Poster Presentation First Malaria World Congress 2018

Defining naturally acquired antibody kinetics and longevity to Plasmodium vivax antigens in western Thailand (#331)

Zoe Shih-Jung Liu 1 , Rhea Longley 1 2 , Eizo Takashima 3 , Matthias Harbers 4 , Takafumi Tsuboi 3 , Michael White 1 5 , Jetsumon Prachumsri 6 , Ivo Mueller 1 2 5
  1. Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
  2. Department of Medical Biology, University of Melbourne, Parkville, Victoria, Australia
  3. Proteo-Science Center, Ehime University, Matsuyama, Japan
  4. CellFree Sciences Co., Ltd., Yokohama, Japan
  5. Department of Parasites & Insect Vectors, Institut Pasteur, Paris, France
  6. Mahidol Vivax Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand

Plasmodium vivax is the dominant Plasmodium spp. in low-transmission regions outside of Africa. Such regions often feature asymptomatic patients with sub-microscopic parasitaemia and relapses. Naturally acquired antibody responses are induced after Plasmodium infection, providing partial protection against high parasitaemia and clinical episodes. However, previous work has failed to address such antibody responses to P. vivax particularly in low-transmission regions. We have recently conducted a study in western Thailand to monitor antibody kinetics for 9 months following symptomatic P. vivax infections, in the absence of recurrent infections during this time frame. Using AlphaScreen assay, we assessed IgG levels to 300 crude P. vivax proteins at 4 time points, and identified several P. vivax antigens that induce antibody responses with varying decay profiles. We have validated these results using Luminex, with purified proteins, to measure antibody levels at an increased number of time points to a sub-set of 40 antigens, to obtain antibody decay profiles of greater resolution. We found that the decay profiles captured using the two approaches are correlated, with antigens with short-lived antibody kinetic profiles better correlated than those inducing long-lived responses. For most antigens, an increase in antibody level was observed within the first week post symptomatic infection, followed by an exponential decay of different rates. We also observed a short-lived IgM response with a similar kinetic pattern which could last longer than 10 weeks above baseline for some antigens. Detailed analyses on IgG subclasses will be presented. Mathematical modelling of antibody responses allows further characterisation of the decay profiles, and investigation on the cause of variation in antibody kinetic profiles. Upon completion of this work, we will have gained invaluable insights into the development of naturally acquired immunity to P. vivax and the potential use of serology as a new surveillance tool for eliminating malaria.