title: A microarray analysis of gnotobiotic mice indicating that microbial exposure during the neonatal period plays an essential role in immune system development.
abstract: BACKGROUND
  Epidemiological studies have suggested that the encounter with commensal microorganisms during the neonatal period is essential for normal development of the host immune system. Basic research involving gnotobiotic mice has demonstrated that colonization at the age of 5 weeks is too late to reconstitute normal immune function. In this study, we examined the transcriptome profiles of the large intestine (LI), small intestine (SI), liver (LIV), and spleen (SPL) of 3 bacterial colonization models-specific pathogen-free mice (SPF), ex-germ-free mice with bacterial reconstitution at the time of delivery (0WexGF), and ex-germ-free mice with bacterial reconstitution at 5 weeks of age (5WexGF)-and compared them with those of germ-free (GF) mice.
  
  
  RESULTS
  Hundreds of genes were affected in all tissues in each of the colonized models; however, a gene set enrichment analysis method, MetaGene Profiler (MGP), demonstrated that the specific changes of Gene Ontology (GO) categories occurred predominantly in 0WexGF LI, SPF SI, and 5WexGF SPL, respectively. MGP analysis on signal pathways revealed prominent changes in toll-like receptor (TLR)- and type 1 interferon (IFN)-signaling in LI of 0WexGF and SPF mice, but not 5WexGF mice, while 5WexGF mice showed specific changes in chemokine signaling. RT-PCR analysis of TLR-related genes showed that the expression of interferon regulatory factor 3 (Irf3), a crucial rate-limiting transcription factor in the induction of type 1 IFN, prominently decreased in 0WexGF and SPF mice but not in 5WexGF and GF mice.
  
  
  CONCLUSIONS
  The present study provides important new information regarding the molecular mechanisms of the so-called "hygiene hypothesis".
authors: Center for Kampo Medicine, Keio University School of Medicine, 35 Shinano-machi, Shinjuku-ku, Tokyo, 160-8582, Japan.
authors: Masahiro
authors: M
authors: Yamamoto
authors: Rui
authors: R
authors: Yamaguchi
authors: Kaori
authors: K
authors: Munakata
authors: Kiyoe
authors: K
authors: Takashima
authors: Mitsue
authors: M
authors: Nishiyama
authors: Kyoji
authors: K
authors: Hioki
authors: Yasuyuki
authors: Y
authors: Ohnishi
authors: Masao
authors: M
authors: Nagasaki
authors: Seiya
authors: S
authors: Imoto
authors: Satoru
authors: S
authors: Miyano
authors: Atsushi
authors: A
authors: Ishige
authors: Kenji
authors: K
authors: Watanabe
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001419:Bacteria / Q000378:metabolism*; D016000:Cluster Analysis; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D005856:Germ-Free Life / Q000235:genetics* / Q000276:immunology*; D007107:Immune System / Q000254:growth & development* / Q000382:microbiology*; D007421:Intestine, Small / Q000254:growth & development / Q000378:metabolism; D008099:Liver / Q000254:growth & development / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D005810:Multigene Family / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods*; D009928:Organ Specificity / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics; D013154:Spleen / Q000254:growth & development / Q000378:metabolism; D051193:Toll-Like Receptors / Q000235:genetics / Q000378:metabolism
chemical_list: D051193:Toll-Like Receptors