Cell adhesion and the immune system: A case study using earthworms

In the earthworm's immune system, cell adhesion, which occurs by putative r eceptors on leukocytes, is essential after recognition of self vs. non-self . Confrontation with foreign antigens is a normal event in the environment, replete with microbial pathogens that pose a threat to survival. To better understand what happens when an effector cell first recognizes a foreign t arget followed by its adhesion to it, isolated leukocytes, in sufficient qu antities to be subjected to various analyses, have been extremely beneficia l. In vitro approaches when accompanied by biochemical, immunological, and molecular technologies, have opened up new vistas concerning the immune res ponse of earthworms and other invertebrates. The most recent discovery incl udes the preliminary identification of cell differentiation (CD) markers th at play vital roles in recognitive and adhesive events. Certain leukocyte e ffecters show characteristics of natural killer (NK) cells that may act dif ferently depending upon their source, whether autogeneic, allogeneic, xenog eneic, or expressed under normal or varying environmental conditions includ ing exposure to xenobiotics. At the level of earthworm evolution, there is apparently a dissociation of phagocytosis from the process of killing by NK -like effecters. There are at least three future challenges. First, it is e ssential to determine the precise nature of the CD markers with respect to their molecular structure. Second, once their molecular and biochemical cha racteristics have been defined, the role of these markers in cellular and h umoral mechanisms must be clarified in order to define effector cell produc ts and resulting immune responses. Third, there is a need to differentiate between the several lytic factors that have been found in earthworms with r espect to molecular structure, and biochemical and functional characterizat ion. Microsc. Res. Tech. 44:237-253, 1999. (C) 1999 Wiley-Liss, Inc.