CCL2 and parasitic infectious disease: Interestingly, this difference in serum levels of proinflammatory cytokines was transient, such that when mice were sacrificed at day 21 post-infection (a time when the difference in parasitemia was no longer significant), this difference in serum levels of TNF, MCP-1 and IL-6 between recipient and PBS control groups was no longer apparent (data not shown).