The possible involvement of intestine-derived IgA₁: A case of IgA nephropathy associated with Crohn's disease

Background: A link between IgA nephropathy and Crohn's disease has recently been reported. Other researchers hypothesize that intestine-derived IgA complexes deposit in glomerular mesangial cells, eliciting IgA nephropathy. Intestinal mucosal plasma cells mainly secrete IgA₂. Nevertheless, IgA₁ deposition is strongly implicated as being the primary cause of IgA nephropathy. Case presentation: A 46-year-old Japanese man developed IgA nephropathy 29 years ago, following tonsillectomy. As a result, a normal urinalysis was obtained. The patient previously suffered Crohn's disease followed by urinary occult blood and proteinuria six years ago. Exacerbation of IgA nephropathy was highly suspected. Therefore a renal biopsy was performed. A diagnosis of exacerbation of IgA nephropathy with mesangial cell proliferation and fibrotic cellular crescent was based upon the pathological findings. The patient exhibited a positive clinical course and eventually achieved a remission with immunosuppressive therapy including prednisolone treatment. Immunostaining for the detection of IgA subtypes was performed on both of his kidney and excised ileum. The results revealed IgA₁ and IgA₂ deposition by submucosal cells in intestine. Furthermore, IgA₁ deposition of mesangial areas in the patient's kidney, indicated an association of IgA₁ with the exacerbation of IgA nephropathy. Conclusion: This case represents the possibility that the intestine-derived IgA₁ can be the origin of galactose-deficient IgA which is known to cause IgA nephropathy exacerbation.