BACKGROUND: Lymphocyte subsets in healthy children are currently characterized by age-related standards. Because antigenic stimuli play a role in maturation of the immune system after birth, there is a question of whether cellular immune development differs in infants whose living conditions entail extensive antigenic exposure and infants growing up in a more protected environment. METHODS: Peripheral blood lymphocyte subsets were studied in two populations of children of similar age and nutritional status; children belonging to a rural population residing in proximity with farm animals and children from an economically privileged urban population. In each population, children studied included a group with an acute diarrheal episode and a healthy control group. RESULTS: Among rural population children, 65% had experienced at least one episode of gastroenteritis within the previous 3-month-period, compared with less than 10% of urban population children. In the rural population group 15% had experienced two or more episodes of gastroenteritis. The proportion of helper T cells was similar in rural population and urban population children. Among helper T cells, the proportion of CD29+ "memory" cells of the total CD4+ helper T cells was more than two times higher than those in rural population children. The proportion of CD8 cells was higher in rural population children than in urban population children, and the proportion of natural killer cells, CD56+ and CD57+, was two to three times higher in rural population children. Within each population, peripheral blood lymphocyte subsets did not differ between the healthy control group and those with acute diarrhea. CONCLUSIONS: In young children exposure to environmental pathogens and specifically to gastrointestinal antigenic stimuli is a major factor affecting development of the cellular immune response. Young children who have experienced enhanced infectious exposure have a peripheral blood lymphocyte profile similar to that of adults.
BACKGROUND: Lymphocyte subsets in healthy children are currently characterized by age-related standards. Because antigenic stimuli play a role in maturation of the immune system after birth, there is a question of whether cellular immune development differs in infants whose living conditions entail extensive antigenic exposure and infants growing up in a more protected environment. METHODS: Peripheral blood lymphocyte subsets were studied in two populations of children of similar age and nutritional status; children belonging to a rural population residing in proximity with farm animals and children from an economically privileged urban population. In each population, children studied included a group with an acute diarrheal episode and a healthy control group. RESULTS: Among rural population children, 65% had experienced at least one episode of gastroenteritis within the previous 3-month-period, compared with less than 10% of urban population children. In the rural population group 15% had experienced two or more episodes of gastroenteritis. The proportion of helper T cells was similar in rural population and urban population children. Among helper T cells, the proportion of CD29+ "memory" cells of the total CD4+ helper T cells was more than two times higher than those in rural population children. The proportion of CD8 cells was higher in rural population children than in urban population children, and the proportion of natural killer cells, CD56+ and CD57+, was two to three times higher in rural population children. Within each population, peripheral blood lymphocyte subsets did not differ between the healthy control group and those with acute diarrhea. CONCLUSIONS: In young children exposure to environmental pathogens and specifically to gastrointestinal antigenic stimuli is a major factor affecting development of the cellular immune response. Young children who have experienced enhanced infectious exposure have a peripheral blood lymphocyte profile similar to that of adults.