Figure 3.

Cytotoxic immune responses upon in vitro Plasmodium falciparum–infected red blood cell stimulation 1 day before challenge infection (C − 1). Each symbol represents a single protected (black symbols) or chemoprophylaxis and sporozoites–immunized unprotected (gray symbols) individual from group 1 (exposed to bites from 15 infected mosquitoes on three occasions; dots), group 2 (exposed to bites from 10 infected and 5 uninfected mosquitoes on three occasions; triangles), or group 3 (exposed to bites from 5 infected and 10 uninfected mosquitoes on three occasions; squares). Horizontal bars and whiskers represent means and standard errors of the mean (SEM). Panels show CD107a⁺ CD4 T cells (A), CD8 T cells (B), and γδ T cells (C); granzyme B expression by CD4 T cells (D), CD8 T cells (E), and γδ T cells (F); and interferon γ (IFN-γ) expression by CD4 T cells (G), CD8 T cells (H), and γδ T cells (I). Values are corrected for uninfected red blood cell (uRBC) background and for baseline response before immunization. Mean background responses (±SEM) to uRBC stimulation for CD4, CD8, and γδ T cells were 0.19 ± 0.01, 0.41 ± 0.02, and 0.61 ± 0.05, respectively, for CD107a; 1.65 ± 0.50, 15.34 ± 1.46, and 64.56 ± 1.74, respectively, for granzyme B; and 0.09 ± 0.00, 0.07 ± 0.00, and 0.14 ± 0.01, respectively, for IFN-γ (calculated for all volunteers at both baseline and C − 1). High uRBC granzyme B responses in CD8 and γδ T cells indicate that a significant percentage of these cells contain granzyme B even in a resting situation. uRBC responses did not change significantly from baseline for any of the readouts. The differences between responses of protected and unprotected volunteers that are not indicated with a P value are nonsignificant. The differences between protected and unprotected volunteers were evaluated using logistic regression.