The present study assessed the immunomodulatory effects on macrophages of the following Penicillium mycotoxins (PMs), including citrinin (CIT), ochratoxin A (OTA), patulin (PAT), mycophilic acid (MPA) and penicillic acid (PA), by using a bovine macrophage cell line (BoMacs). Initially, concentration-response curves for each of these PMs were established based on cell proliferation and viability. The potency of these PMs based on their IC50s (concentration that inhibits 50% cell proliferation) from highest to lowest was: 0.56 µM (PAT) > 12.88 µM (OTA) > 29.85 µM (PA) > 91.20 µM (CIT) > not determined (MPA). LC50s (concentrations that kill 50% of cells) for PAT and PA were determined to be 4.46 μM and 175.79 μM, respectively. In addition to this, binary mixtures of some PMs at their respective IC25 and lower were shown to have significant interactions on cell proliferation. CIT+OTA had significant synergism, while PAT+MPA, CIT+MPA, CIT+PA and MPA+PA exhibited significant antagonism. PAT+PA showed significant antagonism at their respective IC25s, but were antagonistic at lower concentrations. The PMs at their sub-lethal levels of IC25s also differentially altered the gene expression of the following cytokines, including IL-1α, IL-6, IL-10, IL-12, IL-23 and TGF-β. Reactive oxygen species (ROS) production and phagocytosis of Mycobacterium avium subspecies paratuberculosis (MAP) was affected at higher sub-lethal concentrations. OTA in combination with CIT or PA synergistically suppressed the gene expression of the following epigenetic enzymes: DNA methyltransferases (DNMT-3s), histone demethylase (JMJD-3) and histone deacetylase (HDAC-3). When the efficacy of a mycotoxin-binding Mycosorb A+ (MA+), a mycotoxin binder, was assessed based on BoMac proliferation, 0.2% MA+ showed the highest efficacy in preventing OTA toxicity at pH 3.0, while its beneficial effect in preventing CIT toxicity was also observed with a longer incubation time than 6 hours and higher inclusion level of MA+ than 0.5%. The results from this thesis indicate that the PMs at their sub-lethal concentrations could potentially modulate the macrophage functions. These adverse effects also appear to be enhanced by PM interactions. This study also showed beneficial effect of MA+ in preventing the toxicity of PMs.