Demonstration of IL-1α and IL-1β secretion by the monocytic leukemia cell line, THP-1

This study examined the secretion of IL-1α and IL-1ß by THP-1 leukemia cells following activation with mezerein and promotion of synthesis by interferon (IFN-γ). Interleukin-1 (IL-1) was not detected by co-mitogenic thymocyte assays of crude supernates. Isoelectrofocusing of concentrated medium showed that all biologically active IL-1 migrated at a pH of 6.8-7.2, indicating that the major secreted form was IL-1β. Double antibody ELISA confirmed the presence of IL-1β, but failed to detect IL-1α in isofocused fractions. Although it appeared that THP-1 cells do not secrete IL-1α; an inhibitor of thymocyte response to IL-1 was present in conditioned medium, migrated in an acidic pH range and masked the expression of biologically active rIL-1α and rIL-1ß. In contrast, IL-1α was detected using a cell blotting assay. This technique permitted visualization of subpicogram levels of IL-1 when secreted by cells attached to an immunoblotting paper. Cell blotting showed that a greater proportion of attached cells incubated for 24 h in medium containing mezerein and IFN-γ secreted IL-1 than cells in control medium. In conclusion, the amount of immunoreactive or biologically active IL-1α secreted by stimulated THP-1 cells appeared to be much lower than that reported for human peripheral blood monocytes.