Fenestration of Nuclei of Lymphocytes

Abstract

The abnormality of the nuclei of some of the lymphocytes in infectious mononucleosis described below was first observed in 1933. Since then I have found it in all of the 12 cases of infectious mononucleosis studied and it has not been observed in any other condition, although differential counts are made on about 50 to 100 bloods a day in the laboratory under my direction and the technicians were asked to look especially for these fenestrations. In 2 or 3 instances fenestrated nuclei were observed before the diagnosis of infectious mononucleosis had been made by other methods, and this diagnosis was later confirmed by finding the typical large lymphocytes, a positive Paul and Bunnell test, and by the clinical course.

The fenestrated nuclei∗ appear at first glance to be nuclei containing multiple nucleoli, but careful inspection shows that in the Wright's stained smear there are actually multiple holes, piercing the nucleus in various directions. In those which are parallel to the light beam through the microscope it is obvious that they are holes; but the majority will, from the laws of chance, not have this direction and their diagonal course through the nucleus gives the appearance of an oval-shaped area of decreased density which may or may not have a clear patch at one end. These may be differentiated from nucleoli by the facts that they are too numerous and that their background is the same color as the rest of the nucleus but paler, while in nucleoli the color is a pure blue with no tinge of red in it.

These fenestrations may be present in the nuclei of either the normal or large lymphocytes but are most often seen in the smallest of the otherwise normal lymphocytes.