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.