Showing papers by "Christine Ambrose published in 1997"

Characterization of lymphotoxin-alpha beta complexes on the surface of mouse lymphocytes.

Abstract: The lymphotoxin-alpha beta complex (LT alpha beta) is found on the surface of activated lymphocytes and binds to a specific receptor called the LT beta receptor (LT beta R). In the mouse, signaling through this pathway is important for lymph node development and splenic organization, yet the biochemical properties of murine LT alpha and LT beta are essentially unknown. Here we have used soluble receptor-Ig forms of LT beta R and TNF-R55 and mAbs specific for murine LT alpha, LT beta, and LT beta R to characterize the appearance of surface LT alpha beta complexes and LT beta R on several common murine cell lines. Cells that bound LT beta R also bound anti-LT alpha and anti-LT beta mAbs in a FACS analysis. The ability of these reagents to discriminate between surface TNF and LT was verified by analysis of surface TNF-positive, LPS-activated murine RAW 264.7 monocytic cells. Primary mouse leukocytes from spleen, thymus, lymph node, and peritoneum were activated in vitro, and CD4+ and CD8+ T cells as well as B cells expressed surface LT ligand but not the LT beta R. Conversely, elicited peritoneal monocytes/macrophages were surface LT negative yet LT beta R positive. This study shows that on mononuclear cells, surface LT complexes and receptor are expressed similarly in mice and man, and the tools described herein form the foundation for study of the functional roles of the LT system in the mouse.

Cytotoxic activities of recombinant soluble murine lymphotoxin-alpha and lymphotoxin-alpha beta complexes.

Abstract: Human lymphotoxin-alpha (LT alpha) is found in a secreted form and on the surface of lymphocytes as a complex with a second related protein called lymphotoxin-beta (LT beta). Both secreted human LT alpha and TNF have similar biological activities mediated via the TNF receptors, whereas the cell surface LT alpha beta complex binds to a separate receptor called the LT beta receptor (LT beta R). The murine LT alpha and LT beta (mLT alpha and mLT beta) proteins have never been characterized. When recombinant mLT alpha was produced by either of several methods, the protein had a very low specific activity relative to that of human LT alpha in the conventional WEHI 164 cytotoxicity bioassay. The weak activity observed was inhibited by a soluble murine TNF-R55 Ig fusion protein (mTNF-R55-Ig), but not by mLT beta R-Ig. Coexpression of both mLT alpha and a soluble version of mLT beta in insect cells led to an LT alpha beta form that was cytotoxic in the WEHI 164 assay via the LT beta R. To determine whether natural mLT alpha-like forms with cytotoxic activity comparable to that of secreted human LT alpha were secreted from primary spleen cells, splenic lymphocytes were activated in various ways, and their supernatants were analyzed for cytotoxic activity. Using specific Abs to distinguish between mTNF and mLT, a TNF component was readily detected; however, there was no evidence for a secreted mLT alpha cytotoxic activity using this assay. Combined, these observations suggest that secreted mLT alpha may not play a role in the mouse via interactions with TNF-R55, and the ramifications of this hypothesis are discussed.

Exon trapping and sequence-based methods of gene finding in transcript mapping of human 4p16.3.

Abstract: We have applied exon amplification, GRAIL2 exon prediction and EST database searching to a 2 Mb segment of chromosome 4p 16.3. Experimental and computational methods of identifying exons were comparable in efficiency and apparent false positive rate, but were complementary in gene identification, revealing distinct overlapping sets of expressed sequences. EST searching was most powerful when we considered only those ESTs that show evidence of splicing relative to the genomic sequence. The combination of the three gene finding methods produced a transcription map of 30 loci in this segment of 4p16.3 that includes known human genes, homologs of loci identified in rodents and several anonymous transcripts, including a putative novel DNA polymerase and a gene related toDrosophila ash1. While most of the genes in the region have been found, our data suggest that even with the entire DNA sequence available, complete saturation of the transcript map will require additional, focused experimental effort.