Essentials for starting a pediatric clinical study (2): Role of environment and immunity in the development of childhood allergic and immunologic disorders

Abstract

Regulatory T- (T_REG) cells are considered to inhibit the development of both type 1 and type 2 helper T (T_H1 and _TH2) cells. However, the number of T_REG cells in patients with allergic diseases who have high levels of serum IgE and blood eosinophils is reduced as compared to individuals who have similarly high levels of IgE and eosinophils but are asymptomatic. Therefore, T_REG cells may suppress the onset of allergic disease by downregulating other types of immune cells besides T_H1 and T_H2 cells. The newly discovered interleukin (IL-)17-producing helper T- (T_H17) cells responsible for autoimmune inflammatory diseases may counteract with T_REG cells even in allergic diseases. T_H2 cells capable of producing of high levels of tumor necrosis factor (TNF)-a may also be involved in the inflammation in allergic diseases. In this review, the role of T_H1, T_H2, T_H17 and T_REG cells in allergic diseases is further discussed by using the balancing square model and the factors differentiating between patients with clinical manifestations of allergic symptomatic versus atopic individuals who are sensitized but asymptomatic.