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

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Abstract
Background. We observed IgM deposits in the macula densa of the distal convoluted tubule in some renal biopsies with mesangial IgM deposits and did a systematic study to investigate the frequency of this phenomenon. We compared the findings with those in IgA disease. Methods. A total of 30 renal biopsies with either isolated predominantly mesangial 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 showed weak deposits in the macula densa on immunoperoxidase staining. A total 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 macula densa with mesangial IgM, and suggest that mesangial IgM deposits may be a reflection of non‐specific macromolecule transport rather than an immune reactant.