Eosinophil recruitment into sites of delayed‐type hypersensitivity reactions in mice

The selective accumulation of eosinophils in tissue is a characteristic feature of allergic diseases where there is a predominance of lymphocytes expressing a Th2 phenotype. In an attempt to define factors determining specific eosinophil accumulation in vivo , we have used a radiolabeled technique to assess the occurrence and the mechanisms underlying 111 In‐eosinophil recruitment into Th1‐ and Th2‐predominant, delayed‐type hypersensitivity (DTH) reactions. Eosinophils were purified from the blood of IL‐5 transgenic mice, labeled with 111 In and injected into nontransgenic CBA/Ca mice. Th1‐ and Th2‐predominant, DTH reactions were induced in mice by immunization with methylated bovine serum albumin (MBSA) in Freund’s complete adjuvant or with Schistosoma mansoni eggs, respectively. In these animals, 111 In‐eosinophils were recruited in skin sites in an antigen‐, time‐, and concentration‐dependent manner. Depletion of CD4 + lymphocytes abrogated 111 In‐eosinophil recruitment in both reactions. Pretreatment of animals with anti‐IFN‐γ mAb abrogated 111 In‐eosinophil recruitment in MBSA‐immunized and ‐challenged animals, whereas anti‐IL‐4 inhibited 111 In‐eosinophil recruitment in both models. Local pretreatment with an anti‐eotaxin polyclonal antibody inhibited the MBSA and SEA reactions by 51% and 39%, respectively. These results demonstrate that, although eosinophilia is not a feature of Th1‐predominant, DTH reactions, these reactions produce the necessary chemoattractants and express the necessary cell adhesion molecules for eosinophil migration. The control of the circulating levels of eosinophils appears to be a most important strategy in determining tissue eosinophilia.