Distribution of dendritic reticulum cells in follicular lymphoma and reactive hyperplasia. Light microscopic identification and general morphology.

Reactive and neoplastic follicles in lymph nodes showing changes of (1) follicular hyperplasia and (2) follicular lymphoma were examined for the presence of dendritic reticulum cells (DRC). These cells could be identified under the light microscope after comparing electron microscopical sections with subsequent 1 micro sections of reactive germinal centres. Quantitative light microscopical evaluation showed that DRC, both mononuclear and binuclear forms, were less numerous in neoplastic follicular structures than in reactive follicles. Before determining the frequency of binucleated DRC in follicular tissue their morphology was studied first in cell suspensions. DRC isolated by enzymatic treatment of tonsils and reactive lymph nodes were morphologically identical and contained one, or at most two, nuclei arranged in a typical doublet formation. Stereological calculations - made on three dimensional models of nuclear complexes prepared from serial tissue sections - indicated that 51 to 68% of DRC in reactive germinal centres were binucleated, whereas in neoplastic follicles this figure is 18 to 23%. The multinucleated giant cell forms of DRC described by others result from complex formation with other DRC or lymphoid cells. The smaller number of DRC and the lower frequency of binucleated DRC in follicular lymphomas suggest that differentiation of DRC from stromal cells is less complete in these neoplasms. The ability to identify DRC reliably by light microscopy offers a new means to define the difference in frequency of DRC. This may be of practical value in distinguishing reactive germinal centres from neoplastic follicles.