Electrical activity following cellular recognition of self and non-self in a sea anemone

The sea anemone Anthopleura elegantissima lives in clonal colonies and possesses a cellular recognition system of remarkable specificity, by which it can recognize members of its own clone; other anemones, including individuals of the same species which are not syngeneic, are attacked. Attack is initiated by contact with a foreign anthozoan and involves the inflation of specialized tentacle-like structures known as acrorhagi, which contain numerous stinging cells. These stinging cells only discharge when the tip of the acrorhagus is in physical contact with the surface of a foreign anthozoan; contact with syngeneic individuals, organisms other than anthozoans and inanimate objects does not elicit discharge. We show here that the recognition of allogeneic tissue is accompanied by a novel form of local electrical activity in the acrorhagus that is usually, but not invariably, followed by nematocyst discharge. This type of electrical activity was not found during contact with syngeneic tissue or inanimate objects and seemed to be a consequence of the recognition of allogeneic surface markers by cells at the tip of the acrorhagus.