Lymphocyte subsets in healthy Malawians: Implications for immunologic assessment of HIV infection in Africa

Background: CD4(+)T lymphocyte measurements are the most important indicator of mortality in HIV-infected individuals in resource-limited settings. There is currently a lack of comprehensive immunophenotyping data from African populations to guide the immunologic assessment of HIV infection. Objective: To quantify variation in absolute and relative lymphocyte subsets with age in healthy Malawians. Methods: Lymphocyte subsets in peripheral blood of 539 healthy HIV-uninfected Malawians stratified by age were enumerated by How cytometry. Results: B and T-lymphocyte and T-lymphocyte subset absolute concentrations peaked in early childhood then decreased to adult levels, whereas lymphocyte subset proportions demonstrated much less variation with age. Adult lymphocyte subsets were similar to those in developed countries. In contrast, high B-lymphocyte and CD8(+)T-lymphocyte levels among children under 2 years, relative to those in developed countries, resulted in low CD4(+)T-lymphocyte percentages that varied little between 0 and 5 years (35% to 39%). The CD4(+)T-lymphocyte percentages in 35% of healthy children under 1 year and 18% of children age I to 3 years were below the World Health Organization threshold defining immunodeficiency in HIV-infected children in resource-limited settings. Thirteen percent of healthy children under 18 months old had a CD4:CD8T-lymphocyte ratio