Noncleavable transmembrane mouse tumor necrosis factor-alpha (TNF alpha) mediates effects distinct from those of wild-type TNF alpha in vitro and in vivo

Tumor necrosis factor-alpha (TNF alpha) exists in two biologically active f orms, a 26-kDa transmembrane form and a proteolytically cleaved and secrete d form. We sequentially inactivated all three known cleavage sites of mouse TNF alpha by mutating the corresponding DNA sequences. A murine T cell hyb ridoma transfected with the nonsecretable mutant TNF alpha efficiently lyse d L929 target cells in a cell contact-dependent manner and induced expressi on of vascular cell adhesion molecule-1 on mouse endothelioma cells. A geno mic mouse TNF alpha clone encoding this mutant was subsequently introduced as a transgene into TNF alpha(-/-) lymphotoxin-alpha(-/-) mice. The 3' AU-r ich regulatory elements of the TNF locus were maintained in the transgene t o assure adequate gene regulation. Transmembrane TNF alpha transgenic mice were fully protected from endotoxic shock, and no TNF alpha bioactivity was detectable in the serum after stimulation with lipopolysaccharide. Activat ed CD4 T cells from these animals, however, lysed L929 cells in a cell cont act-dependent way. After administration of Lipopolysaccharide, transmembran e TNF alpha transgenic mice produced significantly higher levels of interle ukin-12 than wild-type mice or TNF-deficient mice. This indicates that tran smembrane TNF alpha may greatly affect the course of a cellular immune resp onses in vivo and exerts quantitatively and qualitatively distinct function s from secreted TNF alpha in vitro and in vivo.