Systemic and mucosal IgA responses to systemic antigen challenge in IgA nephropathy.

IgA nephropathy (IgAN) is characterized by the deposition of glomerular IgA. The source of the deposited IgA is not known, but both the mucosal and systemic IgA systems have been implicated. In order to investigate mucosal and systemic antibody production to systemic antigen challenge in IgAN, 20 patients and 20 controls where immunized with tetanus toxoid (TT). While patients with IgAN responded with a similar serum IgG, IgA, IgA1, and IgA2 antibody response to controls, they did, however, produce more IgA1 antibodies relative to IgA2 (P < 0.05). No salivary IgA antibody response was observed to systemic immunization in controls; however, there was a significant IgA response to TT in the saliva of patients with IgAN. IgA antibodies were produced in vitro by Epstein Barr virus (EBV)-transformed peripheral blood lymphocytes (PBLs) obtained from control blood only when taken shortly (1 or 2 weeks) after immunization. Patients with IgAN produced significantly more IgA anti-TT positive cultures than controls and for a longer period (P < 0.01) after immunization. In contrast, IgG anti-TT was produced in EBV-transformed cultures at all time points, but with no difference between IgAN and controls in the proportion of IgG producing cultures. These results demonstrate increased IgA antibody production in both the systemic and mucosal IgA systems following systemic immunization in IgAN and suggest an abnormal overlap between the two systems in IgAN.