Epitope mapping of monoclonal antibody 1B9 against plasmodium falciparum-derived macrophage migration inhibitory factor.

A homologue of mammalian macrophage migration inhibitory factor (MIF) has been identified in Plasmodium falciparum (PfMIF). This parasite-derived cytokine and its antiserum were detected in the circulation of patients with malaria. Using a monoclonal antibody, designated mAb1B9, against PfMIF, we performed biopanning using two phage display peptide libraries to screen for the main sequence of the epitope recognized by the antibody. We then expressed a series of truncated peptides in order to identify the precise sequence of the epitope. The epitope recognized by mAb1B9 is 22 amino acids long and has the following sequence: (36)LGYIMSNYDYQKNLRFGGSNEA(57). Western analysis showed that the residues (36)LG(37) and (52)G differentiated PfMIF from the rodent malaria parasite-derived MIFs, and the residues (43)Y and (48)NL(49) differentiated PfMIF from P. vivax- and P. knowlesi-derived MIFs. The precise identification of this epitope, the first identified for PfMIF, will increase the specificity of the sandwich ELISA assays used to evaluate patients with malaria. These results indicate that mAb1B9 is useful for investigating the function of PfMIF in immune responses to malaria. Both the epitope and the monoclonal antibody against it will be valuable tools in epidemiological studies concerning this P. falciparum-derived cytokine.