The A20 monoclonal antibody reacts with the leukocytes of the CD45.1-expressing mouse strains (DA, SJL/J, RIII, and STS/A). It does not cross-react with cells that express CD45.2.

The CD45 molecule is a member of the Protein Tyrosine Phosphatase (PTP) family, because its intracellular region contains two PTP domains. The extracellular region’s variability is caused by different levels of glycosylation, and the splicing of the 4, 5, and 6 exons. The isoforms found in the mouse strains depend on the activation state, maturation stage and cell type, and are very important in B and T lymphocytes antigen receptor signal transduction.

The A20 antibody inhibits some of the B lymphocytes responses, from CD45.1-expressing mice, to lipopolysaccharides and antigens.