title: Suppression of Plasmodium falciparum by serum collected from a case of Plasmodium vivax infection.
abstract: BACKGROUND
  It has frequently been reported that Plasmodium vivax suppressed Plasmodium falciparum and ameliorated disease severity in patients infected with these two species simultaneously. The authors investigate the hypothesis that immunological responses stimulated by P. vivax may play a role in suppressing co-infecting P. falciparum.
  
  
  METHODS
  Sera, taken sequentially from one of the authors (YN) during experimental infection with P. vivax, were added to in vitro cultures of P. falciparum. Cross-reactive antibodies against P. falciparum antigens, and cytokines were measured in the sera.
  
  
  RESULTS
  Significant growth inhibitory effects upon P. falciparum cultures (maximally 68% inhibition as compared to pre-illness average) were observed in the sera collected during an acute episode. Such inhibitory effects showed a strong positive temporal correlation with cross-reactive antibodies, especially IgM against P. falciparum schizont extract and, to a lesser degree, IgM against Merozoite Surface Protein (MSP)-119. Interleukin (IL)-12 showed the highest temporal correlation with P. vivax parasitaemia and with body temperatures in the volunteer.
  
  
  CONCLUSIONS
  These results suggest the involvement by cross-reactive antibodies, especially IgM, in the interplay between plasmodial species. IL-12 may be one of direct mediators of fever induction by rupturing P. vivax schizonts, at least in some subjects. Future studies, preferably of epidemiological design, to reveal the association between cross-reactive IgM and cross-plasmodial interaction, are warranted.
authors.affiliation: Faculty of Tropical Medicine, Mahidol University,420/6 Rajvithi Road, Bangkok, 10400, Thailand. in_the_pacific214@yahoo.co.jp
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Nagao
authors.forename: Masako
authors.initials: M
authors.lastname: Kimura-Sato
authors.forename: Porntip
authors.initials: P
authors.lastname: Chavalitshewinkoon-Petmitr
authors.forename: Supatra
authors.initials: S
authors.lastname: Thongrungkiat
authors.forename: Polrat
authors.initials: P
authors.lastname: Wilairatana
authors.forename: Takafumi
authors.initials: T
authors.lastname: Ishida
authors.forename: Peerapan
authors.initials: P
authors.lastname: Tan-Ariya
authors.forename: J Brian
authors.initials: JB
authors.lastname: de Souza
authors.forename: Srivicha
authors.initials: S
authors.lastname: Krudsood
authors.forename: Sornchai
authors.initials: S
authors.lastname: Looareesuwan
mesh_terms: D000328:Adult; D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood; D000953:Antigens, Protozoan / Q000276:immunology; D003429:Cross Reactions; D006801:Humans; D007075:Immunoglobulin M / Q000097:blood; D018664:Interleukin-12 / Q000097:blood; D016780:Malaria, Vivax / Q000276:immunology*; D008297:Male; D010963:Plasmodium falciparum / Q000187:drug effects* / Q000254:growth & development / Q000276:immunology*; D010966:Plasmodium vivax / Q000276:immunology*; D044967:Serum / Q000276:immunology*
chemical_list: D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D007075:Immunoglobulin M; D018664:Interleukin-12