CD179a, also known as VpreB, is an 18 kD member of the Ig superfamily, with an Ig V-like domain structure (that lacks the beta strand of a typical V domain). CD179a associates with CD179b to form a surrogate light (SL) chain, which associates with the IgM heavy chain and the 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 deficiency of CD179a and/or CD179b impairs the maturation of the B cell precursors beyond the pre-B cell stage.