STEREOLOGICAL STUDY OF SPLENIC TISSUE COMPARTMENTS IN FK506-TREATED RATS

Model-based stereology was used to study the changes of splenic struct ure and proportions of splenic tissue compartments in FK506-treated ma le Wistar rats (0.1 mg/kg three times a week for 14 days). The point-c ounting method was utilized to study the volume densities of the follo wing tissue compartments: red pulp; white pulp (this compartment was d ivided in two subcompartments: follicles and periarteriolar lymphocyte sheath); marginal zone; and connective tissue. The following stereolo gical parameters of lymphoid follicles were also determined: areal num erical density (the number of follicles per mm(2) of tissue section); the numerical density (number of follicles per mm(3) of tissue); and t he mean follicle diameter. After FK506 treatment a significant reducti on of volume density of white pulp was observed, which was due to the very prominent decline in the amount of periarteriolar lymphocyte shea th, whereby the cellular density of this tissue compartment was decrea sed. In the marginal zone of FK506-treated spleens the presence of num erous, large, densely packed lymphoblastic cells of very uniform appea rance was registered. These observations are in very good keeping with the changes of splenic morphology registered in cyclosporin A-treated rats, which further documents the parallelism in actions between thes e immunosuppressive agents.