TLR4 and immune system toxicity: Finally, we used quantitative real-time polymerase chain reaction (qRT-PCR) to examine changes in the expression patterns of toll-like receptor 2 (TLR2), toll-like receptor 4 (TLR4), and their downstream target genes following BB-80 and OH-BB-80 exposure to determine whether their immunotoxicity is mediated through the TLR/NF-κB signaling pathway.