Immunotactoid glomerulopathy: clinicopathologic and proteomic study

Immunotactoid glomerulopathy (ITG) is a rare glomerular disease. Here, we report the largest clinicopathologic series of ITG and define its proteomic profile. The characteristics of 16 ITG patients who were identified from our pathology archives are provided between 1993 and 2011. We also performed laser microdissection and mass spectrometry (LMD/MS) in three cases. Presentation included proteinuria (100), nephrotic syndrome (69), renal insufficiency (50) and microhematuria (80). Hypocomplementemia was present in 46 and a serum M-spike in 63. Hematologic malignancy was present in 38, including chronic lymphocytic leukemia in 19, lymphoplasmacytic lymphoma in 13 and myeloma in 13. The pattern of glomerular injury was membranoproliferative (56), membranous (31) or proliferative (13) glomerulonephritis. The microtubular deposits were immunoglobulin light chain restricted in 69 and had a mean diameter of 31 nm (range 1752). During an average of 48 months of follow-up for 12 patients, 50 had remission, 33 had persistent renal dysfunction and 17 progressed to end-stage renal disease. Proteomic analysis by LMD/MS revealed the presence of immunoglobulins, monotypic light chains, complement factors of the classical and terminal pathway and small amount of serum amyloid P-component. Hematologic malignancy, particularly lymphoma, is not uncommon in ITG. ITG appears to have a better prognosis than other paraprotein-related renal lesions, with a half of patients expected to recover kidney function with immunosuppressive therapy or chemotherapy. The proteomic profile of ITG is consistent with deposition of monotypic immunoglobulins and activation of the classical and terminal pathway of complement.