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CD4(+)T cells do not mediate within-host competition between genetically diverse malaria parasites

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Author

  • Victoria C Barclay
  • Lars Råberg
  • Brian H K Chan
  • Sheila Brown
  • David Gray
  • Andrew F Read

Summary, in English

Ecological interactions between microparasite populations in the same host are an important source of selection on pathogen traits such as virulence and drug resistance. In the rodent malaria model Plasmodium chabaudi in laboratory mice, parasites that are more virulent can competitively suppress less virulent parasites in mixed infections. There is evidence that some of this suppression is due to immune-mediated apparent competition, where an immune response elicited by one parasite population suppress the population density of another. This raises the question whether enhanced immunity following vaccination would intensify competitive interactions, thus strengthening selection for virulence in Plasmodium populations. Using the P. chabaudi model, we studied mixed infections of virulent and avirulent genotypes in CD4(+)T cell-depleted mice. Enhanced efficacy of CD4(+)T cell-dependent responses is the aim of several candidate malaria vaccines. We hypothesized that if immune-mediated interactions were involved in competition, removal of the CD4(+)T cells would alleviate competitive suppression of the avirulent parasite. Instead, we found no alleviation of competition in the acute phase, and significant enhancement of competitive suppression after parasite densities had peaked. Thus, the host immune response may actually be alleviating other forms of competition, such as that over red blood cells. Our results suggest that the CD4(+)-dependent immune response, and mechanisms that act to enhance it such as vaccination, may not have the undesirable affect of exacerbating within-host competition and hence the strength of this source of selection for virulence.

Publishing year

2008

Language

English

Pages

1171-1179

Publication/Series

Royal Society of London. Proceedings B. Biological Sciences

Volume

275

Issue

1639

Document type

Journal article

Publisher

Royal Society Publishing

Topic

  • Biological Sciences

Keywords

  • competition
  • malaria
  • CD4(+)T cells

Status

Published

Research group

  • Molecular Ecology and Evolution Lab

ISBN/ISSN/Other

  • ISSN: 1471-2954