Immunohistochemical determination of growth fractions in human permanent cell lines and lymphoid tumours: a critical comparison of the monoclonal antibodies OKT9 and Ki-67.

OKT9 and Ki-67 monoclonal antibodies have recently been proposed as useful tools for evaluating the growth fraction in malignant tumours, with special reference to non-Hodgkin's lymphomas. In particular, while the former is commonly thought to detect a transferrin receptor present on the cytoplasmic membrane of proliferating cells, the latter recognizes a nuclear antigen, which is expressed in G1, S, G2 and M phase of continuously cycling elements. To further verify their reliability, OKT9 and Ki-67 were applied to seven permanent cell lines (four myeloid and three B-lymphoblastoid) and 100 lymphoid tumours (70 non-Hodgkin's and 30 Hodgkin's lymphomas) phenotypically characterized on frozen sections. The results obtained showed that OKT9 and Ki-67 cannot be employed as equivalent means in assessing the growth fraction. In fact, OKT9 is directed to a transferrin receptor which is not only expressed by proliferating cells, but also by some resting elements. On the other hand, Ki-67 provides a nuclear, easily detectable positivity which is restricted to proliferating cells only. Therefore, it seems to represent the only monoclonal which can confidently be employed in the assessment of the growth fraction. Furthermore, the present study underlines that the immunocytochemical analysis of the proliferation rate in tumours gives similar information to the radionucleide uptake assay, while it represents a more sensitive method than the cytofluorimetric evaluation of the DNA content.