CCL2 and infection: However, pre-treatment with c-di-GMP significantly enhanced the production of MCP-1 prior to and at 24 hr post infection (P<0.004; Fig. 3) as well as the expression of MIP-2, mRNA levels (>3 fold increase; Fig. 4) at days 2 and 4 post challenge (P<0.005 and P<0.05 respectively).