ILA, THE HUMAN 4-1BB HOMOLOG, IS INDUCIBLE IN LYMPHOID AND OTHER CELLLINEAGES

We recently identified a gene that is induced by lymphocyte activation (ILA). The sequence of the full-length 1.4-kb cDNA characterized ILA as a new member of the nerve growth factor/tumor necrosis factor (NGF/ TNF) receptor family and the human homologue of the murine T-cell-spec ific receptor 4-1BB. The present study demonstrates ILA mRNA isoforms at 4.4, 4.0, and 1.8 kb in poly-A(+) RNA from activated, but not from resting human peripheral blood T lymphocytes. A reverse transcriptase- polymerase chain reaction (RT-PCR) assay was used to study tissue dist ribution and regulation of ILA expression. The gene was induced in T l ymphocytes by phytohemagglutinin (PHA), phorbol myristate acetate (PMA ), and antibody to CD3, in B lymphocytes by PMA and antibodies to cell surface Ig, and in blood monocytes by interleukin-1 beta (IL-1 beta), lipopolysaccharide (LPS), and PMA. In T lymphocytes, ILA mRNA was det ectable 1.5 hours after stimulation, reached maximal levels at 8 hours , and declined to background levels by 48 hours. Induction of ILA mRNA required protein synthesis and was primarily due to increased transcr iption. Actinomycin D reduced ILA mRNA levels in activated lymphocytes 50% within 30 minutes, demonstrating a relatively short half-life of this mRNA, Analysis of nonlymphoid cells showed that ILA mRNA was not detectable in resting cells. However, in contrast to the lymphoid-spec ific expression of the murine 4-1BB gene, ILA was detected in nonlymph oid cells, including epithelial and hepatoma cells after stimulation w ith IL-1 beta. ILA was not detectable in several brain derived cell li nes. The ILA cDNA encodes a 30-kD protein as demonstrated by in vitro translation, and this protein is immunoprecipitated by antisera that w ere raised against ILA peptides or a glutathione-S-transferase fusion protein. Flow cytometry showed expression of ILA protein on a subset o f activated T or B lymphocytes. In conclusion, activation-dependent ex pression of ILA is found not only in T lymphocytes, but also in B lymp hocytes, monocytes, and diverse nonlymphoid cell types. (C) 1995 by Th e American Society of Hematology.