Stereological study of splenic tissue compartments in FK506-treated rats.

Model-based stereology was used to study the changes of splenic structure and proportions of splenic tissue compartments in FK506-treated male Wistar rats (0.1 mg/kg three times a week for 14 days). The point-counting method was utilized to study the volume densities of the following tissue compartments: red pulp; white pulp (this compartment was divided in two subcompartments: follicles and periarteriolar lymphocyte sheath); marginal zone; and connective tissue. The following stereological parameters of lymphoid follicles were also determined: areal numerical density (the number of follicles per mm2 of tissue section); the numerical density (number of follicles per mm3 of tissue); and the mean follicle diameter. After FK506 treatment a significant reduction of volume density of white pulp was observed, which was due to the very prominent decline in the amount of periarteriolar lymphocyte sheath, whereby the cellular density of this tissue compartment was decreased. In the marginal zone of FK506-treated spleens the presence of numerous, large, densely packed lymphoblastic cells of very uniform appearance 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 these immunosuppressive agents.