Hamster cheek pouch skin, transplanted to the side of an isogenic host's chest wall, retains its immunologically privileged status as evidenced by the prolonged survival of inlaid homografts of ordinary skin.
Various findings sustain the premise that exemption from rejection by otherwise susceptible homografts in both intact pouch tissue and in established pouch skin isografts is due to an impediment in the afferent pathway of the immunologic reflex, i.e., to deficient lymphatic drainage. Although lymphatics were not apparent when dye was injected into pouch skin grafts or into grafts of ordinary skin sustained by them, lymph vessels were readily and consistently revealed by dye injected into intact trunk skin or established isografts of trunk skin. When suspensions of viable lymph node cells from specifically sensitized parental strain donors were injected superficially into either the intact skin or established grafts of normal skin on F1 hybrid hamsters, a striking hypertrophy of the regional lymph nodes occurred, due to graft-versus-host reactivity. However, similar cell suspensions inoculated into intact pouch tissue or into pouch skin grafts on F1 hamsters incited no regional lymphadenopathy, indicating the lack of appropriate pathways to the nodes.
When skin homografts were inlaid eccentrically into pouch skin isografts, so that they were in contact with host skin at one edge, rejection occurred. Furthermore, rejection of long-established intrapouch skin homografts resulted if the hosts received: (a) small homografts of ordinary skin transplanted to conventional beds; (b) suspensions of donor strain pouch skin epidermal cells, injected intracutaneously; (c) lymph node cells from specifically sensitized donors of the same strain, i.e. adoptive immunization; or, (d) if a portion of the target homograft's perimeter was surgically approximated to body skin.
Treatment of normal hamsters with two closely spaced pulses of ALS, although only marginally effective in prolonging the lives of homografts of trunk skin, enabled pouch skin homografts to survive for very long periods. The influence of this brief treatment with immunosuppressant was still demonstrable if challenge of hosts with the weakly immunogenic pouch skin homografts was delayed for 100 days.