T-cell tolerance as a potential effect of congenital leishmaniasis on offspring immunity.

Congenital transmission of leishmaniasis is recognized in cases detected by passive surveillance. Most cases are from low-resource countries, limiting the study of several important aspects of this route of infection, including the offspring's immune response. Studies on natural and experimentally infected animals suggest that parasites might be transmitted to the embryo or foetus at any time during pregnancy. As immune system undergoes sequential stages of development, an infection before the time of self-recognition could lead to central tolerance, making an individual specifically tolerant and susceptible to infection. In the alternative scenario, infection after self-recognition would allow the proper development of T-lymphocyte clones in response to Leishmania antigens, providing resistance to the disease. Newborns undergo a transient period of low expression of several immune surface molecules and a naïve adaptive immune response with no memory, which together might contribute to slow elimination of the parasite over several months. This insight is a proposed independent mechanism of the previously proven T-cell exhaustion and must be investigated. Analyses of infected placenta, cord blood and infant immunity are required for a better understanding of immunity in congenital leishmaniasis infection.