title: Identification and characterization of novel gut-associated lymphoid tissues in rat small intestine.
abstract: BACKGROUND
  The crypt lamina propria of the mouse small intestine has been shown to harbor multiple tiny clusters filled with c-kit- and interleukin 7 receptor (IL-7R)-positive lympho-hemopoietic cells (cryptopatches; CPs). However, it has remained an open question whether similar lymphoid tissue are present in the gastrointesitinal tract in other animals. In the present study, we investigated whether the small intestine of rats harbored lymphoid tissues similar to mouse CPs.
  
  
  METHODS
  Immunohistochemical and flow cytometric analyses were carried out using various antibodies, including those to c-kit and IL-7R molecules.
  
  
  RESULTS
  Lymphocyte-filled villi (LFVs), populated predominantly with c-kit- and IL-7 receptor (IL-7R)-positive cells and less with T cell receptor (TCR)-alphabeta T cells were found throughout the small intestine of young adult rats. Although LFVs were absent from fetal rat intestine, they were first detected at around 2 weeks after birth. Notably, in most LFVs that settled in the antimesenteric wall of the small intestine in young adult rats, immunoglobulin M-positive B cells were also detectable at the bottom of the LFVs. In aged rats, lymphocytes in some LFVs displayed a different phenotype, comprising a large B-cell area that included a germinal center. Thus, these clusters represent the first description of isolated lymphoid follicles (ILFs) in the rat small intestine.
  
  
  CONCLUSIONS
  The present study provides the first evidence for c-kit- and IL-7R-positive lymphocyte clusters in the rat small intestine. Our data also indicating that LFVs and ILFs may constitute novel organized gut-associated lymphoid tissues in lamina propria of the rat small intestine.
authors.affiliation: Department of Microbiology and Immunology, School of Medicine, Keio University, Tokyo, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Hitotsumatsu
authors.forename: Hiromasa
authors.initials: H
authors.lastname: Hamada
authors.forename: Makoto
authors.initials: M
authors.lastname: Naganuma
authors.forename: Nagamu
authors.initials: N
authors.lastname: Inoue
authors.forename: Hiromasa
authors.initials: H
authors.lastname: Ishii
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Hibi
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Ishikawa
mesh_terms: D000818:Animals; D007421:Intestine, Small / Q000033:anatomy & histology*; D008221:Lymphoid Tissue / Q000033:anatomy & histology*; D051381:Rats; D017208:Rats, Wistar