TLR9-Dependent Induction of Intestinal α-Defensins by Toxoplasma gondii

Abstract

α-Defensins (or Cryptdins [Crps]) are a group of antimicrobial peptides produced as a component of Paneth cell (PC) secretory granules in the small intestine. In vivo ligation of TLR9 by synthetic agonists leads to PC degranulation, although the mechanism by which this occurs remains uncertain. In this report, we investigated TLR9-dependent mechanisms, triggered by the parasite Toxoplasma gondii, inducing Crp release in the lumen. Oral challenge of C57BL/6J (B6) wild-type (WT) mice with T. gondii induced TLR9 mRNA upregulation associated with a marked increase of type I IFN mRNA expression. PC secretory granules were released, and Crp-3/-5 mRNA expression by purified epithelial cells was increased following oral challenge of B6 WT mice. Although PCs failed to degranulate in infected B6 TLR9−/− mice, i.p. injection of mouse IFN-β alone led to Crp-3/-5 mRNA upregulation in B6 WT and TLR9−/− mice. In addition, modulation of Crp mRNA expression in response to T. gondii infection was abrogated in B6 IFNAR−/− mice, which lack a functional type I IFN receptor. Taken together, these data demonstrate that T. gondii induces Crp-3/-5 production and release by PCs via a TLR9-dependent production of type I IFNs. Crps have a limited direct effect against T. gondii but may indirectly affect the early control of T. gondii invasiveness by promoting the initiation of a protective Th1 response against the parasite.

Strain-Specific Polymorphisms in Paneth Cell α-Defensins of C57BL/6 Mice and Evidence of Vestigial Myeloid α-Defensin Pseudogenes

“…Because the Defcr1 to -6 genes have been cloned from 129/SvJ mice in lambda phage (20), sequencing through the gaps in the Celera assembly will identify the position and orientation of the corresponding genes at the locus and provide a more comprehensive annotation than was possible for this study. The genomic and proteomic differences between ␣-defensins of C57BL/6 and other reference strains may be important to consider in studies of innate immune responses to enteric infection (14,24). For example, evidence of Paneth cell ␣-defensin induction or repression based on microarray data or using immune reagents based on mixed-strain assembly peptides and genes may be difficult to interpret for experiments performed on the C57BL/6 genetic background.…”

Efficacy of Cryptdin-2 as an Adjunct to Antibiotics from Various Generations Against Salmonella

“…Mouse enteric alpha-defensins called cryptdins are expressed in the granules of Paneth cells and are secreted into the lumen of intestinal crypts in response to bacterial stimuli [7]. Cryptdins are broad-spectrum AMPs due to their ability to kill various bacteria [8][9][10], parasites [11] and enveloped viruses [12] in vitro.…”

In VitroandIn VivoSynergistic Effects of Cryptdin 2 and Ampicillin against Salmonella

“…Among naturally occurring AMPs, defensins form a unique family of cysteinerich cationic polypeptides with 3 or 4 disulfide bridges (22,39). Mouse enteric alpha-defensins called cryptdins are broad-spectrum AMPs due to their ability to kill various bacteria (8,12,14,23,28), parasites (9), and enveloped viruses (35) in vitro. Recently, we demonstrated that cryptdin 2 possesses a strong in vivo therapeutic potential against murine salmonellosis without exhibiting any toxicity as indicated by liver and kidney function tests (29).…”