CD179a is an 18 kD Ig V-like protein expressed on pro-B and early pre-B cells. It is a member of the Ig gene superfamily, known as VpreB, VPREB1, and IGVPB. CD179a noncovalently associates with CD179b (lambda5) to form a surrogate light (SL) chain. The SL chain is complexed with membrane bound IgM heavy (microH) chain and CD79a/CD79b heterodimer to form the pre-B-cell receptor (PreBCR) complex. The function of CD179a/CD179b is still under investigation though it has been reported that the pre-BCR complex plays a critical role in B cell development.