Background：CD5 is a 67 kD protein, also known as Lyt-1, Ly-1, T1, Tp67, or Ly-12. It is a member of the scavenger receptor cysteine-rich protein superfamily （SRCR） and primarily expressed on thymocytes, T cells, and B-1 cells. Although mature a/b T cells express high levels of CD5, very few gamma/delta T cells express this antigen. The interaction of CD5 with CD72, gp35-37, TCR, or BCR is involved in T and B cell activation.
