Monoclonal antibodies OKT 11 and OKT 11A have pan‐T reactivity and block sheep erythrocyte “receptors”

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Abstract
Monoclonal antibodies OKT11 (γ1) and OKT11A (γ2) are described and appear to have similar binding specificities. They bind, in immunofluorescence, with >95% of infant thymocytes, staining both cortical and medullary cells, 65‐80% of blood lymphocytes and selectively stain the T cell‐dependent paracortical areas of tonsil. A small proportion (9‐12%) of bone marrow lymphocytes stain, but this population excludes the terminal transferase‐positive cells. Both the γ1 and γ2 antibodies stain the surface membrane Ig‐negative lymphocytes in blood and tonsil and are able to block sheep E rosette formation (to normal or leukemic T cells). In contrast, other monoclonal anti‐T reagents tested (OKT1, OKT3, OKT4, OKT6, OKT8, OKT9, OKT10) did not block E rosette formation. E rosette formation and OKT11 binding are coincident on T‐ALL cell lines and both are trypsin‐sensitive. In a series of 145 leukemias and 26 leukemic cell lines investigated, only leukemias with a T cell phenotype including E rosette positivity were reactive with OKT11 and OKT11A. OKT11A binds to a polypeptide of approximately 50000 molecular weight on thymic lymphocytes. This structure may carry the recognition site for sheep erythrocytes. These antibodies provide additional useful markers for T cell analysis and are of potential therapeutic value.