Identification and partial purification of "transcortin"-like protein within human lymphocytes.

We have detected and localized in situ lymphocyte proteins with antigenic determinants similar to those of the cortisol-binding globulin of human plasma. All lymphocyte fractions, obtained by differential centrifugation and ammonium sulfate fractionations exhibited cortisol-binding capacities and were recognized by transcortin-specific antibody, Inasmuch as the 40 to 65% ammonium sulfate fraction of the 105,000 x g lymphocyte cytosol accounted for over 90% of the total binding capacity of the cell, this fraction was further purified by the procedure employed for the purification of plasma transcortin. These procedures yielded a protein with about 20% the cortisol-binding capacity of transcortin, migrated more rapidly than transcortin in disc acrylamide electrophoretic systems, and formed a line of identity with transcortin when treated with transcortinspecific antibody. Fluorescein-labeled transcortin antibody applied to sectioned lymphocytes showed almost exclusive cytoplasmic localization of transcortin-like protein. These results show for the first time the existence of cortisolbinding proteins within the human lymphocyte antigenically identical with transcortin.