**5. MSP-1 and its role in immunity and infection**

Our laboratory has focused on the major merozoite surface protein -1 (MSP-1). This antigen was identified in immune complexes from merozoite lysates (gp195), which provided the rationale for developing vaccines against it (Lyon et al., 1997). MSP-1 is first produced as a 195kD precursor that undergoes two successive proteolytic cleavage events (Blackman et al., 1994). The second processing event occurs immediately before invasion, resulting in the cleavage of the p42 molecule into a p33 and a p19 fragment. The p19 fragment remains attached to the merozoite surface through a GPI anchor (Gerold et al., 1996) and is comprised of two epidermal growth factor (EGF)-like domains (Morgan et al., 1999), which may have a role in the invading complex. Serological studies have provided significant evidence suggesting that immune responses directed against the C-terminus of MSP-1 (MSP-1p19 and MSP-1p42) are associated with immunity in preclinical models (Long et al., 1994; Egan et al., 1999; Darko et al., 2005; Parkkinen et al., 2006). Moreover, protective immunity as defined by lower mortality and morbidity of individuals residing in endemic areas was also associated with MSP-1p19 (Egan et al., 1999; John et al., 2004).
