Secondly, all Gram-positive bacteria, but none of the virus, induced IL-12p40 responses,
but the IL-12p40 responses did not affect Th1 cytokine production (IFN-γ). Instead, Th1 responses were correlated with the capacity to induce IFN-α secretion, which in cord cells were induced by S. aureus and influenza virus alone. These data imply that enveloped virus can deviate Th2 responses in human cord T cells. Allergic diseases among children and youth are one of the most common PF-02341066 cost chronic diseases in the Western world and the prevalence has increased drastically during the last 40 years . The hygiene hypothesis states that a reduced exposure to microbes increases the risk of developing allergies. This hypothesis was originally based on observations showing that children with many siblings, children
attending early day care or children growing up in poverty are less prone to develop allergies . It is, however, not yet clear which microbes that can and cannot affect allergy development. Epidemiological studies show that certain viral and bacterial infections correlate with a reduced incidence of allergic manifestations. HDAC inhibitor We have recently shown that infection with human herpes virus type 6 (HHV-6) is associated with reduced allergic sensitization in 18-month-old children . We have confirmed this in an experimental animal model of allergic asthma, where mice that are exposed to HHV-6 are protected against allergic inflammation. Mice exposed to HHV-6 have significantly lower levels of allergen-specific IgE, eosinophils and Th2 cytokines as compared to allergic control mice . In addition, previous infection with EBV [5, 6] and Hepatitis A virus [7, 8] has been associated with a reduced incidence of allergic sensitization and allergic symptoms in human subjects. Infection with orofecal and foodborne
bacteria, including Toxoplasma gondii and Helicobacter pylori, or exposure to bacterial components, such as endotoxin, have also been demonstrated during to be inversely related to atopic allergy [8–11]. Furthermore, the composition of the intestinal commensal flora has been suggested to affect the risk of developing allergic disease, where early colonization with bifidobacteria and lactobacilli is associated with a lower prevalence of allergy in young children (0–2 years of age) [12–14]. The allergic response is driven by Th2 cells, and their secretion of IL-4, IL-5 and IL-13. The initiation of the T cell response and the subsequent maturation of the T cells, including their differentiation into Th1 or Th2 cells, are regulated by dendritic cells (DC) . These cells are generally divided into two major subsets; myeloid CD11c+CD123− DC (mDC) and plasmacytoid CD11c−CD123+ DC (pDC). MDC are the main source of IL-12, which is pivotal in the differentiation of naïve CD4+ T cells into the favoured Th1 phenotype [16–18].