Plasmodium Cysteine Repeat Modular Proteins 3 and 4 are essential for malaria parasite transmission from the mosquito to the host

Abstract

Background: ThePlasmodiumCysteine Repeat Modular Proteins (PCRMP) are a family of four conserved proteins of malaria parasites, that contain a number of motifs implicated in host-parasite interactions. Analysis of mutants of the rodent parasitePlasmodium bergheilacking expression of PCRMP1 or 2 showed that these proteins are essential for targeting ofP. bergheisporozoites to the mosquito salivary gland and, hence, for transmission from the mosquito to the mouse.Methods: In this work, the role of the remaining PCRMP family members, PCRMP3 and 4, has been investigated throughout thePlasmodiumlife cycle by generation and analysis ofP. bergheigene deletion mutants, Δpcrmp3 and Δpcrmp4. The role of PCRMP members during the transmission and hepatic stages of thePlasmodiumlifecycle has been evaluated by light- and electron microscopy and by analysis of liver stage development in HEPG2 cellsin vitroand by infecting mice with mutant sporozoites. In addition, mice were immunized with live Δpcrmp3 and Δpcrmp4 sporozoites to evaluate their immunization potential as a genetically-attenuated parasite-based vaccine.Results: Disruption ofpcrmp3andpcrmp4inP. bergheirevealed that they are also essential for transmission of the parasite through the mosquito vector, although acting in a distinct way topbcrmp1and2. Mutants lacking expression of PCRMP3 or PCRMP4 show normal blood stage development and oocyst formation in the mosquito and develop into morphologically normal sporozoites, but these have a defect in egress from oocysts and do not enter the salivary glands. Sporozoites extracted from oocysts perform gliding motility and invade and infect hepatocytes but do not undergo further development and proliferation. Furthermore, the study shows that immunization with Δcrmp3and Δcrmp4sporozoites does not confer protective immunity upon subsequent challenge.Conclusions: PCRMP3 and 4 play multiple roles during thePlasmodiumlife cycle; they are essential for the establishment of sporozoite infection in the mosquito salivary gland, and subsequently for development in hepatocytes. However, although Δpcrmp3and Δpcrmp4parasites are completely growth-impaired in the liver, immunization with live sporozoites does not induce the protective immune responses that have been shown for other genetically-attenuated parasites.