Humoral mechanisms in the immune response of insects to larvae of Hymenolepis diminuta (Cestoda).

Previous work has shown that larvae of Hymenolepis diminuta are not encapsulated by the haemocytes of the locust, Schistocerca gregaria, but are encapsulated by haemocytes of the cockroach, Periplaneta americana. The specificity of the cellular immune response in vivo, and of the agglutinating activity of the sera against vertebrate erythrocytes in vitro, is known to differ between the two species of insect. Accordingly, the sera of each of these species was tested for its agglutinating activity in vitro against a pure suspension of a known number of freshly-hatched oncospheres of H. diminuta; it was found that serum of P. americana strongly agglutinated oncospheres while the serum of S. gregaria had no effect. The agglutinating activity of cockroach serum was only partially removed by preadsorption with either human, rat or rabbit erythrocytes, all of which are strongly agglutinated by the serum. Although the function in vivo of this agglutinating activity directed against oncospheres is not known, it is suggested that this observation--that both the haemocytes and serum of one insect species respond to the parasite whereas the serum and haemocytes of another species apparently do not--may be of some relevance to the immune recognition mechanisms of insects.