Association of mesangial IgM with IgM deposits in the macula densa: an indication of non-specific macromolecule transport rather than immune reactant?

Background. We observed IgM deposits in the macula densa of the distal conv oluted tubule in some renal biopsies with mesangial IgM deposits and did a systematic study to investigate the frequency of this phenomenon. We compar ed the findings with those in IgA disease. Methods. A total of 30 renal biopsies with either isolated predominantly me sangial IgM, or mesangial IgA (+/- IgM) deposition, were retrieved from the files and reviewed independently by both authors. Results. Eight showed strong macula densa IgM deposits and another three sh owed weak deposits in the macula densa on immunoperoxidase staining. A tota l of 14 biopsies also showed mesangial IgA deposition but IgA was not seen in the macula densa. Conclusions. These results confirm the association of Igm deposits in the m acula densa with mesangial IgM and suggest that mesangial IgM deposits may be a reflection of non-specific macromolecule transport rather than an immu ne reactant.