Effect of Penicillium mycotoxins on bovine macrophage (BoMac) function
Penicillium mycotoxins (PM) are natural contaminants that are commonly found in improperly stored animal feeds. Although exposure to certain PMs has been reported to affect immune function, little data are available for ruminant species. Therefore, in this study bovine macrophages (BoMacs) were exposed to the following PM: citrinin (CIT), ochratoxin A (OTA), patulin (PAT), mycophenolic acid (MPA) and penicillic acid (PA), and macrophage function was assessed by measuring cytokine gene expression, the production of reactive oxygen species (ROS), and phagocytosis of Mycobacterium avium ssp. Paratuberculosis (MAP), which is the causative agent of Johne’s disease.
Real-time PCR analysis of pro-inflammatory cytokines interleukin (IL)-1α and IL-6, anti-inflammatory cytokines IL-10 and transforming growth factor-beta (TGF)-B, as well as neutrophil stimulating cytokines IL-12 and IL-23 was assessed following 6 and 24 hr of PM exposure at concentrations that inhibited BoMac proliferation by 25% (IC25). The mycotoxin treatments altered the gene expression of cytokines at 24 hr. Ochratoxin A induced IL-1α expression (P < 0.05), while IL-6 expression was suppressed (P < 0.01). Mycophenolic acid induced the IL-1α expression (P < 0.05) and reduced the expression of IL-12α (P < 0.01) and IL-10 (P < 0.01). Patulin suppressed the expression of IL-23 (P < 0.01), IL-10 (P < 0.05) and TGF-b (P < 0.05). Neither CIT, nor PA affected the expression of these genes. The mycotoxins also affected BoMac intracellular ROS production and phagocytosis at the higher concentrations. Pretreatment with CIT at 300.0 µM increased pathogen associated molecule (PAM)-3-induced ROS production, which appeared to contribute to cell death. In contrast, PAT and PA significantly decreased the ROS production at concentrations ranging from 1.3 µM to 10.0 µM and from 31.3 µM to 125.0 µM, respectively; these two PMs simultaneously increased BoMac viability at 10.0 µM and 125.0 µM, respectively, even though they caused the cell death at higher concentrations. Although OTA did not affect the ROS production, an increasing trend in the phagocytosis of MAP was observed from 3.1 to 12.5 µM. In contrast, a decreasing trend in phagocytosis was observed for PAT concentrations from 2.5 to 10.0 µM. These findings suggest that exposure to sublethal concentrations of PM can alter immune function, which could affect innate antimicrobial resistance and immunoregulation.
Keywords: Penicillium mycotoxins, bovine macrophages, and immunomodulation