Influence of carvacrol on proliferation and survival of porcine lymphocytes and intestinal epithelial cells in vitro

Carvacrol, an essential oil compound of oregano and thyme, has potential applications as an alternative to antibiotic growth promoters in pig nutrition. Carvacrol is well known for its antibacterial effects, but it is unclear whether there are additional effects on the porcine immune system. In the present study, the influence of carvacrol on porcine blood lymphocytes was examined. The porcine enterocyte cell line IPEC-1 was examined for comparison. Carvacrol inhibited the proliferation of purified lymphocytes with an IC50 of 182 ± 67 μM in MTT assays. This was confirmed by CFSE assay. The presence of monocytes in carvacrol-treated lymphocyte preparations had a protective effect on the lymphocytes, significantly raising the IC50 to 516 ± 87 μM. FACS analysis of CFSE labelled lymphocyte subsets revealed that γδ T cells were less susceptible to carvacrol toxicity than CD4 and CD8 T cells. The reduced lymphocyte proliferation measured after carvacrol exposure was shown to be due to apoptotic cell death, as determined by annexin-V binding and caspase-3 activation. The observed effects were not specific for lymphocytes, since carvacrol similarly induced apoptosis and suppressed proliferation in the porcine enterocyte cell line IPEC-1.