Interleukin 5 Plays An Essential Role In Elicitation Of Contact Sensitivity Through Dual Effects On Eosinophils And B-1 Cells

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-5R alpha-/-) mice and IL-5R alpha+/+ 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-5R alpha-/- mice were about half of those in IL-5R alpha+/+ mice, and nearly no eosinophil infiltration was observed in IL-5R alpha-/- mouse skin. Eosinophil peroxidase activity in the sensitized and challenged IL-5R alpha-/- mice was about 11 times less than that in immunized IL-5R alpha+/+ mice. Contact sensitization significantly increased in numbers of oxazolne-specific IgM-producing cells in IL-5R alpha+/+ mouse spleen, but not in IL-5R alpha-/- mouse spleen. Conclusion: 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. Copyright (c) 2006 S. Karger AG, Basel.