Induction of specific inhibition of alloreactivity in beagle dogs by intrathymic injection of donor splenocytes

The aim of this study was to investigate whether intrathymic injection (ITI) of donor splenocytes in dogs might lead to specific immunomodulation as assessed by mixed lymphocyte culture (MLC) tests. Two groups of five beagles each were used. Group 1 contained animals that were 2 years old, group 2 consisted of animals that were 6 months old. One animal was splenectomized per experimental group and 1 x 10⁹ splenocytes were injected into the thymic lobes or thymic remnant of the four remaining dogs. On the day of ITI the dogs were treated subcutaneously with a single dose of 2 ml/kg antilymphocyte serum (ALS). In group 1 the thymus of all dogs was found to be atrophic. ITI in this group did not result in a decreased immunoreactivity but rather in an enhanced immune response. In group 2 the thymus was still clearly present and ITI was easy to perform. ITI induced a significant reduction of specific MLC reactivity at 1 week after treatment. The effect was transient and not significantly further diminished at week 2. These results indicate that ITI is a technically feasible procedure in a preclinical animal model. It may induce temporary sensitization as well as immunosuppression, possibly depending on the age of the recipient.