Immunosuppressive factor from liver and its influence on T cell development

Immunosuppressive factor from liver induces apoptosis in thymoma EL-4 cells but not normal MHC class II-specific T lymphocytes

An endogenously produced immunosuppressive factor (ISFnp, immunosuppressive factor-neutral protein), inducing a decrease in viability of thymoma EL-4 cells in vitro, was isolated from murine liver using ion exchange, gel filtration and hydrogen-bonding chromatography. Polyclonal rabbit antibodies against this factor were developed and attached to periodate-activated Sepharose CL-6B. The immunoaffine sorbent obtained significantly depleted the biological activity of ISFnp from tested fractions. The factor shows liver-specific location, an M(r) of about 70-80 kDa and consists of 2 subunits (40 and 42 kDa) as determined by SDS-PAGE and Western blotting. ISFnp induced DNA degradation in EL-4 cells similar to the cleavage of DNA onto olygonucleosomal fragments in dexamethasone-treated thymocytes. This DNA degradation preceded lysis of thymoma cells, suggesting an induction of apoptosis in ISFnp-treated EL-4 cells. Addition of the factor into primary mixed lymphocyte culture (MLC) strongly inhibited proliferative response but failed to induce any decrease in the ability of normal MHC class II-specific alloreactive cells to respond in the secondary MLC. Moreover, addition of ISFnp into primary MLC on the peak of proliferative response resulted in augmentation of secondary responses of primed cells as compared with the same quantities of primed cells from untreated cultures. These results suggest a possible role of liver both in deletion of transformed clones of T lymphocytes and formation of allospecific memory T cells.