Tubulointerstitial Nephritis with IgM-Positive Plasma Cells

Area of Science:

• Nephrology
• Immunopathology
• Renal Pathology

Background:

• Tubulointerstitial nephritis (TIN) is commonly associated with IgG-positive plasma cells.
• IgM-positive plasma cell infiltration in TIN is rare and often undetected by standard methods.
• Immunoenzyme methods on paraffin-embedded sections are superior for detecting specific plasma cell types in renal tissue.

Purpose of the Study:

• To investigate the clinicopathologic features of tubulointerstitial nephritis with IgM-positive plasma cell infiltration.
• To establish a distinct diagnostic entity for this specific form of TIN.
• To explore the diagnostic utility of immunoenzyme methods in identifying histologic variants of TIN.

Main Methods:

• Nationwide search for patients with biopsy-proven TIN and high serum IgM levels.
• Confirmation of IgM-positive plasma cell infiltration using immunoenzyme methods on formalin-fixed, paraffin-embedded renal sections.
• Analysis of clinical data, including renal tubular function and autoantibodies.
• Histopathological examination of renal biopsies, including immunophenotyping of inflammatory infiltrates and assessment of tubular transporters.

Main Results:

• Identified 13 patients with TIN characterized by IgM-positive plasma cell infiltration.
• High prevalence of distal renal tubular acidosis (100%) and Fanconi syndrome (92%) in affected patients.
• Consistent finding of interstitial nephritis with CD3-positive T lymphocytes and colocalized IgM-positive plasma cells.
• Marked decrease in renal tubular transporter levels (H+-ATPase, H+, K+-ATPase, HCO3--Cl- anion exchanger) in collecting ducts.

Conclusions:

• A distinct clinicopathologic entity, IgM-positive plasma cell-tubulointerstitial nephritis, is proposed.
• This condition is characterized by specific clinical manifestations and distinct histopathological findings.
• Immunoenzyme techniques are crucial for diagnosing this previously under-recognized variant of TIN.