Lymphotoxin: cloning, regulation and mechanism of killing

The gene for murine lymphotoxin (MuLT) has been cloned from a cDNA library prepared using poly(A)+ RNA from an activated murine IL-2-maintained cloned T cell line (21C11). This was accomplished with a MuLT BamHI fragment isolated from a murine genomic library by hybridization to a human LT cDNA probe. Northern blot analysis with RNA from 21C11, an L3T4+ (CD4+-equivalent) ovalbumin-specific class II-restricted T cell line, revealed a 15S band that hybridized to this MuLT fragment. A cDNA library prepared with poly(A)+ RNA from 21C11 cells contained 36 colonies that hybridized with the MuLT BamHI fragment. A full-length cDNA has been isolated, sequenced, expressed in COS-1 cells and used to map MuLT to mouse chromosome 17. The sequence and structure of the MuLT gene has been determined. MuLT cDNA has been used to analyse mRNA expression in several L3T4+ and Lyt-2+ (CD8+-equivalent) T cell clones activated with antigen, mitogen, or antibody to the T cell receptor. LT is expressed by both class I- and class II-restricted T cells. The mechanism of killing by both LT and the functionally related molecule TNF-alpha includes the induction of DNA fragmentation in the target cell.