血影蛋白（Spectrin），一种细胞结构蛋白，大多位于红血球细胞膜内侧，是红血球骨架的主要成分。血影蛋白在整个细胞膜内侧形成可变形的架构，以维持红血球的双凹圆盘构造。它是一种长且具有伸缩性的纤维状蛋白，长约100nm，由两条单体：αI、βI先平行排列结合成二聚体，两个二聚体再以头对头的方式连接成200nm长的四聚体。5到6个四聚体的尾端透过protein4.1、protein4.2、protein4.9、肌动蛋白（actin）、锚定蛋白（ankyrin）等等蛋白质的帮助下，固定在某些跨膜蛋白（intergral membrane proteins）上。

Spectrin is a cytoskeletal protein that lines the intracellular side of the plasma membrane in eukaryotic cells. Spectrin forms pentagonal or hexagonal arrangements, forming a scaffolding and playing an important role in maintenance of plasma membrane integrity and cytoskeletal structure. The hexagonal arrangements are formed by tetramers of spectrin subunits associating with short actin filaments at either end of the tetramer. These short actin filaments act as junctional complexes allowing the formation of the hexagonal mesh. The protein is named spectrin since it was first isolated as a major protein component of human red blood cells which had been treated with mild detergents; the detergents lysed the cells and the hemoglobin and other cytoplasmic components were washed out. In the light microscope the basic shape of the red blood cell could still be seen as the spectrin containing submembranous cytoskeleton preserved the shape of the cell in outline. This became known as a red blood cell "ghost" (spectre), and so the major protein of the ghost was named spectrin.