Dengue viruses were isolated by a plaque technique in LLC-MK2 cells from washed peripheral blood leukocytes of patients with hemorrhagic fever. In comparison with plasma, the use of peripheral blood leukocytes permitted greater than three times the recovery rate of viruses, allowed for the isolation of strains of virus from patients with high serum levels of antibody to dengue virus, and extended the period of detectable viremia. The use of peripheral blood leukocytes was especially useful for isolation of viruses from patients with hemorrhagic fever, in whom antibody titers were generally quite high during the acute phase of the disease. This method is recommended for use by laboratories with access to the appropriate acute-phase specimens. Of the peripheral blood leukocytes, adherent monocytes appeared to be the cells most likely affected; however, involvement of atypical lymphocytes, which are commonly found in patients with hemorrhagic fever, or polymorphonuclear leukocytes could not be excluded by this study. Only a small number of infected centers could be identified by infectious-center assays, but the marked augmentation of recovery of virus with the use of peripheral blood leukocytes indicated the presence in patients of a subpopulation of cells that permit dengue virus infection.

Peripheral leukocytes from 16 Thai children with dengue hemorrhagic fever were examined to determine the leukocyte composition on the day of presentation and on convalescent days 15 and 30. Mononuclear cells were isolated each time, and the concentrations of T, B, Fc receptor-bearing, and "null" cells were determined. On the day of hospitalization, in comparison to convalescent values, there was a significant increase in total lymphocytes, primarily due to concentrations of atypical lymphocytes. There was a significant loss of T cells with an increase in non-T, non-B, non-Fc receptor-bearing null cells. There were no changes in the concentrations of monocytes, B cells, or Fc receptor-bearing cells when acute and convalescent values were compared. During the convalescent period, a progressive increase in eosinophils was noted. Also, on day 15 but not on day 30 of the convalescent period, an increase was observed in the total leukocyte number due to an increase in granulocytes. There results indicate that in Thai children with dengue hemorrhagic fever, there are major shifts within several component cell subpopulations of the immune system.