FIGURE 2.

Porcine reproductive and respiratory syndrome virus-infected MØ are strong inducers of IFN-α production by pDC. (A) RVB-581-infected MARC-145 cells do not induce a stronger IFN-α secretion by pDC compared with the free viral particles effect on enriched pDC alone. MARC-145 cells were infected with RVB-581 for 90 min, washed and then co-cultured with enriched pDC. Stimulation of pDC by PRRSV virions (MOI 0.1 TCID₅₀/cell) was used as control. (B) PRRSV-infected MØ are more potent activators of pDC as compared to virions (“alone”). Infection of cells was performed as in (A) using four different strains. (C) Stimulation of pDC by infected MØ but not by virions requires live virus. pDC were stimulated either with virions (“alone,” live or inactivated [UV]) or with infected MØ (“MØ”) as described in (A). (D) pDC cultured in inserts of trans-well plates were either stimulated with virions (“alone”), by contact with infected MØ (“MØ”) or were physically separated from the infected MØ (“MØ tw”). CpG D32 was used as a control for strong pDC activation. All data are the result of experiments performed in triplicate with 20 h of stimulation, with error bars representing the standard deviation. The figures are representative of three (A,B) and two (C,D) different experiments.