Toxoplasma gondii infection, atopy and autoimmune disease

While for many allergens a dose-response relationship has clearly been established the association between early childhood exposure to cat allergens and risk of sensitisation is still controversial and even inverse relations have been described. At the same time, a negative association between Toxoplasma gondii (T. gondii) infection and atopic diseases has been found in epidemiologic studies. As cats are the major source of T. gondii oocysts, we hypothesize that cat allergen exposure might be a confounder in the association between T. gondii infection and allergic diseases. Furthermore, it is well known that atopic diseases are T helper cell 2 (Th2) driven while autoimmune diseases are dominated by a Th1 response. A counterbalance between Th1 and Th2 cells has been postulated. However, it has been shown recently that subjects with autoimmune disease are more likely to suffer from atopic diseases. Therefore, similar cytokine profiles might underlie these disorders. If this holds true it can be hypothesised that T. gondii infection is associated with a lower prevalence of autoimmune disease.