Case report

Suppression of Plasmodium falciparum by serum collected from a case of Plasmodium vivax infection

Yoshiro Nagao¹ , Masako Kimura-Sato² , Porntip Chavalitshewinkoon-Petmitr¹ , Supatra Thongrungkiat¹ , Polrat Wilairatana¹ , Takafumi Ishida² , Peerapan Tan-ariya³ , J Brian de Souza⁴ , Srivicha Krudsood¹ and Sornchai Looareesuwan^{1^}

¹  Faculty of Tropical Medicine, Mahidol University,420/6 Rajvithi Road, Bangkok, 10400, Thailand

²  Department of Biological Sciences, Graduate School of Science, the University of Tokyo, Hongo 3, Bunkyo, Tokyo, Japan

³  Department of Microbiology, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand

⁴  Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK

author email corresponding author email^Deceased

Malaria Journal 2008, 7:113doi:10.1186/1475-2875-7-113

Published:	26 June 2008

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.

Conclusion

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.