The function of ENSG00000117322 (CR2, complement C3d receptor 2) is as follows. Serves as a receptor for various ligands including complement component CD3d, HNRNPU OR IFNA1 (PubMed:1849076, PubMed:21527715, PubMed:7753047). When C3d is bound to antigens, attaches to C3d on B- cell surface and thereby facilitates the recognition and uptake of antigens by B-cells (PubMed:21527715). This interaction enhances B-cell activation and subsequent immune responses. Forms a complex with several partners on the surface of B-cells including CD19, FCRL5 and CD81, to form the B-cell coreceptor complex that plays a crucial role in B-cell activation and signaling (PubMed:1383329, PubMed:30107486). Also induces specific intracellular signaling separately from the BCR and CD19 by activating the tyrosine kinase SRC, which then phosphorylates nucleolin/NCL and triggers AKT and GSK3 kinase activities in a SYK/CD19-independent manner (PubMed:12938232). Acts as a ligand for CD23 (FcepsilonRII), a low-affinity receptor for IgE, which is expressed on B-cells and other immune cells, and thus participates in the regulation of IgE production (PubMed:1386409). {ECO:0000269|PubMed:12938232, ECO:0000269|PubMed:1383329, ECO:0000269|PubMed:1386409, ECO:0000269|PubMed:1849076, ECO:0000269|PubMed:21527715, ECO:0000269|PubMed:30107486, ECO:0000269|PubMed:7753047}. (Microbial infection) Acts as a receptor for Epstein-Barr virus. .