Abnormalities of IgA1 production in IgA nephropathy

SUMMARY: IgA nephropathy (IgAN) is characterized by the mesangial deposition of polymeric IgA1 (plgA1). the original view that this plgA1 is derived from the mucosal immune system can no longer be sustained. Studies of duodenal mucosa and marrow indicate increased production of plgA1 in the marrow and decreased production in the mucosa. These changes are consistent with immunization studies showing exaggerated and prolonged plgA responses to systemic immunization, and reduced mucosal responses to mucosal neoantigens. However, the IgA1 and IgG systemic responses to mucosal antigen are increased in IgAN, a finding consistent with impairment in oral tolerance, the process by which systemic immune responses, to mucosal antigen challenge are normally suppressed. Both IgA1 production and the induction of oral tolerance are under T-cell control. T-cell populations involved in these processes include γδ T cells, Tr cells and T-helper (Th)3 cells; cytokines with a key role in the control of IgA production include interleukin (IL)-10 and transforming growth factor (TGF)-β. There is evidence of abnormal γδ T-cell V region usage in both mucosa and marrow in IgAN. Increased expression of relevant cytokines has also been reported in circulating T cells in IgAN. the increased O-glycosylation of circulating IgA1 in IgAN may also be further evidence of a shift in the production of mucosal-type plgA1 from the mucosa to marrow. These findings suggest that the specific lymphocyte homing mechanisms that normally maintain oral tolerance and control the site of IgA production require further study in IgAN.