Nitric oxide production induced by herpes simplex virus type 1 does not alter the course of the infection in human monocytic cells.

Undifferentiated U937 cells were not susceptible to herpes simplex virus type 1 (HSV-1) infection, but after differentiation with phorbol 12-myristate 13-acetate an increase in the permissivity to the virus was observed accompanied by the production of significant levels of viral particles. High levels of nitric oxide (NO) were produced in differentiated U937 cells infected with HSV-1. This production was comparable to that observed after addition of the NO donor glycerine trinitrate. The levels of NO drastically decreased when the cells were incubated with L-monomethyl arginine (L-NMA), an inhibitor of NO synthase. Although similar levels of NO were sufficient to decrease susceptibility of U937 cells to other viruses, neither incubation with NO donors nor addition of L-NMA altered the permissiveness to HSV-1 infection. Thus, these results suggest that NO does not interfere with the replication of HSV-1 in U937 cells.