Identification of the Humoral Lectin Receptor on Insect Hemocytes

提出的研究的总体目标是描述调节素介导的昆虫非自我细胞识别的机制。甜菜粘虫的血淋巴凝集素具有与可溶性脊椎动物凝集素相似的特征，已被证明是一种有效的真菌细胞调理素。基于先前的实验，我们认为当S. exigua凝集素与真菌壁结合时，它会发生构象变化，暴露出与血细胞膜上受体结合的位点。初步实验将检验125i标记的葡萄凝集素-底物复合物与血细胞单层结合的能力。其次，利用紫花葡萄凝集素亲和基质从标记的血细胞中提取受体，并鉴定存在于血细胞细胞膜中的受体复合物。这些实验产生的数据将提供关于体液凝集素如何在昆虫体内作为调理素或运输分子运作的新信息。这一建议解决了昆虫免疫学中的一个基本问题。该领域普遍认为，凝集素是一种识别和结合特定碳水化合物结构的蛋白质，在原始昆虫循环系统中起着免疫监视蛋白的作用，就像免疫球蛋白抗体识别和结合脊椎动物循环系统中的特定半抗原结构一样。这个项目正在探索的假设是，凝集素一旦结合，就会像抗体调理细菌一样“调理”病原体，使免疫系统的吞噬细胞能够识别抗体-抗原复合物，并吞噬和降解入侵的微生物。这项研究的结果将扩大我们对凝集素在无脊椎动物免疫反应中的作用的理解。

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.