TLR4 Promotes Cryptosporidium parvum Clearance in a Mouse Model of Biliary Cryptosporidiosis

Abstract

Cholangiocytes, the epithelial cells lining intrahepatic bile ducts, express multiple toll-like receptors (TLRs) and thus have the capacity to recognize and respond to microbial pathogens. In previous work we demonstrated that TLR4, which is activated by gram-negative lipopolysaccharide (LPS), is upregulated in cholangiocytes in response to infection with Cryptosporidium parvum in vitro and contributes to NFkB activation. Here, using an in vivo model of biliary cryptosporidiosis we addressed the functional role of TLR4 in C. parvum infection dynamics and hepatobiliary pathophysiology. We observed that C57BL mice clear the infection by three weeks post-infection. In contrast, parasites were detected in bile and stool in TLR4 deficient mice at four weeks post-infection. The liver enzymes, alanine transaminase (ALT) and aspartate transaminase (AST), and the proinflammatory cytokines Tumor Necrosis Factor (TNF)-α, Interferon (IFN)-γ, and Interleukin (IL)-6 peaked at one to two weeks postinfection and normalized by four weeks in infected C57BL mice. C57BL mice also demonstrated increased cholangiocyte proliferation (PCNA staining) at one-week post-infection, which was resolved by two weeks post-infection. In contrast, TLR4 deficient mice showed persistently elevated serum ALT and AST, elevated hepatic IL-6 levels, and histological evidence of hepatocyte necrosis, increased inflammatory cell infiltration, and cholangiocyte proliferation through four weeks post-infection. These data suggest that a TLR4-mediated response is required for efficient eradication of biliary C. parvum infection in vivo, and lack of this pattern recognition receptor contributes to an altered inflammatory response and an increase in hepatobiliary pathology.

Release of Luminal Exosomes Contributes to TLR4-Mediated Epithelial Antimicrobial Defense

“…Consistent with our previous results [35], a higher biliary infection burden was found in TLR4-deficient mice compared with the wild-type animals (Figure 2A). Intriguingly, abundant exosomes were detected in the lumen of the biliary tract from the wild-type animals following infection (Figure 2B and 2C).…”

Protein Malnutrition Impairs Intestinal Epithelial Cell Turnover, a Potential Mechanism of Increased Cryptosporidiosis in a Murine Model

“…Besides inducing epithelial apoptosis, an increase in epithelial cell proliferation was also found after C. parvum infection in the present model, which is consistent with previous reports in the literature (35, 36). Increasing both cell shedding and proliferation in intestinal epithelial cells indicated a defensive response of host to C.…”

Identification and Immunological Characterization of Three Potential Vaccinogens against Cryptosporidium Species

“…Several Toll-like receptors (TLRs) are associated with protection against infection (2,24,25,41). The adaptive immune response to Cryptosporidium is characterized as a T-helper 1 (Th1) response with significant contribution of IL-12, IL-18, IL-23, and gamma interferon (IFN-␥) to the clearance of infection (8).…”