Induction of CD 14 antigen on the surface of U937 cells by an interleukin‐6 autocrine mechanism after culture with formalin‐killed Gram‐negative bacteria

Abstract

In order to better understand the regulation of CD14 antigen on the surface of the monocyte-like cell line U937 in response to bacteria, the expression and regulation of CD14 antigen on these cells when cultured with formalin-killed bacteria were determined using the monoclonal antibody MY-4 and analyzed by means of the indirect immunofluorescence method. CD14 expression was induced on the U937 cells after about 48 hours of culture with all of the formalin-killed Gram-negative bacteria used in this study but with none of the Gram-positive bacteria. Maximum expression was obtained after culture with formalin-killed Salmonella enteritidis strain 116-54. Various cytokines such as interleukin-1 beta, interleukin-2, interleukin-6, interferon-gamma and tumor-necrosis factor-alpha were assayed in the culture supernatant of U937 cells cultured with or without formalin-killed Salmonella enteritidis 116-54 using an enzyme-immunoassay or radioimmunoassay system. The U937 cells were found to produce a large amount of interleukin-6 in response to formalin-killed Salmonella enteritidis 116-54. On the other hand, culture supernatant (referred to as conditioned medium) obtained from the U937 cells after 72 h of culture with formalin-killed Salmonella enteritidis 116-54 also induced strong expression of CD14 antigen 48 to 72 h later, and this was blocked by the addition of anti-human interleukin-6 antibody. These findings suggest that the expression of CD14 antigen on the surface of U937 cells cultured with formalin-killed Gram-negative bacteria is induced by interleukin-6 and can be explained on the basis of the autocrine mechanism of interleukin-6.