title: MyD88 knockout mice develop initial enlarged periapical lesions with increased numbers of neutrophils.
abstract: OBJECTIVE
  To characterize the formation and progression of experimentally induced periapical lesions in teeth of MyD88 knockout (MyD88 KO) mice compared with wild-type (WT) mice.
  
  
  METHODS
  Periapical lesions were induced in the mandibular first molars of 30 WT and 30 MyD88 KO mice. After 7, 21 and 42 days, the animals were euthanized and the mandibles were subjected to histotechnical processing. Histological sections were stained with haematoxylin and eosin (HE), TRAP histoenzymology, Brown and Brenn staining and immunohistochemistry (RANK, RANKL, OPG). Data were subjected to statistical analysis by the nonparametric Mann-Whitney and Kruskal-Wallis tests and the Dunn post-test, using the SPSS software, version 17.0 (α = 0.05).
  
  
  RESULTS
  Regarding the periapical lesion size, the MyD88 KO group had significantly higher values than the WT group in the periods of 7 (P = 0.001) and 21 days (P = 0.05). A larger number of neutrophils in the MyD88 KO group were observed (P = 0.01 at 7 days, P = 0.004 at 21 days and P < 0.001 at 42 days). Regarding the number of osteoclasts, no statistically significant difference was observed between the groups at any of the experimental periods (P = 0.884 at 7 days, P = 0.506 at 21 days and P = 0.211 at 42 days).
  
  
  CONCLUSIONS
  In the absence of MyD88, the animals had larger periapical lesions, with a severe inflammatory infiltrate and a significantly larger number of neutrophils.
authors.affiliation: Department of Pediatric Dentistry, School of Dentistry of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil.
authors.forename: R A
authors.initials: RA
authors.lastname: Bezerra da Silva
authors.forename: P
authors.initials: P
authors.lastname: Nelson-Filho
authors.forename: M P
authors.initials: MP
authors.lastname: Lucisano
authors.forename: A
authors.initials: A
authors.lastname: De Rossi
authors.forename: A M
authors.initials: AM
authors.lastname: de Queiroz
authors.forename: L A
authors.initials: LA
authors.lastname: Bezerra da Silva
mesh_terms: D000818:Animals; D003786:Dental Pulp Cavity / Q000473:pathology; D018655:Lymphocyte Count; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000502:physiology*; D009504:Neutrophils / Q000473:pathology*; D010485:Periapical Periodontitis / Q000503:physiopathology*
chemical_list: C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88
keywords: MyD88 molecule; Toll-like receptors; knockout mice; periapical lesion