Characteristics of Cell-Mediated Immunity and Memory in Annelids

Abstract

To search for the phylogenesis of foreign tissue graft rejection we have utilized the common garden earthworm extensively. Whereas earthworms never destroy self-tissue or autografts, they are fully capable of rejecting foreign or not-self tissue allografts (1–5) or xenografts (6). At 15°C, single first-set xenografts exchanged between Lumbricus terrestris and Eisenia foetidaare destroyed at approximately 25–35 days. After a first-set graft is destroyed at 15°C, immunologic memory is demonstrable by regrafting the hosts with a second transplant from the original donor of the first-graft. Both positive and negative memory are demonstrable. Positive memory occurs when second-set transplants are rejected significantly faster than first-sets. By contrast, a lesser percentage of worms have grafts that show prolonged survival indicating negative memory. However, if repeat second-sets are performed at 15°C, five days after transplanting a first-set, during the induction phase of the immune response, there is no dissociation into positive and negative memory. Instead, both first- and second-set grafts are destroyed faster than a single graft (7). It appears therefore that at the evolutionary level of annelid worms, foreign transplant rejection is specific and the mechanism includes a memory component. Memory is one characteristic of adaptive immunity as defined for vertebrates (8).