Interleukin 4 down‐regulates the expression of CD14 in normal human monocytes

Recombinant interleukin 4 (IL 4) down‐regulates the expression of CD 14 on normal human monocytes, as assessed by flow cytometry, binding assays with radiolabeled anti‐CD 14 monoclonal antibody (mAb), and immunoprecipitation of ¹²⁵I‐labeled monocytes with anti‐CD14 mAb. In parallel, CD23 expression on monocytes was strongly increased by IL4 stimulation, as assessed by both flow cytometry and immunoprecipitation. Down‐regulation of surface CD14 was first detectable after 24–36 h of incubation with rIL 4, and was almost complete after 4 days of culture. None of the other recombinant lymphokines tested (IL 1, IL 2, IL 3, IL 5, IL 6, interferon‐γ, tumor necrosis factor α and β, granulocytemacrophage colony‐stimulating factor) decreased CD14 expression. Metabolic labeling studies with [³⁵S]methionine showed that both the membrane‐associated and the soluble form of CD 14 are decreased by IL 4 stimulation. Northern blot analysis showed that incubation of monocytes with IL 4 induced a marked decrease in CD 14 mRNA. Nuclear run‐off assays revealed that the IL 4‐dependent down‐regulation of CD 14 resulted from decreased transcription. Thus, IL 4 exerts specific and opposite effects on the expression of monocytic antigens.