Systemic and Mucosal Responses to Oral Administration of Excretory and Secretory Antigens fromGiardia intestinalis

Abstract

Giardia, a flagellated protozoan that infects the upper small intestine of its vertebrate host, is the most common parasitic protist responsible for diarrhea worldwide. Molecules released by the parasite, particularly excretory and secretory antigens, seemed to be associated with pathogenesis as well as with the expression of Giardia virulence. In the present work, we examined the effect of oral administration of Giardia intestinalis excretory and secretory antigens on systemic and local antibody response as well as on mucosal injuries in BALB/c mice. Significant titers of serum-specific immunoglobulin G1 (IgG1) and specific IgG2a were observed. Systemic and mucosal specific IgA antibodies were also recorded. A transient production of serum-specific IgE antibody and high total IgE levels were also detected, suggesting the presence in excretory and secretory proteins of factors promoting a specific IgE response. The sera of excretory and secretory antigen-treated mice recognized proteins of 50 and 58 kDa as well as electrophoretic bands of 15, 63, and 72 kDa that could support a proteinase activity. The in vitro exposure of G. intestinalis trophozoites to heat-inactivated sera from mice orally inoculated with excretory and secretory antigens induced a decrease of growth, revealing a complementindependent inhibitory activity of specific serum antibodies. Furthermore, histological evaluation performed on the small and large intestines revealed moderate to acute histological changes comparable to those observed in natural or experimental Giardia infection characterized by eosinophilic infiltration, hypercellularity, and enterocytic desquamation. The present results suggested that Giardia excretory and secretory antigens stimulate a preferential Th2 response, which is probably involved in the intestinal alterations associated with giardiasis. Giardia intestinalis (synonymous with Giardia lamblia andGiardia duodenalis) is a common causative agent of diarrhea disease occurring in humans and various mammal species (1). This parasite has a worldwide distribution, and its prevalence varies from 15 to 30% in developing countries (26). The infection has been shown to be more prevalent in children less than 3 years of age as well as in undernourished and immunocompromised hosts (5). Moreover, previous studies have also showed that Giardia infection induces a mucosal immune response to other allergens (13) and may be related to an increased incidence of urticaria and food allergies (10). The pathogenesis of giardiasis is not clearly understood, but villous atrophy and reduction of the absorptive area of the small intestine have been reported, which result from a brush border enzyme deficiency responsible for malabsorption (6). Studies in vitro and in vivo have suggested that the parasite is able to produce toxin(s) (3, 8), but the factors inducing mucosal alterations in Giardia infection have not been identified yet, and at this point they are still controversial (12). It has been suggested that excretory and secretory (E/S) ...

Giardia duodenalis: analysis of secreted proteases upon trophozoite-epithelial cell interaction in vitro

“…This is supported by similar observations in previous reports with other substrates and the P1 strain (Hare et al 1989, Parenti 1989. Mining of the Giardia Genome Project based on a clone (A6) from WB strain (http://www.embl.edu/Giardia) revealed at least 7 well characterized genes for giardial cysteine proteases while the deduced open reading frames for other putative proteases predicted only serine and metallo but not aspartic-type proteases.Our findings are also consistent with the detection of proteolytic activity in E/S products from trophozoites of the P1 strain (Jiménez et al 2000(Jiménez et al , 2004. However an enhancement of protease secretion during trophozoites-IEC6 interaction has not been previously reported.…”

“…In addition, the presence of cysteine protease activities in excretory/secretory (E/S) products of P1 strain has also been reported (Jiménez et al 2000). These E/S products are associated with mucosal injuries observed in murine giardiasis (Jiménez et al 2004). However the possible relation between protease secretion and the adhesion of G. duodenalis to epithelial cells has not been tested.…”

Release of metabolic enzymes by Giardia in response to interaction with intestinal epithelial cells

“…It is possible that these fragments interfered with the identification of the 58 kDa protein. Moreover, several unknown proteins with masses ranging from 15 to 225 kDa as well as unidentified proteins with cysteine-type protease activity have been reported in supernatants of Giardia-host cell co-cultures [15,33,34]. This is the first time giardial ADI, OCT and enolase have been shown to be present in Giardia culture supernatants.…”

Microvesicles released from Giardia intestinalis disturb host-pathogen response in vitro

“…A previous study also demonstrated that the excretory-secretory products (ESP) of G. lamblia contained major antigen(s) responsible for protection against infection in mice ( Kaur et al, 1999Kaur et al, , 2001. Oral administration of G. lamblia ESPs into BALB/c mice stimulated a Th2 response, which led to intestinal histological changes characterized by eosinophilic infiltration, and can induce host cell apoptosis, hypercellularity, and enterocytic desquamation (Jiménez et al, 2004). Glycoproteins in G. lamblia ESP were found to induce antibody production during giardiasis (Jiménez et al, 2007).…”

“…Most likely, mechanical effects, or some other, as yet not described mechanism, produces villus and brush border microvillus atrophy, leading to digestive enzyme deficiencies (Solaymani-Mohammadi and Singer, 2011), and chronic giardiasis can lead to mucosal inflammation with pronounced villus loss (Hanevik et al, 2007); protease activities may be a direct cause of diarrhoeas in giardiasis. Moreover, Jiménez et al (2004) found that excretory and secretory antigens (E/S Ags) from G. lamblia induced an intestinal pathogenesis, which coincided with mucosal inflammation in BALB/c mice. Oral administration of the E/S Ags not only stimulated production of antibodies with parasiticidal activity, but also resulted in histological alterations within the intestinal tissue that were comparable to those observed in natural and experimental Giardia infections (Jiménez et al, 2014).…”