Toxoplasma gondii infection triggers a potent IL-12 response in the absence of Toll-like receptor adaptor molecule MyD88

Heather Mercer, Master's Student, Biology

Description

Toxoplasma gondii is an opportunistic pathogen whose control is critically dependent upon the Th1-inducing cytokine IL-12. A major innate immune recognition pathway in mice involves sensing of Toxoplasma by Toll-like receptors (TLR) 11 and 12, which then signal through adaptor molecule MyD88 to instruct dendritic cell IL-12 production. Yet, in humans both TLR11 and TLR12 are nonfunctional and populations genetically deficient in MyD88 show no evidence of increased susceptibility to many microbial infections, including T. gondii. We hypothesize there is an alternate IL-12 pathway that proceeds independently of MyD88. To address this hypothesis, we measured parasite-triggered IL-12 production in wild-type (WT) and MyD88 knockout (KO) mice. Accordingly, we collected splenocytes from WT and KO mice, incubated with Toxoplasma tachyzoites then measured IL-12 release. While there was robust Toxoplasma-induced IL-12 production in WT splenocytes, this response was completely dependent upon functional MyD88. We subsequently infected WT and KO mice by intraperitoneal inoculation with high (RH strain) and low (PTG strain) virulence Toxoplasma, collected peritoneal exudate cells (PEC) 4 days later, then measured ex vivo IL-12 production. In this case, WT and KO PEC from RH infected mice produced equivalent amounts of IL-12. For the case of PTG, WT PEC produced lower amounts of IL-12, and this response was partially dependent upon MyD88. Our results identify an MyD88-independent route of IL-12 production triggered by Toxoplasma, and they further reveal a role for parasite strain in activation of this pathway.

 
Nov 8th, 12:30 PM Nov 8th, 1:30 PM

Toxoplasma gondii infection triggers a potent IL-12 response in the absence of Toll-like receptor adaptor molecule MyD88

Bobo Room, Hodgin Hall, Third Floor

Toxoplasma gondii is an opportunistic pathogen whose control is critically dependent upon the Th1-inducing cytokine IL-12. A major innate immune recognition pathway in mice involves sensing of Toxoplasma by Toll-like receptors (TLR) 11 and 12, which then signal through adaptor molecule MyD88 to instruct dendritic cell IL-12 production. Yet, in humans both TLR11 and TLR12 are nonfunctional and populations genetically deficient in MyD88 show no evidence of increased susceptibility to many microbial infections, including T. gondii. We hypothesize there is an alternate IL-12 pathway that proceeds independently of MyD88. To address this hypothesis, we measured parasite-triggered IL-12 production in wild-type (WT) and MyD88 knockout (KO) mice. Accordingly, we collected splenocytes from WT and KO mice, incubated with Toxoplasma tachyzoites then measured IL-12 release. While there was robust Toxoplasma-induced IL-12 production in WT splenocytes, this response was completely dependent upon functional MyD88. We subsequently infected WT and KO mice by intraperitoneal inoculation with high (RH strain) and low (PTG strain) virulence Toxoplasma, collected peritoneal exudate cells (PEC) 4 days later, then measured ex vivo IL-12 production. In this case, WT and KO PEC from RH infected mice produced equivalent amounts of IL-12. For the case of PTG, WT PEC produced lower amounts of IL-12, and this response was partially dependent upon MyD88. Our results identify an MyD88-independent route of IL-12 production triggered by Toxoplasma, and they further reveal a role for parasite strain in activation of this pathway.