title: The bystander effect in optically trapped red blood cells due to Plasmodium falciparum infection.
abstract: BACKGROUND
  In a previous study of the properties of red blood cells (RBC) trapped in an optical tweezers trap, an increase in the spectrum of Brownian fluctuations for RBCs from a Plasmodium falciparum culture (due to increased rigidity) compared with normal RBCs was measured. A bystander effect was observed, whereby RBCs actually hosting the parasite had an effect on the physical properties of remaining non-hosting RBCs.
  
  
  METHODS
  The distribution of corner frequency (fc) in the power spectrum of single RBCs held in an optical tweezers trap was studied. Two tests were done to confirm the bystander effect. In the first, RBCs from an infected culture were separated into hosting and non-hosting RBCs. In the second, all RBCs were removed from the infected culture, and normal RBCs were incubated in the spent medium. The trapping environment was the same for all measurements so only changes in the properties of RBCs were measured.
  
  
  RESULTS
  In the first experiment, a similar and statistically significant increase was measured both for hosting and non-hosting RBCs. In the second experiment, normal RBCs incubated in spent medium started to become rigid after a few hours and showed complete changes (comparable with RBCs from the infected culture) after 24 h.
  
  
  CONCLUSIONS
  These experiments provide direct evidence of medium-induced changes in the properties of RBCs in an infected culture, regardless of whether the RBCs actually host the parasite.
authors: Department of Physics, Indian Institute of Science, Bangalore 560012, India. apurbapaul@physics.iisc.ernet.in
authors: Apurba
authors: A
authors: Paul
authors: Rani
authors: R
authors: Pallavi
authors: Utpal S
authors: US
authors: Tatu
authors: Vasant
authors: V
authors: Natarajan
mesh_terms: D024201:Bystander Effect / Q000187:drug effects / Q000502:physiology*; D003470:Culture Media / Q000494:pharmacology; D004912:Erythrocytes / Q000187:drug effects / Q000469:parasitology* / Q000502:physiology; D006801:Humans; D016778:Malaria, Falciparum / Q000097:blood* / Q000469:parasitology; D052898:Optical Tweezers; D010963:Plasmodium falciparum / Q000472:pathogenicity; D013059:Spectrum Analysis, Raman
chemical_list: D003470:Culture Media