RESUMO
OBJECTIVE: Varicella is a common childhood infection and has a number of complications in the unvaccinated population. Perforin, found in natural killer cells, is important for the killing of virally infected cells. For this reason, the aim of this study was to determine natural killer cell count and activity, perforin expression, and Fas and soluble Fas ligand (sFas-L) levels in immunocompetent children with varicella infection and define any possible relations between the levels and varicella complications. METHODS: Forty children were analyzed at diagnosis and on the 15th day of varicella infection. There was a significant difference in hemoglobin levels and leukocyte and platelet counts between days 0 and 15. RESULTS: Thirteen (32%) patients were found to be lymphopenic. Natural killer cell count and activity were significantly higher on day 15 when compared to values at diagnosis. The Fas-mediated apoptotic pathway was found to be active in acute varicella infection because Fas and sFas-L levels at diagnosis were higher than values on day 15. CONCLUSION: These findings suggest that the Fas and Fas-L apoptotic pathway is active during the acute phase of the viral infection and that it becomes inactive by day 15, paralleling the hematologic recovery.