Immunofluorescence on paraffin-embedded sections in evaluation of immune complex deposits in renal biopsy specimens

The data focused on the value of immunofluorescence on paraffin-embedded sections are controversial, and it is still difficult to obtain reproducible results. The aim of our study was to evaluate the usefulness of immunofluorescence on paraffin-embedded renal section in detecting immune complex deposits in IgA nephropathy (n = 24), membranous glomerulopathy (n = 22) and lupus nephritis (n = 24). Our study revealed that direct immunofluorescence on paraffin-embedded sections pre-treated with proteinase K for 30 or 60 min is a less sensitive method than immunofluorescence on frozen sections; therefore a number of glomerulopathies may be overlooked. Immunofluorescence on paraffin sections showed dominant or co-dominant fluorescence of Riga only in 41.7% of cases of Riga nephropathy. In the studied glomerulopathies the number of positive immunofluorescences of IgA, IgG, IgM and C3 was significantly lower in immunofluorescence on paraffin sections in comparison with findings obtained from immunofluorescence on frozen sections. Irrespective of glomerular disease the rate of agreement between immunofluorescence on paraffin sections and immunofluorescence on frozen sections with respect to the presence of IgA was 56.5%, IgM – 44.4%, IgG – 73.9%, and C3 – 51.5%. In conclusion, our study revealed that immunofluorescence on paraffin sections cannot replace immunofluorescence on frozen sections in the assessment of human renal biopsies, and must be interpreted with great caution