coliO111 LPS antibody was used as a reference to compare OD values in the same plate. were used as controls. == Results == Statistically significant reduction of arthritis symptoms and improvement of intestinal disorders were observed only in the test group: effective in 8 (44%), possibly effective in 2 (12%) and not effective in 8 (44%) of 18 patients treated (2 patients withdrew) based on anad hoc”evaluation point”, the sum of variables that are improved more than 20% among the 8 core variables used for the American College of Rheumatology (ACR) response criteria. This disease modifying effect of the WPC disappeared upon cessation 5′-GTP trisodium salt hydrate of treatment, but was reappeared upon reintroduction of it. Importantly, 7 of 8 non-responders carry DR15 haplotype (DRB1-1501 and 1502), whereas only 1 1 of 7 responders was DR15 positive (risk ratio: 6.1). Furthermore, the pre-clinical serum anti-LPS and anti-type II collagen antibody levels in the responders were higher or tended to be higher than those in the non-responders, suggesting that there are 2 sub-types of RA based on an interaction between gastrointestinal pathogens and MHC class II haplotypes. == Conclusions == The natural milk antibody preparation containing high levels antibodies against pathogenic enteromicrobes and their toxins seems to be effective in 5′-GTP trisodium salt hydrate a certain RA subset, and deserves more attention as a potential adjunct in the treatment of RA. == Trial Registration Number == UMIN000003128 == Background == The disease causative factor of rheumatoid arthritis (RA) remains unknown regardless of extensive studies on candidate antigens[1-5] and disease susceptibility [6,7]. Recently, some consideration has been given to environmental factors, particularly commensal bacteria in the gastrointestinal 5′-GTP trisodium salt hydrate (GI) tract [8,9]. For example, it has been shown that bacterial cell wall components, such as enterobacterial common antigens [10] and peptidoglycan-polysaccharide polymers, can induce arthritis [11,12] and uveitis [13] in experimental animals. GI bacteria and their toxins such as lipopolysaccharides (LPS: gram-negative bacteria cell wall components) apparently contribute to the development and exacerbation of autoimmune diseases in experimental models such as autoimmune thyroiditis in rats [14] and autoimmune hemolytic anemia (AIHA) in mice [15,16]. In clincal studies, it has also been suggested that commensal bacteria may play a pathogenic role in patients with RA. Aokiet al. reported that some patients with RA were sensitized to enterobacterial common antigens (35 and 38 kDa outer membrane protein) [10]. Van der Heijden and coworkers reported that degradation products of bacterial cell walls and nucleic acids were found in RA joints Col18a1 [17]. Imbalance of intestinal bacteria has even been suggested as a possible etiopathogenic or aggravating factor in RA based on the observation that modulation of the intestinal bacterial flora by a vegetarian diet was associated with clinical improvement [18-20]. Unfortunately, these observations were not acknowledged by researchers in the fields of immunology and rheumatology, because of the difficulty of handling and analyzing intestinal bacteria. However, Vaahtovuoet al. [21] recently reported thatBifidobacteria, bacteria of theBacteroides-Porphyromonas-Prevotellagroup,Bacteroides fragilissubgroup, andEubacterium rectale-Clostridium coccoidesgroup were significantly less numerous in early RA than in controls as determined by flow cytometry analysis of 16 S rRNA hybridized and DNA-stained fecal bacteria. Based on our [4,5,22,23] and other previous studies [24], it has been hypothesized that the increased permeability of the GI mucosa relating 5′-GTP trisodium salt hydrate to a lowered immune function of gut associated lymphoid tissues (GALT) could modulate rheumatoid disease activity [25]. For example, excess amounts of bacteria toxins absorbed from the GI mucosa may directly stimulate the release of pro-inflammatory cytokines such as tumour necrosis factor (TNF), interleukin-1 (IL-1) 5′-GTP trisodium salt hydrate [26], and high mobility group box-1 (HMGB1) protein [27], which could exacerbate inflammatory reactions [23,28,29], but also systemically affect the host’s immune system for prolonged periods as non-specific immunostimulants. The GI bacterial balance is modulated by interactions between pathogenic and non-pathogenic bacteria and by the host’s immune function. Therefore, it is rational to consider how to alter or normalize intestinal environmental conditions by foods rather than antibiotics, since it is apparent that nutritional components apparently affect the intestinal bacterial flora population. In this aspect, we focused on natural milk antibodies, which recognize a wide spectrum of pathogenic entromicrobes and their toxins. Accordingly, we prepared a whey protein concentrate (WPC), which contains high levels of bioactive natural antibodies [30], from normal cow milk instead of colostrums using special conditions to avoid heat denaturation of immunoglobulins. This WPC was tested in elderly volunteers, and the test results clearly indicated that bioactive natural milk antibody preparation is capable of modulating intestinal bacterial flora, e.g. decreasing the population ofE. coliandClostridium perfringens(formally knownClostridium welchii) by 50 and.