Comparison of Ki-67 equivalent antibodies.

AIMS To compare commercially available Ki-67 equivalent antibodies with regard to qualitative and quantitative immunohistochemical staining characteristics. METHODS The following antibodies were used: monoclonal MIB-1 (Immunotech), monoclonal MM1 (Novocastra), polyclonal NCL-Ki-67p (Novocastra), and polyclonal Rah Ki-67 (Dako). All immunostainings were evaluated in squamous epithelium from formalin fixed and paraffin wax embedded pharyngeal tonsils. Labelling indices (LIs) were recorded twice to test their reproducibility. RESULTS By application of all four antibodies the nuclear staining could be either diffuse, granular, or a combination of both (classified as granular in this study). The diffuse pattern generally showed a strong or moderate staining intensity, whereas the granular pattern displayed a continuum from strong to very weak, making it difficult to discriminate between positive and negative nuclei. The diffuse staining pattern was seen in approximately 59% of the nuclei with the MIB-1 antibody and in 35-45% when the other antibodies were used. The following mean LIs were recorded: MIB-1, 31%; NCL-Ki-67p, 21%; Rah Ki-67, 17%; and MM1, 14%. The reproducibility was excellent for all four antibodies, with the mean of differences between the two runs of counts ranging from 1.1% to 1.5%. CONCLUSIONS The four tested Ki-67 equivalent antibodies revealed differences in qualitative and quantitative staining characteristics, which resulted in considerable variations in registered LIs. The MIB-1 antibody appears to have a higher sensitivity for detecting the Ki-67 antigen than the other three tested antibodies. These differences are important to consider when proliferative activity is determined by the Ki-67 LI.