Chronic skin graft rejection in the urodela. I. A comparative study of first‐ and second‐set allograft reactions

Unlike acute skin allograft reactions observed in most randomly breeding ectothermic and endothermic vertebrates, a basic pattern of intermediate to prolonged chronic skin graft rejection characterized the alloimmune response of representatives of at least five genera of salamanders from three different families (Salamandridae, Ambystomatidae, and Proteidae). First‐set median survival times (MST's) ranged from 33 to 55 days at 25°C. Individual zero end points (total melanophore destruction) occurred between 17 and 120 days. Several grafts appeared to have survived indefinitely (> 300 days) with full to partial viability. MST's of second‐set grafts were significantly shorter than first‐set MST's for all salamanders except Ambystoma tigrinum. For this species, the small sample of seven repeat grafts all exhibited either prolonged survival vis ‐ a ‐ vis first‐set grafts or were destroyed well within the range of first‐set rejections. About 25% of the combined individual Taricha and Necturus repeat grafts were completely destroyed at the same postoperative time as or significantly later than first‐set grafts from the same donor. Only curtailed survival of Cynops second‐set grafts was noted. When the post transplantation period was resolved into a latent phase and a rejection phase, the curtailed survival of 50% of the Traricha and 60% of the Cynops second‐set grafts was attributable solely ot a comparatively shorter latent period. The curtailed zero end points of other Taricha repeat grafts resulted from both shorter latent and shorter rejection intervals. The overall prolonged second‐set survival noted for some Taricha allografts was referable only to longer rejection phases; the latent phases for these repeat grafts were either shorter than or similar to those of the corresponding primary grafts.