Mouse CD79b (Igbeta chain) is a 35-40kD transmembrane protein that forms a heterodimer with CD79a (30-35 kD, Ig alpha chain).The CD79b and CD79a hererodimers are associated with surface IgM to form the B-cell receptor (BCR) that is necessary for signal transduction via the BCR in mature B cells.CD79b participates signal transduction involved in the development of B cells as well. It was reported that association between CD79b/CD79a with IgM is essential in inducing both the transition from progenitor to precursor B cells and subsequent allelic exclusion.Igbeta knockout mice had a complete block in B cell development at the immature CD43+B220+ stage. The HM79b-12 react with an extracellular epitope of CD79b or Ig beta.