PMC:3845430 / 3578-4926 JSONTXT

{"project":"2_test","denotations":[{"id":"24324289-12139942-25763390","span":{"begin":654,"end":656},"obj":"12139942"},{"id":"24324289-16418203-25763391","span":{"begin":658,"end":660},"obj":"16418203"},{"id":"24324289-63917-25763392","span":{"begin":771,"end":773},"obj":"63917"},{"id":"24324289-214511-25763393","span":{"begin":775,"end":777},"obj":"214511"},{"id":"24324289-16418203-25763394","span":{"begin":917,"end":919},"obj":"16418203"},{"id":"24324289-22155016-25763395","span":{"begin":1017,"end":1019},"obj":"22155016"},{"id":"24324289-22155016-25763396","span":{"begin":1327,"end":1329},"obj":"22155016"}],"text":"3. Rheumatoid Factors in Nonrheumatic Conditions \nAs shown in Table 1, RFs can be detected in patients with many nonrheumatic conditions. Infections and chronic diseases may be characterised by the presence of serum RFs, but unlike those detected in RA patients, the RFs produced during infections are usually transient and not detrimental. Given the ability of RFs to increase the clearance of immune complexes and the fact that RF-producing B cells may behave as antigen-presenting cells (APCs) and aid the immune response against the infectious antigens, it is likely that the net impact of RF production during infections is protective for the host [24, 26].\nThese natural RFs are generally low-affinity, polyreactive IgM antibodies produced by CD5-positive B cells [27, 28], and coexistence of RF-positive B cells and nonautoimmune IgG antigen in healthy subjects suggests the existence of tolerance mechanisms [26]. \nRFs can be found in 40–50% of patients with HCV infection, but their frequency can reach 76% [29]. Their production is probably due to chronic stimulation of the immune system by HCV, and, as HCV infection is highly prevalent in various countries (1.5–3% in southern Europe) and represents the first cause of increased serum RFs, HCV antibodies should be sought in all subjects with increased RF levels [29, 30] (Figure 1).\n\n"}