title: Interleukin 5 plays an essential role in elicitation of contact sensitivity through dual effects on eosinophils and B-1 cells.
abstract: BACKGROUND
  Elicitation of contact sensitivity (CS) depends on B-1-cell-derived antigen-specific immunoglobulin M (IgM) antibodies that recruit CS effector T cells into the local tissue, which is followed by infiltration of antigen-nonspecific mononuclear cells and polymorphonuclear cells, such as neutrophils and eosinophils. In this study, we investigated the role of interleukin (IL)-5, which has broad effects on both eosinophils and B-1 cells, in elicitation of CS.
  
  
  METHODS
  IL-5 receptor alpha-chain-deficient (IL-5Ralpha-/-) mice and IL-5Ralpha+/+ mice were contact sensitized with oxazolone hapten. Four days later, mice were challenged with the same hapten, and ear swelling responses were measured at 24 h after challenge. Eosinophil infiltration into the local tissue was determined by examination of skin histology and eosinophil peroxidase activity. To investigate the role of IL-5 in B-1 cell activation, the number of oxazolone-specific IgM-producing cells in the spleen was determined by enzyme-linked immunospot assay.
  
  
  RESULTS
  Ear swelling responses in IL-5Ralpha-/- mice were about half of those in IL-5Ralpha+/+ mice, and nearly no eosinophil infiltration was observed in IL-5Ralpha-/- mouse skin. Eosinophil peroxidase activity in the sensitized and challenged IL-5Ralpha-/- mice was about 11 times less than that in immunized IL-5Ralpha+/+ mice. Contact sensitization significantly increased in numbers of oxazolne-specific IgM-producing cells in IL-5Ralpha+/+ mouse spleen, but not in IL-5Ralpha-/- mouse spleen.
  
  
  CONCLUSIONS
  We conclude that IL-5-dependent activation of eosinophils and B-1 cells is necessary for induction and elicitation of CS. These findings provide a new insight into complicated mechanisms of CS elicitation and suggest a novel role of IL-5 in the regulation of immune responses.
authors.affiliation: Division of Immunology, Department of Immunology and Microbiology, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
authors.forename: Atsuko
authors.initials: A
authors.lastname: Itakura
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kikuchi
authors.forename: Taku
authors.initials: T
authors.lastname: Kouro
authors.forename: Masashi
authors.initials: M
authors.lastname: Ikutani
authors.forename: Satoshi
authors.initials: S
authors.lastname: Takaki
authors.forename: Philip W
authors.initials: PW
authors.lastname: Askenase
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Takatsu
mesh_terms: D000276:Adjuvants, Immunologic / Q000494:pharmacology; D019264:Adoptive Transfer; D000818:Animals; D016175:B-Lymphocyte Subsets / Q000276:immunology*; D003877:Dermatitis, Contact / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D047209:Eosinophil Peroxidase / Q000378:metabolism; D004804:Eosinophils / Q000276:immunology*; D005260:Female; D006241:Haptens / Q000276:immunology; D007075:Immunoglobulin M / Q000096:biosynthesis / Q000276:immunology; D015848:Interleukin-5 / Q000172:deficiency / Q000276:immunology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D010081:Oxazolone / Q000276:immunology; D013154:Spleen / Q000276:immunology
chemical_list: D000276:Adjuvants, Immunologic; D006241:Haptens; D007075:Immunoglobulin M; D015848:Interleukin-5; D010081:Oxazolone; D047209:Eosinophil Peroxidase