Host Genetics and Responses - Project D1

Susceptibility to and manifestation of malaria: role of iron deficiency and polymorphisms of iron regulation

Host lab: Frank Mockenhaupt (Charité)

Partner labs at ANU: TBA

Background: Iron deficiency (ID) inhibits Plasmodium growth, increases parasite phagocytosis, and reduces malaria risk. Upregulation of the iron master-regulator hepcidin due to malaria or inflammation reduces hepatic parasite survival. Several host polymorphisms influence iron status whereas hepcidin is regulated by inflammation. We have previously shown that ID as well as a common ferroportin polymorphism associate with relative resistance to malaria.

Scope/central question: We hypothesize that common polymorphisms of iron and hepcidin regulation influence, directly or via ID, risk and manifestation of P. falciparum and P. vivax malaria. Moreover, we hypothesize that iron-deficient parasitized RBCs undergo enhanced phagocytosis and that this is paralleled by enhanced activation of innate immune responses.

Methods: Based on available samples and prospective field studies, we will type host polymorphisms involved in iron/hepcidin regulation, compare frequencies between patients and controls, and calculate associations with malaria risk and iron biomarkers. In vitro, red blood cells (RBCs) with and without ID, iron chelator treatment, and/or polymorphisms of interest (obtained from patients and volunteers) will be used to assess Plasmodium falciparum growth and phagocytosis (each, groups of 5-15). Parasite multiplication will be monitored by microscopy and flow cytometry. Phagocytosis activity will be assessed microscopically and by ELISA applying co-cultures of P. falciparum-infected RBCs (>90% parasitaemia, MACS separated) and monocytes from malaria naïve donors. Innate immune activation will be determined by cytokine concentrations in supernatants (ELISA). Surface variation of infected RBCs, e.g. in ID, will be identified by high resolution scanning microscopy, and analysis of surface membrane components and adhesion properties.

Outline of 3-year plan: year 1: genetic association studies, in vitro assays (Charité), possibly field study (Rwanda); year 2: membrane components and adhesion properties (ANU); year 3: continued in vitro assays, statistical analysis, write-up (Charité).

Keywords: Iron deficiency, hepcidin, polymorphism