Transplantation Immunity in Arthropods: Is Immunorecognition Merely Wound-Healing?

Abstract

An animal such as an arthropod, whose means of support is carried externally to the soft tissues and whose blood circulates through large haemocoelic spaces which are in intimate contact with the cuticle, has a lot to lose if its cuticle is punctured and wounded. It is of prime importance that the wound is plugged immediately, in order to prevent haemolymph leakage and microbial invasion and, indirectly, to restore the integrity of the mechanical support system. As long as the surfaces lining the haemocoele are intact there is little or no adhesion of haemocytes to them; the few haemocytes which are observed adhering to the surfaces of tissues [1] are perhaps merely carrying out a house-keeping role in responding to small molecular irregularities, an argument which has also been used for the primary phagocytic cells of mammals, the neutrophil granulocyte. Any alteration in the tissue surface, whether by mutation [50] or by physical damage [55] will provoke a haemocytic “wound healing” response during which haemocytes aggregate around the altered region. Thus, any transplant or parasite which comes into contract with the haemolymph will be treated as damaged “self” and will stimulate a comparable reaction; the end result of the haemocytic encapsulation or aggregation process, wheather in response to wounds or to transplants, would be to produce a surface with properties similae to intact self (see Sect. 2.1.1). Such a system will be capable of different degrees of response in that more severe damage will produce a greater response and transplants whose surface properties differ widely from self will be more provocative.