Polyclonal expansion of peripheral γδ T cells in human plasmodium falciparum malaria

Abstract

Plasmodium falciparum malaria in humans is associated with an increase in the percentage and absolute number of γδ T cells in the peripheral blood. This increase begins during the acute infection phase and persists for at least 4 weeks during convalescence. In the present study, 25 to 30% of the γδ T cells expressed HLA-DR antigens in vivo and in some patients they proliferated in response to further stimulation by purified human interleukin 2 in vitro. However, there was no in vitro proliferative response to various malarial antigens, including a 75-kDa heat shock protein and a 72-kDa glucose-regulated protein of P. falciparum during the acute infection phase. Cytofluorographic studies showed that although an increase of Vδl- γδ T cells was largely responsible for the expansion of the total number of γδ T cells, there was also a proportional increase in Vδ1+ cells. These results were confirmed with anchored PCR and by DNA sequencing to characterize at the molecular level the set of T-cell receptor (TCR) δ mRNAs expressed in the peripheral blood of two patients with high levels of γδ T cells. In each case, most of the TCR δ mRNA transcripts corresponded to nonproductively rearranged δ genes (unrearranged Jδ or near Jδ spliced to Cδ). In those sequences which did represent productively rearranged genes, most of the transcripts originated from a Vδ2/Jδ1 joining, as in normal individuals. A minority of transcripts originated from a Vδ1/Jδ1 rearrangement, and one originated from a Vα4/Jδ1 rearrangement. Polyclonal activation of γδ T cells was inferred from the extensive junction diversity seen in the δ mRNAs analyzed. Expansion of a heterogeneous set of both Vδ1-- and Vδ1+- bearing T cells suggests that the elevated levels of γδ T cells seen during acute P. falciparum malaria arose from immune responses to multiple distinct parasite antigens or unidentified host factors.