International Mammalian Genome Society

The 14th International Mouse Genome Conference (2000)

F8. Microarray Analysis of Heterogeneous Gene Expression during Mouse Macrophage Activation

Christine Wells, Timothy Ravasi, Darryl Houghton, Alistair Forrest, Sean Grimmond, Brandon Wainwright, Brendan McMorran and David Hume.

The activation of macrophages to produce a very wide range of inducible gene products is an essential event in innate and acquired immunity. Variation in this process between individuals underlies differential sensitivity to infectious disease. There is a wide spectrum of pathogen responsive phenotypes available across different inbred mouse strains. Three strains have been identified to date with mutations in the Toll-like receptor 4 gene, Tlr4, with a corresponding hyporesponsiveness to gram negative bacterial by products, specifically lipopolysaccaride (LPS). Tlr4 is located within the Brown deletion on chromosome 4, C3H/HeJ mice carry a dominant negative point mutation in the cytoplasmic domain and C57/Bl0ScNCr are null for the protein (1). Conversely, Balb/c and C57/Bl6 carry a mutation in the iron regulation gene Nramp1, increasing their susceptibility to Leishmania major.(2) Even within these well characterised models variability in macrophage response to specific pathogen by-products such as LPS, bacterial DNA and peptidoglycans points to the synergistic activation of a number of pathways (3, 4). Correspondingly, there is recent evidence that LPS induces at least 4 seperate signalling pathways, each independantly activating NF-kB(5).

We have begun an expression profiling program aimed at identifying the full spectrum of macrophage-expressed and inducible genes in the mouse genome. To this end we have focused on producing macrophage specific clone sets by combining existing cDNA resources (I.M.A.G.E., RIKEN) with our own subtracted libraries from LPS-stimulated macrophages. Initial screening results of a subtracted library confirm it to be highly informative for macrophage specific transcripts, and containing a number of novel ESTs.

cDNA microarrays produced from this clone set will provide us with the means to identify clusters of genes expressed in response to different macrophage-activating agonists across dosage and time courses. By studying the effects of genetic background on the pattern of macrophage gene activation we expect to identify novel genes contributing to the innate immune response.

1. Poltorak A etal (1998) Science 282(5396):2085-8

2.Videl SM, etal (1996) J. Immunology 157(8):3559-68

3. Vogel S, etal (1999) J. Immunology 162:5666-5670

4. Watson J, Riblet R and Taylor BA. (1977) J. Immunology 118(6) 2088-93.

5. Cario E, etal, (2000)J. Immunology 164:966-972.

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