The overall objective of the proposed research is to delineate the mechanism of opsonin-mediated cell recognition of nonself in insects. The hemolymph lectin of the beet armyworm having characteristics similar to those reported for soluble vertebrate lectins, has been demonstrated to e an effective opsonin of fungal cells. Based on prior experiments we believe that when the S. exigua lectin binds to the fungal wall, it undergoes a conformational change, exposing sites which bind to receptors on the hemocyte membrane. Initial experiments will examine the ability of 125I-labeled S. exigua lectin-substrate complexes to bind to hemocyte monolayers. Secondly, S. exigua lectin affinity matrices will be utilized to pluck the receptors from labeled hemocytes and identify the receptor complex present in the hemocyte cell membrane. The data generated form these experiments will provide novel information as to how humoral lectins operate as opsonins or transport molecules in insects. This proposal addresses a fundamental issue in insect immunology. The prevailing belief in the field is that lectins, proteins which recognize and bind specific carbohydrate structures, function as immune surveillance proteins in the primitive insect circulatory system, much as immunoglobulin antibodies recognize and bind specific haptenic structures in the vertebrate circulatory system. The hypothesis being explored in this project is that, once bound, the lectin "opsonizes" the pathogen much as antibodies opsonize bacteria, enabling phagocytic cells of the immune system to recognize the antibody-antigen complex and to engulf and degrade the invading microorganism. The results of this research will expand our understanding of the role of lectins in invertebrate immune responses.
