HETEROTOPIC HEART TRANSPLANTS IN BIOMPHALARIA GLABRATA (MOLLUSCA: PULMONATA): FATE OF XENOGRAFTS FROM SEVEN PULMONATE GENERA

Hearts were implanted heterotopically into the hemocoel of the snail Biomphalaria glabrata from members of 7 pulmonate genera: Bulinus truncatus, Drepanotrema kermatoides, Helisoma trivolvis, Physa virgata, Planorbis atticus, Pseudosuccinea columella, and Segmentina hemisphaerula. Hearts from H. trivolvis withstood an initial host hemocytic response and continued to contract for 6 months. However, xenografts from the other 6 species were infiltrated and encapsulated by host hemocytes and underwent destruction between 1 and 15 days post-implantation. Graft destruction may have involved both immunological rejection and physiological incompatibility with recipient plasma, but the former was probably more important because (1) necrosis of heart myofibers occurred rapidly and only following hemocytic infiltration, and (2) some donor hearts possessed mostly euchromatic nuclei and continued to contract for up to 2 weeks when cultured in isotonic saline. Additional key words: organ transplantation, histocompatibility Recent studies have demonstrated long-term survival of both allografts and xenografts in the freshwater pulmonate snail Biomphalaria glabrata (SAY). Specifically, when heart allografts or congeneric xenografts are implanted heterotopically into the hemocoel, they maintain histological integrity, high levels of intracellular glycogen, and myogenic contraction for 6 months, despite undergoing a recipient hemocytic response and some pathological alterations (Sullivan et al. 1992, 1993). As discussed previously, whether such long-term graft survival represents true acceptance or a form of chronic rejection is not known (Sullivan et al. 1993). Although xenografts from congeneric donors survived in Biomphalaria glabrata, we predicted that grafts from more distantly related donors eventually would undergo destruction, due to immunological rejection, physiological incompatibility, or both. To test this hypothesis, we implanted individuals of Biomphalaria glabrata with hearts of donors from 7 other freshwater pulmonate snail genera. We report (1) nearly uniformly rapid necrosis of grafts from all donors, with one interesting exception, and (2) evidence that graft necrosis results primarily from immunological rejection, rather than from physiological incompatibility with recipient plasma. a Author for correspondence and reprint requests. Methods Snails. As in previous investigations, recipients were laboratory-reared specimens of the NIH albino stock (Newton 1955) of Biomphalaria glabrata, 1215 mm in shell diameter. The following 7 donors were used: Bulinus truncatus (AUDOUIN), Drepanotrema kermatoides (D'ORBIGNY), Helisoma trivolvis (SAY), Physa virgata (GOULD), Planorbis atticus BOURGUIGNAT, Pseudosuccinea columella (SAY), and Segmentina hemisphaerula (BENSON). Source of the snails and their classification according to Vaught (1989) is shown in Table 1. (For alternative taxonomic schemes, see Malek & Cheng 1974; Hubendick 1978.) Donor species were selected on the basis of taxonomic differences from the recipient, and ease of procurement from local collection sites or generous colleagues (see Acknowledgments). Donors were reared in the laboratory from eggs in aerated aquariums or covered jars at 26-27? C and were fed either fresh or boiled leaves of Romaine lettuce. Donor shell diameters or shell heights were 5.0-5.2 mm for D. kermatoides, 6.0-6.3 mm for S. hemisphaerula, and 6.5-8.0 mm for the remaining species. Implantation technique. Previously described methods were used for dissecting hearts from donors and implanting them into a hemolymph sinus medial to the recipient's intestine and between the albumin and digestive glands on the left side (Sullivan et al. This content downloaded from 157.55.39.254 on Mon, 05 Sep 2016 04:56:55 UTC All use subject to http://about.jstor.org/terms Sullivan, Brammer, Hargraves, & Owens Table 1. Abbreviated classification of donor and recipient snails.1,2 All are pulmonate gastropods in the order Basommatophora. Superfamily Lymnaeoidea Family Lymnaeidae Pseudosuccinea columella (Iowa City, Iowa) Superfamily Physoidea Family Physidae Physa virgata (Beaumont, Texas) Superfamily Planorboidea Family Planorbidae Subfamily Planorbinae