SummaryThe possible role of human neutrophils (PMN) as direct effector cells against free live virus particles was testedin vitro.Oxygen consumption, production of chemiluminescence and “virus killing” by PMNs was examined during and after incubation of cells and live or dead vaccinia virus with and without specific antibody. Oxygen consumption and chemiluminescence production occurred with unopsonized live but not with inactivated virus and was greatly enhanced with opsonization. Virus titers were determined in PMN-free supernatant and freeze-thawed cell pellet fractions after 15 min incubation. Reduction in titer from virus control was seen in supernatant fractions with and without opsonins, but in the cell fraction only with opsonins; the degree of reduction with opsonins was directly related to the opsonin source. PMNs from a patient with chronic granulomatous disease did not inhibit virus replication. These data suggest an active role for human PMNs in the genesis of and defense against virus infections and indicate areas for further investigation.SpeculationHuman neutrophils may play a role in the pathogenesis of and control of virus infections.