Evidence for CD4+ T cell responses common to Plasmodium falciparum and recall antigens.

In individual donors which have never been exposed to malaria parasites, the CD4+ T cell precursor frequencies for tetanus toxoid (TT) and Plasmodium falciparum responses are similar (range 1:850-1:4800). Limiting dilution cultures set up in response to P. falciparum trophozoites can be re-stimulated with the same stage of the parasite or TT and respond with similar frequencies. A substantial overlap in the responses to different agents was confirmed in suicide selection experiments where cells responding to malaria parasite, TT or influenza virus antigens were deleted using the cell cycle inhibitor cytosine arabinoside (Ara-C). The responses of the remaining cells to P. falciparum were almost completely abrogated and only weak responses were observed to different recall antigens (0.2-21% of untreated control). Little or no effect was observed on the responses to superantigen or mitogen. Furthermore, in contrast to superantigen, the observed responses to TT and Plasmodium were polyclonal, the blastoid cells generated reacting with a range of anti-TCR Vbeta antibodies with little preferential usage.