IL1B and infection: THP-1 macrophages were exposed to equal amounts of viable Y. enterocolitica, ΔyopBY. enterocolitica, or heat-treated Y. enterocolitica (multiplicity of infection [MOI] of 50) for 2 h, followed by quantification of a PGE2 and IL-1β by enzyme-linked immunosorbent assay (ELISA).