Immune defense and biological responses induced by toxics in Annelida

Abstract

The phylum Annelida comprises primitive coelomates that possess specially developed cellular immunity against pathogens. Active phagocytosis by coelomocytes occurs in the struggle against bacteria in Polychaeta and Oligochaeta. Encapsulation plays an important role in defense against parasites, and experimental studies have demonstrated that cooperation between different coelomocyte populations occurs in this process. Spontaneous cytotoxicity of coelomocytes against xenogenic or allogenic cells is analogous with that of vertebrate natural killer cells. Graft rejection is a model for studying the activity of these cells. Accelerated rejection following multiple transplantation reveals that the cellular immune defense system has a short-term memory. In humoral immunity, agglutinins aggregate foreign material and their level is enhanced by antigens; in Annelida, however, no specificity analogous to vertebrate antibodies has been revealed, except for weak specificity of some antigen-binding proteins. Hemolytic substances have been detected, particularly in Oligochaeta, where a fetidin possesses bactericidal activity. Lysozyme and some antibacterial proteins also occur in Polychaeta. Annelida react to physical and chemical insults by various processes. These responses are mainly due to synthesis of stress-induced proteins, inhibition of enzyme activity, and modulation (inhibition or stimulation) of the activity of enzymes involved in the detoxification of xenobiotics. Moreover, these responses frequently differ from those of vertebrates, particularly in terms of the nature of inducers. In other respects, these responses are extremely variable in Annelida, even in closely related species.