Immune CD4⁺ T cells specific for Theileria parva-infected lymphocytes recognize a 24-kilodalton protein

Theileria parva is a protozoan parasite that infects and transforms bovine lymphocytes. Here we report the partial purification of a T. parva-specific protein from infected lymphocytes that is recognized by CD4⁺ parasite- specific T-cell clones derived from immune cattle. T. parva-infected lymphocytes were homogenized in Dulbecco's phosphate-buffered saline in the presence of protease inhibitors. The antigen was purified from a postmicrosomal supernatant by using a combination of DEAE-cellulose chromatography and hydroxylapatite column chromatography. After labelling with ¹²⁵I, the antigen preparation was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and found to contain 8 to 10 proteins. This preparation was subjected to chromatography in phosphate- buffered saline on HPLC TSK-250/125 columns coupled in tandem. A radiolabelled protein of M(r) 24,000 correlated with antigenic activity.