ALLOIMMUNE MATURATION IN THE CORAL STYLOPHORA-PISTILLATA IS ACHIEVED THROUGH 3 DISTINCTIVE STAGES, 4 MONTHS POST-METAMORPHOSIS

Adult colonies of the reef-building coral Stylophora pistillata discri minate precisely between 'self' and 'non-self' attributes, and respond selectively against specific allogeneic challenges. We studied the on togeny of these allospecific responses on newly settled polyps by esta blishing allogeneic contacts within groups of 2-6 siblings or non-rela ted offspring. Interactions were observed for up to 8 months. Three ty pes of response, depending on the age of the interacting partners, wer e documented. The first was tissue fusion and the formation of a stabl e chimera, observed in partners less than 2 months old. The second was observed in contacts of partners 2-4 months old. It started with tiss ue fusion and transitory chimera since separation of the chimera partn ers or polyp death resulted when the oldest partner in the chimera rea ched the age of 4 months. The third type was the regular histoincompat ibility response, as documented in allogeneic interactions of adult co lonies, recorded here in all encounters with S. pistillata partners ov er 4 months old. Maturation of allorecognition in this species was the refore achieved through three time-dependent stages, 4 months followin g metamorphosis. Combinations of siblings or genetically unrelated par tners did not affect the results. We propose that the coral alloimmune maturation system may be used as a new evolutionary model scheme for studying tissue transplantation and tolerance.