Co-infection of monocytes with PRRSV-2 strain IAF-Klop and S. suis led to synergistic effects on the expressions of IL-6, CCL5, and TNF-α, and additive effects on productions of CCL4, CCL14, CCL20, IL-15, and PTGS2 (COX-2) [43]. Here, IL15 is linked to coinfection.