Description: The H1.2F3 monoclonal antibody reacts with mouse CD69, also known as very early activation antigen (VEA). CD69 is approximately 35 kDa and is expressed on the surface as a disulfide-linked dimer. While a small subset of lymphocytes in the thymus, spleen and lymph nodes express this antigen, activation of both T and B cells rapidly upregulates the surface expression of CD69, suggesting a role for CD69 in lymphocyte development and activation.