Short-term immunoisolation of incompatible xenografts in a snail, Biomphalaria glabrata

Hearts of the snails Physa virgata and Biomphalaria glabrata were implanted into the hemocoel of B. glabrata. Implants either were microencapsulated in 2.5% agarose or were unencapsulated. Unencapsulated xenografts from P. virgata underwent complete necrosis within 3 days post-implantation (DPI), whereas allografts were still alive at 7 DPI. In the case of microencapsulated implants, both allografts and xenografts were alive at 3 DPI, showing 4.8 and 14.9% pyknosis among myofiber nuclei, respectively. These results suggest that direct cytotoxicity by hemocytes, rather than toxic plasma factors or donor-recipient physiological incompatibility, is responsible for rapid xenograft death. However, both types of microencapsulated grafts were necrotic at 7 DPI. This necrosis may have resulted from oxygen deprivation brought about both by the agarose and by the heterotopic implantation site, inasmuch as microencapsulated allografts and xenografts cultured in saline for 7 days showed only 1.98 and 30% pyknosis, respectively.