SIRPA and infection: Interestingly, stimulation of pDC by co-culture with CSFV-infected or VRPΔErns -infected SK-6 cells induced up to 100-fold more IFN-α compared with direct infection of the pDC, with an optimum at 40'000 to 80'000 infected SK-6 cells per 2×105 CD172a+ enriched pDC (Figure 1A and B).