Reduced systemic IgG levels against peptidoglycan in rheumatoid arthritis (RA) patients

The gut flora is believed to play a role in the pathogenesis of RA. Peptido glycan, a major cell wall component of Gram-positive bacteria, is a candida te antigen because of its capability to trigger production of proinflammato ry cytokines, to induce arthritis in rodents, and because of its presence i n antigen-presenting cells in RA joints. We investigated whether the system ic and local antibody levels against a peptidoglycan-polysaccharide (PG-PS) are related to the presence and disease activity of RA. Significantly lowe r levels of systemic IgG directed against PG-PS were found in healthy femal es compared with healthy males, and systemic IgA levels specific for PG-PS were negatively correlated with age. Levels of systemic IgG directed agains t PG-PS were significantly reduced in RA patients compared with sex- and ag e-matched healthy controls. Local (synovial fluid) levels of IgG did not co rrelate with disease activity whereas synovial fluid levels of IgA correlat ed positively with disease activity. These data suggest that IgG in healthy people mediates protection against spreading of PG to non-mucosal sites.