Clone REAL405 recognizes both alloantigeneic forms of the mouse CD8b antigen, a single-pass type I membrane protein also known as lymphocyte antigen 3 (Ly-3 or Lyt-3). The CD8 molecule is composed of two distinct polypeptide chains that pair on the cell surface either as a CD8aa homodimer or as a CD8ab heterodimer. These forms of the CD8 molecule are differentially expressed on functionally distinct CD8
+ lymphocyte subsets. The CD8ab heterodimer is expressed on cytotoxic T cells and thymocytes.