The cellular immune response to respiratory syncytial virus (RSV) is felt to contribute to viral clearance and/or the inflammation accompanying pulmonary infections with this virus. Both tumor necrosis factor (TNF) and prostaglandin E2 (PGE2) are important regulatory mediators of the cellular immune response. We examined the production of these mediators from purified human alveolar and blood mononuclear phagocytes (MP) after RSV infection in vitro and compared production induced by virus with that induced by lipopolysaccharide (LPS). RSV infection of alveolar MP did not alter PGE2 production but increased expression of TNF alpha mRNA paralleled by increased secretion of immunoreactive and biologically active TNF. TNF production by alveolar MP was dependent on the infectious dose of virus and occurred early in the viral replication cycle. In contrast, RSV had minimal effects on blood MP production of TNF and PGE2. However, blood MP (and not alveolar MP) infected with RSV and costimulated with LPS demonstrated a 1.7-fold increase in PGE2 levels compared with LPS alone (P less than 0.001). Therefore, RSV has differential effects on human alveolar and blood MP production of these immunoregulatory molecules.