We compared the effects of live or inactivated bovine respiratory syncytial virus (BRSV) on cytokine production by bovine monocyte-derived dendritic cells (MoDC). We also investigated the response of resting memory CD4(+) T cells to MoDC exposed to both viral preparations. Although BRSV did not appear to replicate in MoDC or to affect expression of major histocompatibility complex (MHC) class I, MHC class II, or CD80/86, a higher percentage of cells exposed to live virus appeared to undergo apoptosis/necrosis. To investigate how the interaction of BRSV with MoDC affects the immune response, a multiplex, real-time, polymerase chain reaction was established to analyze transcription of bovine cytokines. Exposure of MoDC to live BRSV induced more interleukin (IL)-10 mRNA and markedly less IL-12p40 and IL-15 mRNA than did heat-inactivated virus. To determine whether these differences might influence the T cell response, CD4(+) memory T cells primed in vivo were restimulated in vitro by MoDC pulsed with heat-inactivated or live BRSV. Stimulation of CD4(+) T cells induced similar levels of IL-2-and IL-4-like activity and interferon-gamma. These observations suggest that while IL-10, produced by MoDC as a result of exposure to live BRSV, may affect IL-12 and IL-15 synthesis by MoDC, it does not appear to affect the cytokine response of BRSV-specific memory CD4(+) T cells. It is possible, however, that differences in the pattern of cytokines produced by MoDC exposed to live or inactivated virus may influence the development of the primary CD4(+) T cell response in vivo.