Caterpillars of silkworms and other moths are known to produce peptides (cytokines) that can cause larval paralysis. It is speculated that these peptides may serve as a partial defense against parasitoids. The levels of paralytic peptide that can be isolated from the hemolymph of a caterpillar are many times that needed to induce paralysis. How can the caterpillar avoid the paralytic effects of its own peptides?
The peptide circulates in the hemolymph in an inactive form. It can be converted to a modified “paralytic” form by serine proteases that respond to damage to the caterpillar cuticle and loss of hemolymph. The activated protein has a number of biological effects such as paralysis accompanying muscle contraction and changing the shape of hemocytes as part of the immune defensive response of the caterpillar.
Caterpillars are important models for the study of immune response. Knowing how caterpillars fight infections could lead to new methods for fighting human infections.
Soon-Duck Ha, Shinji Nagata, Akinori Suzuki, Hiroshi Karaoke. Isolation and structure determination of a paralytic peptide from the hemolymph of the silkworm, Bombyx mori. Peptides. Volume 20, Issue 5, June 1999, Pages 561-568.