The human microbiome consists of all microorganisms occupying the skin, mucous membranes and intestinal tract of the human body. The contact of the mucosal immune system with the human microbiome is a balanced interplay between defence mechanisms of the immune system and symbiotic or pathogenic microbial factors, such as microbial antigens and metabolites. In systemic autoimmune diseases (SADs) such as rheumatoid arthritis, systemic lupus erythematosus and Sjögren's syndrome, the immune system is deranged to a chronic inflammatory state and autoantibodies are an important hallmark. Specific bacteria and/or a dysbiosis in the human microbiome can lead to local mucosal inflammation and increased intestinal permeability. Proinflammatory lymphocytes and cytokines can spread to the systemic circulation and increase the risk of inflammation at distant anatomical sites, such as the joints or salivary glands. Increased intestinal permeability increases antigen exposure and the risk of autoantibody production. If the human microbiome indeed plays such a critical role in SADs, this finding holds a great promise for new therapeutic strategies, such as diet interventions and probiotics and prebiotics. This review provides a background on the human microbiome and mucosal immunity in the gut and oral cavity and gives a summary of the current knowledge on the microbiome–SADs connection.

The degradation of neoagarotetraose and neoagarobiose by Cytophaga flevensis was investigated. The organism possesses an enzyme that hydrolyzes the tetramer by cleavage of its central beta-galactosidic linkage. The product of this reaction, neoagarobiose, is further hydrolyzed enzymatically to D-galactose and 3,6-anhydro-L-galactose. Both enzyme activities were localized in the cytoplasm. Attempts were made to partially purify the respective enzymes and although a 30-40 fold-purification was achieved, the final preparation contained both neoagarotetra-ase and neoagarobiase activities. Evidence was obtained that these activities were due to different enzymes. Neoagarotetra-ase is highly specific for oligosaccharides containing neoagarobiose units; the rate of hydrolysis is greatest with neoagarotetraose. It cannot hydrolyze pyruvated neoagarotetraose. Optimal conditions for its activity were pH 7.0 and 25 C. Neoagarobiase hydrolyzes only neoagarobiose and neoagarobiitol and optimal conditions for activity were pH 6.75 and 25 C. Both enzymes were inhibited by Ag+, Hg2+ and Zn2+ ions and by p-CMB, which indicates that thiol groups are present in their active centres. Both enzymes were induced by neoagaro-oligosaccharides and melibiose and were repressed when glucose was added to the medium. Neoagarobiase was also induced by D-galacturonic acid. In continuous culture, the rate of enzyme production was maximal at a dilution rate of 0.1 h-1.

Genome-wide association studies (GWAS) have identified hundreds of loci associated with Crohns disease (CD); however, as with all complex diseases, deriving pathogenic mechanisms from these non-coding GWAS discoveries has been challenging. To complement GWAS and better define actionable biological targets, we analysed sequence data from more than 30,000 CD cases and 80,000 population controls. We observe rare coding variants in established CD susceptibility genes as well as ten genes where coding variation directly implicates the gene in disease risk for the first time.