Increased Thymic Output during Acute Measles Virus Infection

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Abstract
Measles virus infects thymic epithelia, induces a transient lymphopenia, and impairs cell-mediated immunity, but thymic function during measles has not been well characterized. Thirty Zambian children hospitalized with measles were studied at entry, hospital discharge, and at 1-month follow-up and compared to 17 healthy children. During hospitalization, percentages of naïve (CD62L + , CD45RA + ) CD4 + and CD8 + T lymphocytes decreased ( P = 0.01 for both), and activated (HLA-DR + , CD25 + , or CD69 + ) CD4 + and CD8 + T lymphocytes increased ( P = 0.02 and 0.03, respectively). T-cell receptor rearrangement excision circles (TRECs) in measles patients were increased in CD8 + T cells at entry compared to levels at hospital discharge ( P = 0.02) and follow-up ( P = 0.04). In CD4 + T cells, the increase in TRECS occurred later but was more sustained. At discharge, TRECs in CD4 + T cells ( P = 0.05) and circulating levels of interleukin-7 ( P = 0.007) were increased compared to control values and remained elevated for 1 month, similar to observations in two measles virus-infected rhesus monkeys. These findings suggest that a decrease in thymic output is not the cause of the lymphopenia and depressed cellular immunity associated with measles.