Α1-giardin based live heterologous vaccine protects against Giardia lamblia infection in a murine model.

Giardia lamblia is a leading protozoan cause of diarrheal disease worldwide, yet preventive medical strategies are not available. A crude veterinary vaccine has been licensed for cats and dogs, but no defined human vaccine is available. We tested the vaccine potential of three conserved antigens previously identified in human and murine giardiasis, α1-giardin, α-enolase, and ornithine carbamoyl transferase, in a murine model of G. lamblia infection. Live recombinant attenuated Salmonella enterica Serovar Typhimurium vaccine strains were constructed that stably expressed each antigen, maintained colonization capacity, and sustained total attenuation in the host. Oral administration of the vaccine strains induced antigen-specific serum IgG, particularly IgG(2A), and mucosal IgA for α1-giardin and α-enolase, but not for ornithine carbamoyl transferase. Immunization with the α1-giardin vaccine induced significant protection against subsequent G. lamblia challenge, which was further enhanced by boosting with cholera toxin or sublingual α1-giardin administration. The α-enolase vaccine afforded no protection. Analysis of α1-giardin from divergent assemblage A and B isolates of G. lamblia revealed >97% amino acid sequence conservation and immunological cross-reactivity, further supporting the potential utility of this antigen in vaccine development. Together. These results indicate that α1-giardin is a suitable candidate antigen for a vaccine against giardiasis.

Synthesis and electrochemistry of 2-ethenyl and 2-ethanyl derivatives of 5-nitroimidazole and antimicrobial activity against Giardia lamblia.

Infections with the diarrheagenic pathogen, Giardia lamblia, are commonly treated with the 5-nitroimidazole (5-NI) metronidazole (Mz), and yet treatment failures and Mz resistance occur. Using a panel of new 2-ethenyl and 2-ethanyl 5-NI derivatives, we found that compounds with a saturated bridge between the 5-NI core and a pendant ring system exhibited only modestly increased antigiardial activity and could not overcome Mz resistance. By contrast, olefins with a conjugated bridge connecting the core and a substituted phenyl or heterocyclic ring showed greatly increased antigiardial activity without toxicity, and several overcame Mz resistance and were more effective than Mz in a murine giardiasis model. Determination of the half-wave potential of the initial one-electron transfer by cyclic voltammetry revealed that easier redox activation correlated with greater antigiardial activity and capacity to overcome Mz resistance. These studies show the potential of combining systematic synthetic approaches with biological and electrochemical evaluations in developing improved 5-NI drugs.

Polymeric immunoglobulin receptor in intestinal immune defense against the lumen-dwelling protozoan parasite Giardia.

The polymeric Ig receptor (pIgR) is conserved in mammals and has an avian homologue, suggesting evolutionarily important functions in vertebrates. It transports multimeric IgA and IgM across polarized epithelia and is highly expressed in the intestine, yet little direct evidence exists for its importance in defense against common enteric pathogens. In this study, we demonstrate that pIgR can play a critical role in intestinal defense against the lumen-dwelling protozoan parasite Giardia, a leading cause of diarrheal disease. The receptor was essential for the eradication of Giardia when high luminal IgA levels were required. Clearance of Giardia muris, in which IgA plays a dominant role, was severely compromised in pIgR-deficient mice despite significant fecal IgA output at 10% of normal levels. In contrast, eradication of the human strain Giardia lamblia GS/M, for which adaptive immunity is less IgA dependent in mice, was unaffected by pIgR deficiency, indicating that pIgR had no physiologic role when lower luminal IgA levels were sufficient for parasite elimination. Immune IgA was greatly increased in the serum of pIgR-deficient mice, conferred passive protection against Giardia, and recognized several conserved giardial Ags, including ornithine carbamoyltransferase, arginine deiminase, alpha-enolase, and alpha- and beta-giardins, that are also detected in human giardiasis. Corroborative observations were made in mice lacking the J chain, which is required for pIgR-dependent transepithelial IgA transport. These results, together with prior data on pIgR-mediated immune neutralization of luminal cholera toxin, suggest that pIgR is essential in intestinal defense against pathogenic microbes with high-level and persistent luminal presence.

Adaptive immunity-dependent intestinal hypermotility contributes to host defense against Giardia spp.

Humans infected with Giardia exhibit intestinal hypermotility, but the underlying mechanisms and functional significance are uncertain. Here we show in murine models of giardiasis that small-intestinal hypermotility occurs in a delayed fashion relative to peak parasite burden, is dependent on adaptive immune defenses, and contributes to giardial clearance.