IMMUNOCOMPETENT CELLS ARE RESPONSIBLE FOR REJECTION OF INCOMPATIBLE XENOGENEIC GRAFTS IN LINEUS (INVERTEBRATA, NEMERTEA)

Abstract

Previous studies have shown that Lineus exhibits a highly discriminating xenoimmunity with a species-specific immune memory component. To learn more about the immune response to incompatible xenogeneic grafts in Lineus, we have studied the survival of transplants from donors of a third species (Lineus ruber) onto bi-specific (Lineus sanguineus-Lineus lacteus) chimeric recipients.

Antecerebral ends from L. ruber donors were grafted onto chimeric worms previously constructed from a L. sanguineus anterior component and a L. lacteus posterior component. When the intestinal segment of the chimeras consisted exclusively of L. lacteus tissues, the survival times of the grafts were in accordance with those characteristic of the interspecific combination L. ruber-L. lacteus. On the other hand, when at least part of the intestinal segment was from L. sanguineus, the graft survival times were in accordance with those characteristic of the combination L. ruber-L. sanguineus.

Similar grafts (antecerebral ends from L. ruber) onto bispecific chimeras constructed from a L. lacteus anterior component and a L. sanguineus posterior component had survival times characteristic for the interspecific combination L. ruber-L. sanguineus, i.e., the combination graft/posterior component of the chimera.

The present experimental design shows clearly that the survival of incompatible xenogeneic grafts in Lineus chimeras is dependent only on the compatibility of cells from the intestinal segment of the recipient's body and those of the antecerebral graft. Thus, the immunocompetent anatomical region of Lineus is the intestinal segment, where the cells arise that are responsible for the rejection of the distant antecerebral end graft. These immunocompetent cells are very likely mobile cells of the nemertine blood, with recognition and cytotoxic functions. Lineus is now one of the few invertebrates in which the existence of a cell-mediated immune response to incompatible grafts has been clearly demonstrated.