This rabbit monoclonal antibody reacts with the intracytoplasmic portion of the CD3 antigen expressed by T-cells. It stains human T-cells in both the cortex and medulla of the thymus and in peripheral lymphoid tissues. It does not react with B-cells, monocytes, granulocytes and platelets. CD3 is regarded as a reliable pan T-cell antibody used in the immunophenotyping of T-cell lymphomas in paraffin sections. Most T-cell lymphomas show positivity for CD3.