Thymol and carvacrol, two main components of thyme, have several valuable effects on the immune system. This study aims to evaluate the effects of these components on T-helper (TH) cell responses and their subsets in mice immunized with ovalbumin. The effects of these components on: a specific in vivo immune response were evaluated by assessing changes in delayed-type hypersensitivity (DTH); ex vivo splenocyte proliferative responses were evaluated using a BrdU assay gene expression of cytokines and key transcription factors involved in T-cells subset differentiation among the mouse splenocytes were assessed using real-time polymerase chain reaction (PCR); and splenocyte cytokine formation (ex vivo) and levels of the cytokines in mouse sera were measured by ELISA. Mice treated with thymol or carvacrol had reduced DTH responses (26% and 50%, respectively) compared with control mice. Thymol and carvacrol each diminished splenocyte proliferation to nearly 65-72% of control levels (p < 0.01). These agents also led to decreased TH1 [interleukin (IL)-2, interferon (IFN)-γ)], TH2 (IL-4) and TH17 (IL-17A) levels in the splenocyte cultures and in the sera of mice but increased levels of IL-10 and transforming growth factor (TGF)-β. Treated immunized mice showed significantly reduced T-box 21 (T-bet) expression from 3.8 [± 0.3]-fold in untreated ovalbumin-immunized mice to 0.9 [± 0.4]-(thymol) and 0.8 [± 0.2]-fold (carvacrol) (p < 0.01). GATA binding protein 3 (GATA-3) expression declined from 3.4 [± 0.4]- to 0.5 [± 0.3]-fold (thymol) and 0.6 [± 0.4]-fold (carvacrol), whereas RORγc decreased from 13.4 [± 1.6]- to 1.5 [± 0.6]-fold (thymol) and 0.8 [± 0.4]-fold (carvacrol) (p < 0.001). As carvacrol and thymol each suppressed the antigen-specific immune response by reducing TH cell-related cytokines\specific transcription factors, this indicated their potential to modulate destructive immune responses attributed to T-cells over-activation.
Keywords: Carvacrol; T-helper cells; immunization; immunomodulation; ovalbumin; thymol.