Recognition of self from non-self in crustaceans

Abstract

THE immune response of vertebrate species seems initially to involve recognition events between immunogenic molecules and specific lymphocyte receptors. These recognition events subsequently result in amplification steps including, in many cases, increases in cells capable of producing humoral antibodies or participating in cell mediated reactions¹. Since invertebrates apparently cannot make humoral antibodies^2,3 but can reject allografts^4,5 it seems appropriate to inquire if such animals have receptors capable of discriminating self from non-self. The similarities between antigen receptors and humoral antibodies in vertebrates^6,7 serve as additional reasons for investigating recognition mechanisms in invertebrates. Although sufficient data exist to indicate that the lectin-like agglutinins present in haemolymph can function as opsonins for foreign erythrocytes in certain invertebrates⁸, considerations of foreignness of protein molecules are not as definitive. Certain crustaceans, such as crayfish⁹ and lobsters¹⁰, can readily clear certain mammalian serum albumins from the circulation but little is known of the specificity of this elimination. We have investigated whether crustaceans possess recognition molecules (referred to as receptors) enabling them to recognise various proteins as foreign and to eliminate these proteins from the circulation. The basic premise was that if such receptors are present, regardless of their location (cell-bound or free), they should be of finite number (and thus saturable) and have some discernable degree of specificity.