CD4+ T Cell Responses to the Plasmodium falciparum Erythrocyte Membrane Protein 1 in Children with Mild Malaria

The immune response against the variant surface Ag Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is a key component of clinical immunity against malaria. We have investigated the development and maintenance of CD4(+) T cell responses to a small semiconserved area of the Duffy binding-like domain (DBL)alpha-domain of PfEMP1, the DBL alpha-tag. Young children were followed up longitudinally, and parasites and PBMCs were isolated from 35 patients presenting with an acute case of uncomplicated malaria. The DBL alpha-tag from the PfEMP1 dominantly expressed by the homologous parasite isolate was cloned and expressed as recombinant protein. The recombinant DBL alpha-tag was used to activate PBMCs collected from each acute episode and from an annual cross-sectional survey performed after the acute malaria episode. In this article, we report that CD4(+) T cell responses to the homologous DBL alpha-tag were induced in 75% of the children at the time of the acute episode and in 62% of the children at the following cross-sectional survey on average 235 d later. Furthermore, children who had induced DBL alpha-tag-specific CD4(+)IL-4(+) T cells at the acute episode remained episode free for longer than children who induced other types of CD4(+) T cell responses. These results suggest that a wide range of DBL alpha-tag-specific CD4(+) T cell responses were induced in children with mild malaria and, in the case of CD4(+)IL-4(+) T cell responses, were associated with protection from clinical episodes.