The role of regulatory CD4+CD25+ T cell subset in host homeostasis during protozoan infection: An overview

Human diseases caused by protozoan parasites are renowned for their high rates of morbidity and mortality worldwide. Some examples include African trypanosomiasis or sleeping sickness, American trypanosomiasis or Chagas disease, leishmaniases, malaria and babesiosis. These infections tend to follow a
chronic rather than an acute course with lifelong persistence of parasites. Regulatory T cells (Treg), in particular the CD4+CD25+ cell subset, appear to control the immune competence of host response triggered by the
presence of parasites, promoting homeostasis and protecting the host from collateral tissue damage whilst allowing parasite persistence. To date, there is still
considerable controversy on the characteristics and function of these cells when induced during diferente protozoan infections, evidencing the need of further
research. Therefore, this review aims to provide a comprehensive overview about Treg cells development, phenotype determination and general functions. The
above pathologies were used as selected examples to discuss the role of Treg cells during protozoan infections. Understanding of the mechanisms that contribute towards homeostasis and the survival of the host, and
simultaneously allow the persistence of the pathogen, may yield important insights for new strategies of prophylaxis and therapy .