ABSTRACT
The development of eosinophilia in transgenic mice expressing interleukin-5 (IL-5) suggests that IL-5 expression is sufficient to induce the full pathway of eosinophil differentiation. Three important features of eosinophilia provide information about the mechanism of control of eosinophil production. First, eosinophilia is under the control of T lymphocytes. Second, increases in eosinophil numbers are frequently observed independently of increases in other blood leukocytes. Third, eosinophilia is observed in a restricted number of diseases, which indicates that the immune system is able to distinguish these particular types of antigenic challenge from the majority that do not induce eosinophils. The construct consisted of a truncated murine IL-5 cDNA flanked by rabbit beta-globin splice and polyadenylation sites, ligated to the mouse metallothionein promoter. The studies with human cells are consistent with the experiments with mouse cells, suggesting that IL-5 is a late-acting factor, and that eosinophil production requires other factors to cause the differentiation of eosinophil precursors from primitive stem cells.
