Differential intra-epithelial lymphocyte phenotypes following Cryptosporidium parvum challenge in susceptible and resistant athymic strains of mice

Deciphering Host-Pathogen Interactions: Role of Cryptosporidium in Tumorigenesis

Cryptosporidium, a protozoan parasite affecting the gastrointestinal system, is primarily known for causing diarrhea, especially in those with weakened immune systems. However, there is increasingly persuasive evidence that it may be directly involved in tumorigenesis. This review examines some of the potential mechanisms through which Cryptosporidium infections can induce cancer, specifically chronic inflammation, manipulation of the immune system, and alteration of cell signaling pathways. Persistent inflammation with immune system changes due to chronic infection, particularly among immunocompromised hosts, leads to a microenvironment that facilitates tumorigenesis. Cryptosporidium manipulates important cellular pathways such as PI3K, NF-κB, Wnt, and p38/MAPK to promote cell survival, regulate immune responses, and foster tissue remodeling, all of which contribute to a tumor-friendly microenvironment. Moreover, Cryptosporidium virulence factors such as ROP1, sPLA2, and microRNAs disrupt host cellular stability and significantly alter host cellular gene expression, which also exacerbates inflammation and tissue damage. Epidemiological data have indicated higher rates of Cryptosporidium infection in cancer patients, especially patients with gastrointestinal cancers. This, among other observations, raises the possibility that the infection may be connected to cancer progression. In animal models, especially studies with C. parvum-challenged rodents, chronic inflammation, immune repression, and genetic mutations related to neoplasia have been reported. While this has provided us with valuable information, we still have a long way to go to fully understand the long-term ramifications of Cryptosporidium infection. These cover aspects such as the contribution of latent infections and the genetic diversity of Cryptosporidium strains in cancer. Further investigation is urgently needed to understand the molecular processes by which Cryptosporidium might contribute to carcinogenesis and explore potential strategies for therapy and prevention especially among immunocompromised populations.

IFN-gamma-producing dendritic cells are important for priming of gut intraepithelial lymphocyte response against intracellular parasitic infection

The importance of intraepithelial lymphocytes (IEL) in immunoprotection against orally acquired pathogens is being increasingly recognized. Recent studies have demonstrated that Ag-specific IEL can be generated and can provide an important first line of defense against pathogens acquired via oral route. However, the mechanism involved in priming of IEL remains elusive. Our current study, using a microsporidial model of infection, demonstrates that priming of IEL is dependent on IFN-gamma-producing dendritic cells (DC) from mucosal sites. DC from mice lacking the IFN-gamma gene are unable to prime IEL, resulting in failure of these cells to proliferate and lyse pathogen-infected targets. Also, treatment of wild-type DC from Peyer's patches with Ab to IFN-gamma abrogates their ability to prime an IEL response against Encephalitozoon cuniculi in vitro. Moreover, when incubated with activated DC from IFN-gamma knockout mice, splenic CD8(+) T cells are not primed efficiently and exhibit reduced ability to home to the gut compartment. These data strongly suggest that IFN-gamma-producing DC from mucosal sites play an important role in the generation of an Ag-specific IEL response in the small intestine. To our knowledge, this report is the first demonstrating a role for IFN-gamma-producing DC from Peyer's patches in the development of Ag-specific IEL population and their trafficking to the gut epithelium.

Role of CD8+ and CD4+ T lymphocytes in jejunal mucosal injury during murine giardiasis

T-cell-mediated pathogenesis has been documented in various idiopathic and microbially induced intestinal disorders. Diffuse microvillous shortening seen in giardiasis is responsible for disaccharidase insufficiencies and malabsorption of electrolytes, nutrients, and water. Other mucosal changes include crypt hyperplasia and increased numbers of intraepithelial lymphocytes (IEL). A recent report using an athymic mouse model of infection showed that these epithelial injuries were dependent on T cells. The aim of the present study was to identify which subset of superior mesenteric lymph node (SMLN) T cells were responsible for mucosal alterations in giardiasis. CD4+ and CD8+ T cells, as well as whole lymphocyte populations, were isolated from SMLN of Giardia muris-infected mice for adoptive transfer. Jejunal segments of recipient mice were assessed for brush border ultrastructure, sucrase activity, crypt/villus ratio, and IEL numbers. Mice that received enriched CD8+ and whole SMLN lymphocytes, but not CD4+ T cells, from infected donors showed diffuse shortening of microvilli, loss of brush border surface area, impaired sucrase activity, and increased crypt/villus ratios compared to respective controls. Transfer of whole SMLN lymphocytes, as well as enriched CD4+ or CD8+ T cells, from infected donors led to increased IEL numbers in the recipient jejunum. The findings indicate that loss of intestinal brush border surface area, reduced disaccharidase activities, and increased crypt/villus ratios in giardiasis are mediated by CD8+ T cells, whereas both CD8+ and CD4+ SMLN T cells regulate the influx of IEL.

Recent advances in cryptosporidiosis: the immune response

An increased understanding of host immune responses to Cryptosporidium parvum which are responsible for clearance of primary infection and resistance to reinfection, and characterization of the parasite molecules to which they are directed, are essential for discovery of effective active and passive immunization strategies against cryptosporidiosis. In this article, recent advances in knowledge of humoral and cellular immune responses to C. parvum, their antigen specificities, and mechanisms of protection are briefly reviewed.

Role of gamma interferon in chemokine expression in the ileum of mice and in a murine intestinal epithelial cell line after Cryptosporidium parvum infection

Cryptosporidium parvum is a protozoan parasite that infects intestinal epithelial cells and induces inflammation of the intestine. To better understand the inflammatory process occurring during cryptosporidiosis, we investigated in this study the kinetics of chemokine expression in the mucosa of mice by quantitative reverse transcription-PCR. Our results demonstrate that among the chemokine mRNAs studied, gamma interferon (IFN-gamma)-inducible protein 10 (IP-10), monokine induced by IFN-gamma (MIG), i-TAC, lymphotactin, macrophage inflammatory protein 1 beta (MIP-1 beta), and RANTES mRNAs were strongly up-regulated in infected neonate mice, which correlated with the immunofluorescence staining results showing T-cell and macrophage infiltration in the mucosa. Our in vitro data showed that intestinal epithelial cells infected by C. parvum or stimulated by the proinflammatory cytokines (IFN-gamma, interleukin-1 beta, and tumor necrosis factor alpha) produce a pattern of chemokine secretion similar to that observed in vivo, suggesting that these cells may take part in the initial production of chemokines. In order to identify the chemokines responsible for the recruitment of the inflammatory cells leading to a protective immune response, we compared the patterns of chemokine expression in a healing neonate mouse model and a nonhealing IFN-gamma knockout (GKO) mouse model of cryptosporidiosis. In the absence of IFN-gamma, the chemokine response was altered for IP-10, MIG, i-TAC, RANTES, and MIP-1 beta mRNAs, while the three ELR C-X-C chemokine mRNAs studied (lipopolysaccharide-induced C-X-C chemokine, MIP-2 alpha, and KC mRNAs) were strongly overexpressed. These results are consistent with the neutrophil recruitment observed in the lamina propria of GKO mice at day 9 postinfection but are not consistent with the hypothesis that these cells play an important role in the resolution of the infection. On the contrary, the altered response of chemokines responsible for the recruitment of macrophages and T cells in GKO mice suggests that these two populations may be critical in the development of a protective immune response.

Efficacy of monoclonal antibodies against defined antigens for passive immunotherapy of chronic gastrointestinal cryptosporidiosis

Cryptosporidium parvum is an important cause of diarrhea in humans and calves and can persistently infect immunocompromised hosts. Presently, there are no consistently effective parasite-specific drugs for cryptosporidiosis. We hypothesized that neutralizing monoclonal antibodies (MAbs) targeting the apical complex and surface antigens CSL, GP25-200, and P23 could passively immunize against cryptosporidiosis. We recently reported that a formulation of MAbs 3E2 (anti-CSL), 3H2 (anti-GP25-200), and 1E10 (anti-P23) provided significant additive prophylactic efficacy over that of the individual MAbs in neonatal ICR mice. In the present study, these MAbs were evaluated for therapeutic efficacy against persistent infection in adult gamma interferon-depleted SCID mice. 3E2 demonstrated the most significant and consistent therapeutic effect, reducing intestinal infection in two experiments. In one experiment, 3E2 plus 3H2 and 3E2 plus 3H2 plus 1E10 also significantly reduced infection; however, no significant increase in efficacy over 3E2 alone was apparent. The results indicate that anti-CSL MAb 3E2 has highly significant efficacy in reducing, but not eliminating, persistent C. parvum infection.