Immunogenicity of four Plasmodium falciparum preerythrocytic antigens in Aotus lemurinus monkeys

Abstract

Aotus lemurinus monkeys were immunized with pools of either lipid-tailed peptides injected in PBS or peptides in Montanide ISA-51, all derived from four Plasmodium falciparum pre-erythrocytic antigens, namely, LSA1, LSA3, SALSA, and STARP. These formulations were well tolerated. Their immunogenicity was demonstrated by the induction of both B- and T-cell responses to most of the peptides studied (of the 12, 10 induced antibody production, 9 induced T-cell proliferative responses, and all 12 induced gamma interferon secretion). Immune responses proved to be long lasting, since some were still detectable 210 days after immunization. Of particular importance is the fact that B- and T-cell responses elicited in this way by synthetic peptides were specific for native parasite proteins on P. falciparum sporozoites and liver stage parasites.

FIG. 1

T-cell proliferative responses and IFN-γ secretion. The stimulation index was calculated as the mean number of counts per minute of triplicate test cultures divided by the mean number of counts per minute of triplicate control cultures (nonstimulated cells) and was considered positive when >2. IFN-γ concentrations were calculated from a standard curve included in each plate and made by using culture medium containing known amounts of a standard IFN-γ (NIH-IFN-γ Gp23-901-530). Negative and positive controls (unstimulated cells and cells stimulated with phytohemagglutinin [PHA]) were included in each assay. Supernatants from human and Aotus phytohemagglutinin-stimulated blasts yielded similar values in the assay. Synthetic peptides and sonicated P. falciparum (P.f) sporozoite extracts (NF54 strain; a gift of W. Eling) were adjusted to a final protein concentration of 10 μg/ml. P. vivax (P.v) sporozoites (obtained from Anopheles albimanus mosquitoes fed on human blood samples) and noninfected A. albimanus mosquito salivary gland extracts were used as controls.