CXCL2 and infection: In the case of environmental strains E5-Mex1, a significantly higher level of the pro-inflammatory cytokine IL-1β was seen in co-infected mice compared to mice infected with single species alone [P = 0.0586 (mixed versus E5) and P = 0.0134 (mixed versus Mex1)] while no differences in the level of CXCL1/KC and CXCL2/MIP-2 between co-infection and single infections were observed (Table 2).