Thymocyte proliferation-inducing activity of high molecular weight fraction from the culture supernatant of thymic epithelial cell line established from normal rat thymus.

Precursor T cells originated from bone marrow proliferate, differentiate and maturate (thymic education process) to relatively mature T cells under the influence of thymic epithelial cells (TECs). Thymic hormonal factors (THFs) released from TECs presumably play a pivotal role in the thymic education. The THFs related to the thymocyte differentiation and maturation were carefully examined and some of them identified. However, the relation of THFs with thymocyte proliferation (TPIFs) are poorly understood. Consequently we attempted to study the activities of TPIFs under physiological conditions. In this investigation, we employed a TEC line derived from normal rat thymus, disposable reversed-phase column cartridge for concentrating the culture supernatant of TEC (TECS) and high-performance liquid chromatography. By separating TECS sample with ion exchange chromatography, the thymocyte proliferation-inducing activity (TPIA) was efficiently separated from the thymocyte proliferation-suppressing activity. The TPIA was detected in the fraction with high molecular weight (198 to 310 kDa) by gel filtration chromatography. The TPIA was completely reduced by trypsin digestion, while heat-treatment affected only slightly the TPIA.