). This narrative review (i) lists evidence supporting this scenario, including the identification of DNA from oral and gut microbiota in the RA synovium (but in also healthy synovia), and the possibility of translocation through blood, from mucosae to joints, of microbiota, either directly from the oral cavity or from the gut, following an increase of gut permeability worsened by migration within the gut of oral bacteria such as Porphyromonas gingivalis; (ii) suggests other methodologies for future works other than cross-sectional studies of periodontal microbiota in cohorts of patients with RA versus controls, namely, longitudinal studies of oral, gut, blood, and synovial microbiota combined with transcriptomic analyses of immune cells in individual patients at risk of RA, and in overt RA, before, during, and following flares of RA.

Contribution of mycobiota to the pathogenesis of spondyloarthritis

This review lists current evidences for a contribution of gut mycobiota to the pathogenesis of SpA and related conditions. Gut mycobiota has a small size as compared to bacterial microbiota, but an even greater inter- and intra-individual variability. Although most fungi (brought by food or air) are only transitory present, a core mycobiota of gut resident fungi exists, and interplays with bacteria in a complex manner. A dysbiosis of this gut mycobiota has been observed in Crohn's disease and sclerosing cholangitis, with decreased proportion of Saccharomyces cerevisiae and outgrowth of more pathogenic gut fungi. Fungal-induced lower number of commensal gut bacteria can promote translocation of some bacterial/fungal antigens through mucosae, and live fungi can also cross the epithelial border in Crohn's disease. This dysbiosis also lower the ability of bacteria to metabolize tryptophan into regulatory metabolites, consequently enhancing tryptophan metabolism within human cells, which might contribute to fatigue. Translocation of mycobiotal antigens like curdlan (beta-glucan), which plays a major role in the pathogenesis of SpA in the SGK mice, has been observed in humans. This translocation of fungal antigens in human SpA might account for the anti-Saccharomyces antibodies found in this setting. Contribution of fungal antigens to psoriasis and hidradenitis suppurativa would fit with the preferential homing of fungi in the skin area most involved in those conditions. Fungal antigens also possess autoimmune uveitis-promoting function. As genes associated with SpA (CARD9 and IL23R) strongly regulate the innate immune response against fungi, further studies on fungi contribution to SpA are needed.

Crossing the boundaries: IL-23 and its role in linking inflammation of the skin, gut and joints

Several lines of evidence point towards the central role of IL-23 as a crucial inflammatory mediator in the pathogenesis of SpA—a group of inflammatory arthritic diseases whose symptoms span the skin, gastrointestinal tract and joints. While therapeutic blockade of IL-23 proved successful in the treatment of IBD, psoriatic skin disease and peripheral SpA, it failed in patients suffering from SpA with predominantly axial involvement. Here we review state-of-the-art discoveries on IL-23 signalling pathways across target tissues involved in SpA. We discuss the discrepancies in resident IL-23–responding cells and their downstream activities across skin, gut and joint that shape the unique immunological landscape of SpA.

Clinical manifestations of Whipple's disease mimicking rheumatic disorders

Whipple’s disease is a rare, chronic, systemic disorder caused by Tropheryma whipplei infection. The most common symptoms are weight loss, arthralgia, diarrhea and abdominal pain. Other organ involvement can also occur in the patients. Joint manifestations may mimic rheumatoid arthritis or spondyloarthritis. Arthalgia, arthritis, spondylodiscitis, bursitis and/or tenosynovitis are seen in the majority of the patients. This explains why some of the symptoms are misdiagnosed as those of rheumatic diseases. Understanding of Whipple’s disease is important for differential diagnostics of several rheumatic symptoms.