CD40 and infection: Tests were performed to investigate whether there was any correlation between infection of PK-15 cells with CSFV and changes in the mRNA expression of host immune genes associated with the MHC antigen presentation pathway, such as MHC class I swine leukocyte antigen 2 (SLA-2), MHC class II swine leukocyte antigen DR (SLA-DR) and MHC class II-associated invariant chain (Ii), co-stimulation molecules (CD40, CD80, CD86), or host anti-viral Type I IFNs (IFN-α, IFN-β).