ELISA for the presence of secreted Gro-1 chemokine in supernatants of subconfluent and polarized Caco-2 monolayers. (a) Subconfluent monolayers infected with wild-type, actA, and prfA bacteria under conditions used for microarray analysis. (b) ELISA assay for Gro-1 production by polarized Caco-2 cells. Wild-type L. monocytogenes (WT) was used to infect either apically (A-inf) or basolaterally (BL-inf). Supernatants from both apical (A) and basolateral (BL) membranes were analyzed for secreted Gro-1.