Adaptive Immunity, Autophagy Figure 1. CD402/2 mice are susceptible to the chronic phase of T. gondii infection. B6 and CD402/2 mice were infected with tissue cysts of the ME49 strain of T. gondii. A, Survival was monitored daily. Data shown are from groups containing 8 mice. B–I, B6 and CD402/2 mice were euthanized at 4 weeks post-infection. B, Eyes from infected B6 mice revealed mild histopathology. C–E, Eyes from infected CD402/2 mice revealed disruption of retinal architecture, more prominent inflammation (C), invasion of the retina by retinal pigmented epithelial cells (D) and occasional tissue cysts (E). Periodic Acid Schiff-Hematoxylin (PASH); B, C X200; D X400; E X1,000. F, CD402/2 mice exhibit higher parasite load in the eye than B6 mice. DNA was isolated from eyes. Levels of the T. gondii B1 gene were examined using quantitative PCR. Each group contained 5 mice. Results are shown as the mean 6 SEM. G, Brains from infected B6 mice showed slight inflammation. H, Brains from infected CD402/2 mice show prominent areas of inflammation (arrow) and numerous tissue cysts (arrow head). PASH X100. I, CD402/2 mice exhibit higher numbers of tissue cysts in the brain than B6 mice. Each group contained 5 mice. Results are representative of 4 independent experiments. *#0.05; ***p#0.001. doi:10.1371/journal.pone.0014472.g001 parasitophorous vacuole [13]. We further determined whether the mechanism of anti-microbial activity triggered by CD40 is distinct from that utilized by IFN-c. Figure S3A shows that CD40 induced anti-microbial activity against not only a type I strain of T. gondii (RH) but also against a type II strain (ME49). Knockdown of Beclin 1 ablated the anti-T. gondii activity against a type II strain of the parasite induced by CD40 but had no effect on anti-T. gondii activity mediated by IFN-c (Figure S3B). Importantly, knockdown of Irga6 did not impair CD40-induced killing of T. gondii while it inhibited the effect of IFN-c (Figure S3C). Taken together, these studies indicate that CD40 induces entrapment of T. gondii by autophagosomes and triggers anti-T. gondii activity in retinal and brain microglia through the autophagy pathway, a process that is distinct from that utilized by IFN-c since CD40 not only acts PLoS ONE | www.plosone.org 3 December 2010 | Volume 5 | Issue 12 | e14472