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Comparison of Ki-67 equivalent antibodies

¹ Department of Pathology, Vest-Agder Central Hospital, N-4604 Kristiansand, Norway
² Department of Laboratory Medicine and Pathology, Norwegian University of Science and Technology, Trondheim University Hospital, N-7006 Trondheim, Norway

Correspondence to:
Dr C F Lindboe, Department of Pathology, Vest-Agder Central Hospital, N-4604 Kristiansand, Norway;
c.lindboe{at}c2i.net
ABSTRACT
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.

Keywords: Ki-67; proliferative activity; immunohistochemistry

Abbreviations: LI, labelling index; PNCA, proliferating cell nuclear antigen

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