Background: As common contaminants of agricultural commodities, aflatoxins (AFs) are highly hazardous carcinogenic mycotoxins originating from very common fungi present in the environment. Their effect on bovine key immunesurveillance molecules is unclear. Objective: To determine the in vitro effects of naturally occurring level of AFs on toll-like receptor-4 (TLR4) and viability in bovine peripheral blood mononuclear cells (PBMCs) as a model system for immunotoxicity. Methods: Ten healthy dairy cows were selected as a source of PBMCs. The mRNA expression of TLR4 was quantitatively evaluated in PBMCs treated with a mix of 1.0, 0.5, 0.25 and 0.25 ng/ml of AFB1, AFB2, AFG1 and AFG2, respectively, and 10 ng/ml of the well-known TLR4 agonist lipopolysaccharide (LPS) for 0.5, 2, 5 and 18 hours. We also analyzed the viability of PBMCs exposed to AFs by means of the trypan blue exclusion method and the tetrazolium bromide assay. Results: Compared with control PBMCs, transcription of TLR4 in AFs-treated PBMCs was significantly up-regulated at post-exposure hours (PEH) 2 and 5, but was unchanged at PEH 0.5 and 18. Unsurprisingly, much higher up-regulation of TLR4 transcript was observed in LPS-treated PBMCs at PEH 0.5, 2, 5 and 18. Conversely, the viability of post-AFs and/or LPS-exposed PBMCs revealed no significant changes. Conclusion: Naturally occurring levels of AFs result in increased expression of TLR4 mRNA in bovine PBMCs. Clinical importance: The increased expression of TLR4 mRNA in bovine PBMCs by AFs also emphasizes the need to reduce admissible levels of AFs in feed for preventive measures.

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