The function of CD79B (CD79b molecule, Ensembl gene identifier ENSG00000007312) is as follows. Required in cooperation with CD79A for initiation of the signal transduction cascade activated by the B-cell antigen receptor complex (BCR) which leads to internalization of the complex, trafficking to late endosomes and antigen presentation. Enhances phosphorylation of CD79A, possibly by recruiting kinases which phosphorylate CD79A or by recruiting proteins which bind to CD79A and protect it from dephosphorylation. {ECO:0000269|PubMed:12097390, ECO:0000269|PubMed:8617796, ECO:0000269|PubMed:9057631}.