Comparison of immunofluorescent findings in kidney after snap-freezing and formalin fixation

Two types of tissue preparation for immunofluorescent staining were compared with sections of the same kidney. In one, formalin-fixed paraffin-embedded kidney sections were incubated with pronase (IF-PRON). The optimal pronase exposure for bright, specific IF and a mild background IF, suitable for the whole set of antisera was determined (pronase 0.75 g/l of Tris buffer for 60 min) and this was used for the subsequent steps of the study. Snap-frozen sections were also stained (IF-FROZ). Positive and negative cases, IF intensity, distribution and location in IgA nephropathy, membranous nephropathy, proliferative lupus nephritis were compared by the 2 methods. The main antigens for each disease were adequately revealed by IF-PRON, so that a correct diagnosis was possible in all cases. IF-PRON was also applied to sections before and after prolonged storage of blocks in the files, to see whether or not retrospective analysis is possible. Only minor differences were found between the 2 series of sections. Finally, the exposure of the sections to the continuous fluorescent light showed that IF fading was less in fixed sections. We conclude that IF-PRON is a reliable method for renal pathology with some advantages over the IF-FROZ.