Abstract

Nucleolar organizer regions (NORs) are loops of DNA which occur in the nucleoli of cells which possess ribosomal RNA genes. The numbers and areas of NORs have been thought to be related to cellular activities. We aimed to investigate the direct relationship between the parameters of AgNORs and cellular proliferative activity using immunohistochemical method with the monoclonal antibody Ki-67, which demonstrates proliferating nuclei. The sequential technique for the simultaneous Ki-67 immunostaining and NOR staining was applied to the same slides of a series of non-Hodgkin's lymphomas (NHL) of the low, intermediate, and high grade type. The number of AgNOR per cell was counted and mean NOR percentage nuclear area (NPNA) was measured by morphometry in both the Ki-67 positive and Ki-67 negative nuclei. The increased immunoreactivity for Ki-67 was found in the high grade than in the low grade non-Hodgkin's lymphoma. This was reflected in the two areas of the palatine tonsils and lymph nodes, the positive cell counts being higher in the follicle center nuclei than in those in the interfollicular compartment. In general the numbers and NPNA of AgNORs were higher in the Ki-67 positive nuclei than in those lacking the antigen in malignant lymphomas as well as in control. The AgNORs numbers and NPNA in controls were the highest in the Ki-67 positive cells in the follicular area and the lowest in the Ki-67 negative cells in the perifollicular area. In malignant lymphomas the numbers and NPNA of AgNORs tended to increase in proportion to their grade in both the Ki-67 positive and negative cells. The numbers of AgNORs of the high grade and the NPNA of the intermediate and the high grade were significantly higher in Ki-67 positive cells than in Ki-67 negative ones. With this double staining method it was now possible to confirm that numbers and NPNA of AgNORs were directly related to the cellular proliferative activity. In maligant lymphoma, among the several parameters of the AgNORs, NPNA in Ki-67 positive cells is proposed to be the most useful marker in determining the prognosis of the patient.

• Keywords: AgNOR;Ki-67;Proliferative activity;NOR percentage nuclear area