Immunofluorescence staining for immunoglobulin heavy chain/light chain on kidney biopsies is a valuable ancillary technique for the diagnosis of monoclonal gammopathy-associated kidney diseases.

Heavy chain/light chain (HLC) antibodies target conformational epitopes at the junctions of the heavy chain and light chain constant regions (CH1 and CL) of serum IgGκ, IgGλ, IgAκ, IgAλ, IgMκ, and IgMλ to provide quantitation of intact HLC pairs. Here, we developed an HLC tissue immunofluorescence protocol to test if it can complement conventional immunofluorescence in the diagnosis of monoclonal gammopathy-associated kidney diseases. HLC immunofluorescence was performed on archived frozen tissue of 104 kidney biopsies. The sensitivity and specificity of HLC immunofluorescence was confirmed by testing cases of lupus nephritis, other polyclonal immunoglobulin nephropathies, and light chain nephropathies (light chain amyloidosis and deposition disease). Testing of ten cases of the IgG variant of proliferative glomerulonephritis with monoclonal immunoglobulin deposits excluded monoclonal deposits in two by revealing positivity for IgGκ and IgGλ. Testing of 12 cases of monotypic IgA nephropathy excluded monoclonal deposits in six by revealing staining for IgAκ and IgAλ. Testing of six cases of monotypic fibrillary glomerulonephritis excluded monoclonal deposits in three by revealing positivity for IgGκ and IgGλ. None of 14 cases of glomerulonephritis in which HLC immunofluorescence unmasked polytypic deposits were associated with a serum or urine monoclonal immunoglobulins matching the conventional immunofluorescence results. HLC immunofluorescence outperformed paraffin immunofluorescence and IgG subclass staining in 10/13 (77%) of cases. Testing of 18 cases of cryoglobulinemic glomerulonephritis showed better correlation with serum cryoprecipitate immunofixation than conventional immunofluorescence with regards to the type of cryoglobulin in 47% of cases. Thus, HLC immunofluorescence is a valuable ancillary technique in kidney pathology for the diagnosis of monoclonal gammopathy-associated nephropathies, and could be utilized to confirm or exclude the monoclonal nature of deposits.