The H1.2F3 monoclonal antibody specifically reacts with human CD69, the 27-33 kDA type II transmembrane protein also known as the very early activation antigen （VEA） or the activation inducer molecule （AIM）.
It is expressed as a disulfide-linked dimer on B cells, T cells, NK cells, platelets, eosinophils, and neutrophils.
It increases in expression upon cell activation and seems to serve a role as a signaling receptor.
