However, a previous study comparing the effect of H37Ra with H37Rv infection on chemokine and cytokine expression in mouse peritoneal macrophages, H37Ra was found to preferentially induce higher levels of mRNAs of IFN-inducible protein (IP-10), lymphotactin, macrophage inflammatory protein-3 (MIP-3), and fractalkine, but there were no significant differences in genes encoding pro-inflammatory cytokines (TNF-α, IL-1β, IL-12 and IL-6) (Freeman et al., 2006). Here, IL1B is linked to infection.