Insect Immune Defense System, Part I: Innate Defense Reactions

Abstract

In the strictest sense, invertebrate organisms, including insects, do not possess immune capabilities. Immune response is defined as that response made by the immune system of a vertebrate when invaded by foreign substances or by microorganisms (Alberts et al., 1994). Immune response is anticipatory, meaning that once a vertebrate animal acquires an infection, it is unlikely to develop this same infection again. This is due to the fact that protein molecules called antibodies or immunoglobulins (Ig), which are highly specific for the immunostimulatory molecules produced by the agent that caused the initial infection, can be rapidly generated by memory cells. Memory cells are lymphocytes (white blood cells) that do not actively engage in making a response to a foreign antigen during the primary challenge, but they react readily upon re-exposure of the animal to the same antigen. Invertebrates lack the lymphocytes necessary to produce the antibodies needed for immunological memory and subsequent anticipatory immune response. Thus, to classify invertebrate intrahemocoelic cellular and humoral defense mechanisms as components of an immune defense system is inaccurate. However, this is often done in order to distinguish these activities from other defensive strategies. As examples, in many insects the exoskeleton serves as a highly resistant barrier against the entry of pathogenic organisms; similarly, the behavioral practices of insects (e.g., grooming) can provide significant protection against infection.

“There’s only one principle of war and that’s this. Hit the other fellow, as quick as you can, and as hard as you can, where it hurts him the most when he ain’t lookin. ”

...Sir William Slim, 1956