CD21 protein, as a receptor for complement C3d and HNRNPU, plays a crucial role in B lymphocyte activation. It forms complexes with CD19, CR2/CD21, CD81 and IFITM1/CD225 and contributes to immune responses. CD21 Protein, Mouse (HEK293, His) is the recombinant mouse-derived CD21 protein, expressed by HEK293 , with C-His labeled tag.