The antibody recognizes CD7, a human T and NK lymphocyte antigen of 40 kDa. The CD7 antigen is expressed throughout T lymphocyte differentiation, and is present on 85% to 90% of peripheral blood T lymphocytes. In normal individuals, the CD7 antibody reacts with all CD8+ lymphocytes, approximately 90% of CD4+ lymphocytes, and most NK lymphocytes. CD7 is weakly reactive with monocytes and does not react with granulocytes or B lymphocytes. It is expressed on 50% of thymocytes in suspension. In leukemias, the CD7 antigen is present on the majority of T lymphoid lineages.