Cryptosporidium muris in adult mice: adoptive transfer of immunity and protective roles of CD4 versus CD8 cells

Immunity to Cryptosporidium: insights into principles of enteric responses to infection

Cryptosporidium parasites replicate within intestinal epithelial cells and are an important cause of diarrhoeal disease in young children and in patients with primary and acquired defects in T cell function. This Review of immune-mediated control of Cryptosporidium highlights advances in understanding how intestinal epithelial cells detect this infection, the induction of innate resistance and the processes required for activation of T cell responses that promote parasite control. The development of a genetic tool set to modify Cryptosporidium combined with tractable mouse models provide new opportunities to understand the principles that govern the interface between intestinal epithelial cells and the immune system that mediate resistance to enteric pathogens.

Commensal Cryptosporidium colonization elicits a cDC1-dependent Th1 response that promotes intestinal homeostasis and limits other infections

Cryptosporidium can cause severe diarrhea and morbidity, but many infections are asymptomatic. Here, we studied the immune response to a commensal strain of Cryptosporidium tyzzeri (Ct-STL) serendipitously discovered when conventional type 1 dendritic cell (cDC1)-deficient mice developed cryptosporidiosis. Ct-STL was vertically transmitted without negative health effects in wild-type mice. Yet, Ct-STL provoked profound changes in the intestinal immune system, including induction of an IFN-γ-producing Th1 response. TCR sequencing coupled with in vitro and in vivo analysis of common Th1 TCRs revealed that Ct-STL elicited a dominant antigen-specific Th1 response. In contrast, deficiency in cDC1s skewed the Ct-STL CD4 T cell response toward Th17 and regulatory T cells. Although Ct-STL predominantly colonized the small intestine, colon Th1 responses were enhanced and associated with protection against Citrobacter rodentium infection and exacerbation of dextran sodium sulfate and anti-IL10R-triggered colitis. Thus, Ct-STL represents a commensal pathobiont that elicits Th1-mediated intestinal homeostasis that may reflect asymptomatic human Cryptosporidium infection.

Lessons Learned from Protective Immune Responses to Optimize Vaccines against Cryptosporidiosis

In developing countries, cryptosporidiosis causes moderate-to-severe diarrhea and kills thousands of infants and toddlers annually. Drinking and recreational water contaminated with Cryptosporidium spp. oocysts has led to waterborne outbreaks in developed countries. A competent immune system is necessary to clear this parasitic infection. A better understanding of the immune responses required to prevent or limit infection by this protozoan parasite is the cornerstone of development of an effective vaccine. In this light, lessons learned from previously developed vaccines against Cryptosporidium spp. are at the foundation for development of better next-generation vaccines. In this review, we summarize the immune responses elicited by naturally and experimentally-induced Cryptosporidium spp. infection and by several experimental vaccines in various animal models. Our aim is to increase awareness about the immune responses that underlie protection against cryptosporidiosis and to encourage promotion of these immune responses as a key strategy for vaccine development. Innate and mucosal immunity will be addressed as well as adaptive immunity, with an emphasis on the balance between T_H1/T_H2 immune responses. Development of more effective vaccines against cryptosporidiosis is needed to prevent Cryptosporidium spp.-related deaths in infants and toddlers in developing countries.

The early intestinal immune response in experimental neonatal ovine cryptosporidiosis is characterized by an increased frequency of perforin expressing NCR1(+) NK cells and by NCR1(-) CD8(+) cell recruitment

Cryptosporidium parvum, a zoonotic protozoan parasite, causes important losses in neonatal ruminants. Innate immunity plays a key role in controlling the acute phase of this infection. The participation of NCR1+ Natural Killer (NK) cells in the early intestinal innate immune response to the parasite was investigated in neonatal lambs inoculated at birth. The observed increase in the lymphocyte infiltration was further studied by immunohistology and flow cytometry with focus on distribution, density, cellular phenotype related to cytotoxic function and activation status. The frequency of NCR1+ cells did not change with infection, while their absolute number slightly increased in the jejunum and the CD8+/NCR1- T cell density increased markedly. The frequency of perforin+ cells increased significantly with infection in the NCR1+ population (in both NCR1+/CD16+ and NCR1+/CD16- populations) but not in the NCR1-/CD8+ population. The proportion of NCR1+ cells co-expressing CD16+ also increased. The fraction of cells expressing IL2 receptor (CD25), higher in the NCR1+/CD8+ population than among the CD8+/NCR1- cells in jejunal Peyer’s patches, remained unchanged during infection. However, contrary to CD8+/NCR1- lymphocytes, the intensity of CD25 expressed by NCR1+ lymphocytes increased in infected lambs. Altogether, the data demonstrating that NK cells are highly activated and possess a high cytotoxic potential very early during infection, concomitant with an up-regulation of the interferon gamma gene in the gut segments, support the hypothesis that they are involved in the innate immune response against C. parvum. The early significant recruitment of CD8+/NCR1- T cells in the small intestine suggests that they could rapidly drive the establishment of the acquired immune response.

New concepts in diagnostics for infectious diarrhea

Conventional approaches to the diagnosis of infectious diarrhea must include several modalities to detect an array of potential viruses, bacteria, and parasites. We will provide a general overview of the wide range of diagnostic modalities available for enteropathogens, briefly discuss some of the limitations of conventional methods, and then focus on new molecular methods, including real-time PCR and next-generation sequencing. In particular, we will discuss quantitation of pathogen load with these techniques. We will then describe examples whereby novel diagnostics may help illuminate the etiology of infectious diarrhea, where they may not, and how they may benefit studies of immunity to enteric infections.

Infectivity of Cryptosporidium andersoni Kawatabi type relative to the small number of oocysts in immunodeficient and immunocompetent neonatal and adult mice

Cryptosporidium andersoni is a protozoan parasite found in many countries that invades the stomachs of primarily adult cattle. Unlike the isolates of C. andersoni in cattle from other countries, C. andersoni isolates from Japanese cattle can infect mice and were identified as a novel type and later defined as C. andersoni Kawatabi type. The biological characteristics of C. andersoni Kawatabi type have not yet been well documented. In the present study, we assess the infectivity of this type isolate in mice with different immune competence status and age. We found that inoculation of more than 1×10(4) oocysts is needed to establish infection in mature mice irrespective of immune status. All of the infected immunocompetent mice recovered after a patent period of approximately 20days. In immunodeficient mice, the pre-patent period was prolonged compared with that of 1×10(6) oocysts, but the pattern and the maximum shedding measured by the number of oocysts per day were almost identical. In neonatal immunocompetent and immunodeficient mice, inoculation with 1×10(4) to 10(5) oocysts was also needed to establish infection. Our results indicate that there is a threshold of oocysts needed to establish patent infection in the acidic conditions of the stomach.

Fell Pony syndrome: characterization of developmental hematopoiesis failure and associated gene expression profiles

Fell Pony syndrome (FPS) is a fatal immunodeficiency that occurs in foals of the Fell Pony breed. Affected foals present with severe anemia, B cell lymphopenia, and opportunistic infections. Our objective was to conduct a prospective study of potential FPS-affected Fell Pony foals to establish clinical, immunological, and molecular parameters at birth and in the first few weeks of life. Complete blood counts, peripheral blood lymphocyte phenotyping, and serum immunoglobulin concentrations were determined for 3 FPS-affected foals, 49 unaffected foals, and 6 adult horses. In addition, cytology of bone marrow aspirates was performed sequentially in a subset of foals. At birth, the FPS-affected foals were not noticeably ill and had hematocrit and circulating B cell counts comparable to those of unaffected foals; however, over 6 weeks, values for both parameters steadily declined. A bone marrow aspirate from a 3-week-old FPS-affected foal revealed erythroid hyperplasia and concurrent erythroid and myeloid dysplasia, which progressed to a severe erythroid hypoplasia at 5 weeks of life. Immunohistochemical staining confirmed the paucity of B cells in primary and secondary lymphoid tissues. The mRNA expression of genes involved in B cell development, signaling, and maturation was investigated using qualitative and quantitative reverse transcriptase PCR (RT-PCR). Several genes, including CREB1, EP300, MYB, PAX5, and SPI1/PU.1, were sequenced from FPS-affected and unaffected foals. Our study presents evidence of fetal erythrocyte and B cell hematopoiesis with rapid postnatal development of anemia and B lymphopenia in FPS-affected foals. The transition between fetal/neonatal and adult-like hematopoiesis may be an important aspect of the pathogenesis of FPS.

Cryptosporidiosis: host immune responses and the prospects for effective immunotherapies

Cryptosporidium spp. that develop in intestinal epithelial cells are responsible for the diarrhoeal disease cryptosporidiosis, which is common in humans of all ages and in neonatal livestock. Following infection, parasite reproduction increases for a number of days before it is blunted and then impeded by innate and adaptive immune responses. Immunocompromised hosts often cannot establish strong immunity and develop chronic infections that can lead to death. Few drugs consistently inhibit parasite reproduction in the host, and chemotherapy might be ineffective in immunodeficient hosts. Future options for prevention or treatment of cryptosporidiosis might include vaccines or recombinant immunological molecules, but this will probably require a better understanding of both the mucosal immune system and intestinal immune responses to the parasite.

Evaluation of DNA encoding acidic ribosomal protein P2 of Cryptosporidium parvum as a potential vaccine candidate for cryptosporidiosis

The Cryptosporidium parvum acidic ribosomal protein P2 (CpP2) is an important immunodominant marker in C. parvum infection. In this study, the CpP2 antigen was evaluated as a vaccine candidate using a DNA vaccine model in adult C57BL/6 IL-12 knockout (KO) mice, which are susceptible to C. parvum infection. Our data show that subcutaneous immunization in the ear with DNA encoding CpP2 (CpP2-DNA) cloned into the pUMVC4b vector induced a significant anti-CpP2 IgG antibody response that was predominantly of the IgG1 isotype. Compared to control KO mice immunized with plasmid alone, CpP2-immunized mice demonstrated specific in vitro spleen cell proliferation as well as enhanced IFN-γ production to recombinant CpP2. Further, parasite loads in CpP2 DNA-immunized mice were compared to control mice challenged with C. parvum oocysts. Although a trend in reduction of infection was observed in the CpP2 DNA-immunized mice, differences between groups were not statistically significant. These results suggest that a DNA vaccine encoding the C. parvum P2 antigen is able to provide an effective means of eliciting humoral and cellular responses and has the potential to generate protective immunity against C. parvum infection but may require using alternative vectors or adjuvant to generate a more potent and balanced response.

Some Opportunistic Parasitic Infections in AIDS: Candidiasis, Pneumocystosis, Cryptosporidiosis, Toxoplasmosis

Almost 80% of patients with AIDS die from infections other than human immunodeficiency virus (HIV). These infections usually occur late in the course of disease when CD4(+) T-cell count has fallen below 200 permm(3) cells per milliliter. Most of these infections are caused by organisms that do not normally afflict healthy individuals and are thus considered to be opportunistic. In this article, Lloyd Kasper and Dominique Buzoni-Gatel review the host-parasite interaction for four important pathogens: Candida albicans and Pneumocystis carinii (usually non-invasive pathogens), Cryptosporidium parvum (invades the cells but remains localized in the gut) and Toxoplasma gondii (penetrates through the gut to cause systemic infection). These organisms, which generally cause limited or even insignificant clinical evidence of infection in the normal host, were chosen because of their high prevalence in AIDS patients and because they exhibit different invasive abilities. The reason why individuals with AIDS are susceptible to this particular group of pathogens is uncertain.

Activated CD8+ T cells contribute to clearance of gastric Cryptosporidium muris infections

The role of CD4+ and CD8+ T lymphocytes in the development of a protective immune response against Cryptosporidium muris infection was studied by the reconstitution of severe combined immunodeficient (SCID) mice with well-defined populations of either naive or immune CD8+ or CD4+ T lymphocytes. Adoptive transfer of both naive and immune CD4+ T lymphocyte subpopulations protects SCID mice against cryptosporidiosis. Moreover, a significant biological impact of activated CD8+ T cells against gastric cryptosporidiosis was observed. The significant difference in the course and intensity of the infection in reconstituted SCID mice was found to be dependent on the protective function of both the CD4+ and CD8+ T-cell populations transferred. While SCID mice reconstituted with either immune or naive CD4+ or immune CD8+ T-cell subpopulations resolved the infection within 29, 37 and 51 days post-infection, respectively, those reconstituted with naive CD8+ T cells suffered from chronic infection similar to control SCID mice. Reconstitution with CD4+ T cells resulted in suppression of oocyst excretion and shortening of patent period in comparison with SCID mice reconstituted with CD8+ T cells. Thus, although CD4+ T cells are considered important in protective immunity, our results are the first to demonstrate the involvement of activated CD8+ T lymphocytes in the protection of mice against gastric cryptosporidiosis.

Activation of protective cell-mediated immune response in gastric mucosa during Cryptosporidium muris infection and re-infection in immunocompetent mice

Gastric cryptosporidia only inhabit the glandular part of the stomach of all age categories of their hosts and can cause chronic life-long infections independent of a host's immune status. The immune response in the stomach mucosa during the primary infection and re-infection with Cryptosporidium muris (TS03 and CB03) in immunocompetent BALB/c mice was characterized using flow cytometry analysis and measurement of IFN-gamma and IL10 by enzyme-linked immunosorbent assays (ELISA). Significantly, elevated migration of T lymphocytes (more than 1,000-fold), especially CD8+ T lymphocytes, to the stomach mucosa occurred during primary infection and persisted for more than 2 months after its resolution. The ex vivo cultures of splenocytes revealed very low levels of IFN-gamma production during the course of the primary infection (0.5 ng/ml), whereas in the following re-exposure to the parasites, the concentration of IFN-gamma rapidly increased 22-fold. Although the two parasite strains that were tested were genetically distinct, they yielded similar results in the induction of cellular immune responses, suggesting that these patterns are not unique to a single parasite strain. These results imply that the CD8+ T lymphocytes are involved in the immune response to gastric cryptosporidiosis and could play an important role in the elimination of C. muris infection in mice.

Cooperative role of macrophages and neutrophils in host Antiprotozoan resistance in mice acutely infected with Cryptosporidium parvum

Severe experimental infections with Cryptosporidium parvum have been reported in immunocompromised animals such as SCID mice (mice without functional T cells and B cells). In a C. parvum infection with 1 x 10(6) oocysts/mouse in SCID beige (SCIDbg) mice (SCID mice lacking functional NK cells), oocyst shedding was first demonstrated 18 days after infection. However, shedding was shown as early as 3 days after the same infection in SCIDbgMN mice. All of the SCIDbgMN mice died within 16 days of C. parvum infection, while 100% of the SCIDbg mice exposed to the parasite survived. SCIDbgMN mice are SCIDbg mice depleted of functional macrophages (Mphi) and neutrophils (PMN), suggesting that the severity early after C. parvum infection is strongly influenced by the functions of Mphi and PMN. All SCIDbgMN mice orally infected with a lethal dose of C. parvum survived after they were inoculated with Mphi from SCIDbg mice exposed to C. parvum (CP-Mphi) or resident Mphi previously cultured with PMN from C. parvum-infected SCIDbg mice (CP-PMN). However, all SCIDbgMN mice inoculated with CP-PMN alone or resident Mphi alone died after C. parvum infection. CP-Mphi were identified as classically activated Mphi (M1Mphi), and CP-PMN were characterized as PMN-I. In in vitro studies, resident Mphi converted to M1Mphi after transwell cultivation with CP-PMN. These results indicate that the resistance of SCIDbg mice early after C. parvum infection is displayed through the function of M1Mphi which are converted from resident Mphi influenced by CP-PMN (PMN-I).

Changes in mouse circulating leukocyte numbers in C57BL/6 mice immunosuppressed with dexamethasone for Cryptosporidium parvum oocyst production

The Iowa strain of Cryptosporidium parvum will not propagate in immunocompetent mice, but will successfully infect genetically immunocompromised nude or SCID mice as well as immunocompetent mice which have been immunosuppressed with glucocorticoids. Using dexamethasone-tetracycline is one published method for immunosuppressing mice for the production of C. parvum oocysts. However, dexamethasone-induced immunosuppression is variable, because it is dependent on the total daily water consumption of each individual mouse. The changes in circulating leukocytes and other immune system associated organs before, during and after dexamethasone suppression were analyzed for comparison with a new single injection methylprednisolone acetate (MPA) suppression model. The dexamethasone-induced immunocompromised state was associated with a greater than 90% sustained drop in circulating T-lymphocytes, a greater than 700% increase in circulating mature segmented neutrophils and a severe depletion of circulating monocytes. The thymus and spleen decreased in size by over 80%. Oocyst shedding in suppressed mice started within 4 days of oocyst inoculation and persisted for 6 days post-dexamethasone treatment. Seven days after dexamethasone withdrawal, circulating neutrophils still were 549% higher than controls. Circulating CD3 and CD4 lymphocytes remained depressed by 85-90% while on dexamethasone and for 7 days after discontinuing dexamethasone. CD8 lymphocyte numbers initially decreased by 90%, but rose even while on dexamethasone and even with severe thymic involution. At day 7 post-dexamethasone treatment, the spleen was 119 mm(3), approximating the same size as controls. Fourteen days post-dexamethasone treatment, which was 8 days after oocyst shedding had ceased, the CD8 counts per 5000 events were only 1.6% below controls, while the CD3 and CD4 counts were still depressed by 66%. The thymus now was about one quarter smaller than the controls. The rise in circulating CD8 lymphocytes, when oocyst production stopped, suggests that CD8 positive lymphocytes may play a significant role in vivo in clearing the parasite. The overall pattern of immunosuppression was nearly identical to that observed with the methylprednisolone acetate immunosuppression model.

Methylprednisolone acetate immune suppression produces differing effects on Cryptosporidium muris oocyst production depending on when administered

At different times after inoculation with Cryptosporidium muris, infected CF-1 female mice were immunosuppressed with a single subcutaneous dose of methylprednisolone acetate (MPA; 600 mg/kg). MPA immunosuppression decreases circulating CD3, CD4 and CD8 T-lymphocytes and B-lymphocytes by greater than 90% for approximately 14 days with numbers not returning to pre-suppression levels until after 41 days post-suppression. Immunosuppression was initiated at selected times before, during, and after oocyst production. Immunosuppression initiated prior to oocyst production delayed the start of production by 4-5 days and extended oocyst shedding by 16 days. Initiation of immunosuppression during oocyst production both extended oocyst shedding and greatly increased the number of oocysts shed per day over most of the extended shedding period. Immunosuppression during the decline of oocyst production resulted in only a moderate extension of shedding and a moderate increase in oocyst numbers. Immunosuppression initiated soon after oocyst shedding had ceased resulted in the re-initiation of limited oocyst production for only a few days. Suppression initiated on days 40 and 46 post-infection, 11 and 17 days after oocysts could no longer be detected in the feces, did not result in a resumption of oocyst production. In all cases, where oocyst production was extended or reinitiated, the shedding of oocysts halted between days 45 and 53 post-oocyst inoculation. These studies demonstrate that the effect of MPA immunosuppression depends on the immunologic conditions existing in the host at the time immunosuppression was initiated. Immunosuppression initiated during oocyst production allows an overwhelming parasitism to exist, implying that T- and B-lymphocytes play an important role in moving the host immune process along during this period of the infection. Conversely, severe suppression of T- and B-lymphocytes initiated as oocyst production is decreasing does not result in a complete relapse of the disease suggesting that T- and B-lymphocytes are not critical to the continuation of the immune process after this point. These studies also show that the C. muris infection persists beyond the end of the detection of oocysts in the feces.

Chemically and genetically immunocompromised mice are not more susceptible than immunocompetent mice to infection with Cryptosporidium muris

The prevailing paradigm is that immunosuppressed individuals are more susceptible to infection and are at higher risk of infection from Cryptosporidium oocysts if present in drinking water. To test this hypothesis, three immune conditions were examined: genetically immunocompromised T cell deficient CD-1 nude mice, B and T cell deficient Fox Chase CB-17/IcrClB SCID mice, and chemically immunosuppressed C57Bl/6 mice. Chemical immunosuppression was induced with a single subcutaneous injection of methylprednisolone acetate (MPA) at 600 mg/kg. The MPA immunosuppressed C57Bl/6 mice were characterized by a sustained decrease in circulating CD3, CD4 and CD8 T-lymphocytes of greater than 80% and a similar decrease in B-lymphocytes. A sharp rise in circulating mature segmented neutrophils followed MPA injection, dropping sharply after 10-14 days, mirroring the decrease in lymphocytes. The cessation of oocyst production after MPA was not accompanied by a radical rise in circulating CD3 or CD4 T-lymphocytes, but rather a rise in CD8 T-lymphocytes. The ID50 for the MPA immunosuppressed C57Bl/6 mice was 122 oocysts, whereas the ID50 for the C57Bl/6 immunocompetent group was 44. The genetically immunocompromised mice showed similar differences. The ID50 for CD-1 nude mice was 166 oocysts compared to 64 in CD-1 immunocompetent mice. For Fox Chase CB-17/IcrClB SCID and the immunocompetent CB-17 mice, the ID50's were 83 and 60 oocysts, respectively. These results suggest that the lack of an immune response does not increase the ability of C. muris to establish a productive infection and produce oocysts.

Changes in immune-related gene expression and intestinal lymphocyte subpopulations following Eimeria maxima infection of chickens

Coccidiosis, a major intestinal parasitic disease of poultry, induces a cell-mediated immune response against the etiologic agent of the disease, Eimeria. In the current study, the expression levels of gene transcripts encoding pro-inflammatory, Th1, and Th2 cytokines, as well as chemokines were measured in intestinal intraepithelial lymphocytes (IELs) after Eimeria maxima infection. In addition, changes in IEL numbers were quantified following E. maxima infection. Transcripts of the pro-inflammatory and Th1 cytokines IFN-gamma, IL-1beta, IL-6, IL-12, IL-15, IL-17, and IL-18 were increased 66- to 8 x 10(7)-fold following primary parasite infection. Similarly, mRNA levels of the Th2 cytokines IL-3, IL-10, IL-13, and GM-CSF were up-regulated 34- to 8800-fold, and the chemokines IL-8, lymphotactin, MIF, and K203 were increased 42- to 1756-fold. In contrast, IFN-alpha, TGF-beta4, and K60 transcripts showed no increased expression, and only the level of the Th2 cytokine IL-13 was increased following secondary E. maxima infection. Increases in intestinal T cell subpopulations following E. maxima infection also were detected. CD3(+), CD4(+), and CD8(+) cells were significantly increased at days 8, 6, and 7 post-primary infection, respectively, but only CD4(+) cells remained elevated following secondary infection. TCR1(+) cells exhibited a biphasic pattern following primary infection, whereas TCR2(+) cells displayed a single peak in levels. Taken together, these data indicate a global chicken intestinal immune response is produced following experimental Eimeria infection involving multiple cytokines, chemokines, and T cell subsets.

Characterization of a single dose methylprednisolone acetate immune suppression model using Cryptosporidium muris and Cryptosporidium parvum

An immunosuppressive dose of methylprednisolone acetate (MPA) was compared with a non-immunosuppressive dose using Cryptosporidium oocyst production as an indicator of immunosuppression. To be classified as immunosuppressive, the dose had to satisfy five criteria. First, the dose had to abrogate normal immune defenses allowing the propagation of an organism to which the host is normally resistant, i.e. Cryptosporidium parvum in adult mice. Second, the dose had to decrease overall circulating CD4 T-lymphocyte numbers by greater than 80%. Third, the immunosuppressive dose had to prolong the infection beyond the normal infection length, and fourth, increase the severity of an active infection. Lastly, after complete recovery from a C. muris infection, immunosuppression must suppress the naturally acquired post infection immunity and allow reinfection. In mice immunosuppression with 600 mgMPA/kg lasted approximately 14 days and satisfied all five criteria. Fecal oocyst production could be perpetuated by dosing at 10-day intervals. A 200 mgMPA/kg dose transiently lowered CD4 counts by over 80%, but failed to override the naturally acquired post infection immunity or allow infection with C. parvum. The immunosuppressed blood profile consisted of an immediate sharp rise of mature segmented neutrophils combined with a severe decrease in circulating T-lymphocyte numbers. The rise and fall of neutrophils proved to be a good indicator of the severity and duration of immunosuppression. The thymus and spleen likewise contracted and then expanded in accordance with the steroid effect. The metabolism of MPA resulted in the eventual recovery of immune function signified by the cessation of C. parvum oocyst production. The recovery blood profile was associated with circulating CD8 counts near control levels, continuing 80% depression of CD4 counts and a dropping total neutrophil count. This study shows that the 600 mg/kg MPA dose is a good model for immunosuppression, which satisfies all five criteria for immunosuppression with low morbidity and low mortality.

Absence of weight loss during Cryptosporidium infection in susceptible mice deficient in Fas-mediated apoptosis

Apoptosis plays a major role in the development of pathogenesis due to a number of microbial infections. Epithelial cells have been previously shown to die through apoptosis during in vitro infection by the Apicomplexan parasite Cryptosporidium parvum. We now test the possibility that Fas (APO-1/CD95)-dependent apoptosis of uninfected cells, due to enhanced expression of the Fas ligand (FasL) on infected cells, may contribute to the pathology of cryptosporidiosis. Expression of the FasL increased by a large amount on the surface of intestinal epithelial cells infected with C. parvum, and the increase was limited exclusively to infected cells. In addition, a significant increase in FasL expression was observed in epithelial cells from the small intestine of mice infected with C. parvum. Finally, whereas wild-type mice depleted of CD4(+) lymphocytes lost weight during C. parvum infection, CD4(+) cell-depleted lpr mice (deficient in Fas function) infected with C. parvum gained weight at the same rate as undepleted wild-type or lpr mice. These results suggest that bystander Fas-dependent apoptosis of uninfected epithelial cells may exacerbate the weight loss associated with cryptosporidiosis.

Cryptosporidium parvum-specific mucosal immune response in C57BL/6 neonatal and gamma interferon-deficient mice: role of tumor necrosis factor alpha in protection

Both neonatal and C57BL/6 gamma interferon (IFN-gamma) knockout (C57BL/6-GKO) mice are susceptible to Cryptosporidium parvum, but the course of infection is different. Neonatal mice are able to clear the parasite within 3 weeks, whereas C57BL/6-GKO mice, depending on age, die rapidly or remain chronically infected. The mechanism by which IFN-gamma leads to a protective immunity is yet poorly understood. In order to investigate the effect of IFN-gamma on other cytokines expressed in the intestinal mucosa during C. parvum infection, we studied cytokine mRNA expression in the neonates and GKO (neonatal and adult) mice by quantitative reverse transcription-PCR (RT-PCR) at 4 and 9 days after infection. IFN-gamma mRNA levels were quickly and strongly up-regulated in the mucosa of neonatal mice. In GKO mice, the Th1-type response was dramatically altered during the infection, whereas the mRNA expression levels of the Th2-type cytokines interleukin 4 (IL-4) and IL-10 were increased in both mouse models. In the absence of IFN-gamma, the adult knockout mice up-regulated the mRNA levels of inflammatory cytokines, such as IL-1beta, IL-6, and granulocyte-macrophage colony-stimulating factor, in the mucosa, but not tumor necrosis factor alpha (TNF-alpha), whereas all these cytokines were up-regulated in the infected neonatal mice. Further experiments indicated that injections of TNF-alpha into GKO adult mice significantly reduced oocyst shedding. The results of the present study indicate that the resolution of infection is dependent on the expression of Th1-type cytokines in the mucosa of C57BL/6 mice and that TNF-alpha may participate in the control of parasite development.

Host cell-mediated responses to infection with Cryptosporidium

The coccidian Cryptosporidium infects epithelial cells of a variety of vertebrate hosts and is the causative agent of cryptosporidiosis. In mammals, including humans and domestic animals, C. parvum infects the gastrointestinal tract producing an acute watery diarrhoea and weight loss. CD4+ T-cell-deficient hosts have increased susceptibility to infection with the parasite and may develop severe life-threatening complications. The host responses which induce protective immunity and contribute to pathogenesis are poorly understood. In the immunological control of infection, recent studies with murine infection models suggest that IFN-gamma plays a key role in a partially protective innate immunity against infection identified in immunocompromised mice and also in the elimination of infection mediated by CD4+ T-cells. At the mucosal level, CD4+ intraepithelial lymphocytes are involved in the control of cryptosporidial infection, acting at least in part through production of IFN-gamma which has a direct inhibitory effect on parasite development in enterocytes. Primary infection of ruminants induces an intestinal inflammatory response in which increased numbers of various T-cell subpopulations appear in the villi. In addition, infection results in increased intestinal expression of pro-inflammatory cytokines such as IL-12, IFN-gamma and TNF-alpha. Because these cytokines appear to be important in the aetiology of inflammatory bowel disease, it is possible that they are involved in the mucosal pathogenesis of cryptosporidiosis.

Adoptive transfer of immunity with intraepithelial lymphocytes in Cryptosporidium parvum-infected severe combined immunodeficient mice

BACKGROUND

Intestinal infections with the protozoan parasite Cryptosporidium parvum are prevalent in both immunocompetent and immunocompromised hosts. Although C parvum is an important cause of outbreaks and opportunistic infections worldwide, little is known about protective mucosal immune responses. This is in part because animal models of infection are limited to those with genetic or induced immunodeficiencies.

METHOD

In this report, we isolated immune (primed) or nonimmune (unprimed) intraepithelial lymphocytes (IEL) from BALB/cJ mouse intestines, adoptively transferred them into C parvum-infected severe combined immunodeficient (SCID) mice, and evaluated infection and cell phenotype responses.

RESULTS

Control SCID mice that received no IEL shed large numbers of oocysts throughout the experimental period (day 18 to day 72). Transfer of primed IEL significantly reduced fecal oocyst shedding in recipient SCID mice compared with SCID mice that received unprimed IEL or no IEL. SCID mice transferred with unprimed IEL shed variable numbers of fecal oocysts that increased and decreased in bursts until day 57 after infection. SCID mice transferred with primed IEL exhibited significantly higher proportions of T-cell receptor (TCR) alphabeta+, CD8+, and CD8alphabeta+ EL compared with inoculated SCID mice that received unprimed or no IEL.

CONCLUSION

We conclude that primed IEL from immunocompetent mice may influence protective mucosal response against cryptosporidiosis when transferred into SCID mice. In addition, the increased percentage of TCR alphabeta+, CD8+, CD8alphabeta+ IEL in recipient SCID mice may reflect mucosal cell populations involved in these responses during chronic C parvum infection.

Eimeria tenella infection induces local gamma interferon production and intestinal lymphocyte subpopulation changes

The role of intestinal lymphocytes and gamma interferon (IFN-gamma) production in protective immunity to Eimeria tenella infection was evaluated in two inbred strains of chickens (SC and TK) that display different patterns of susceptibility to coccidiosis. Oral inoculation of either strain with E. tenella led to parasite invasion of the intestinal cecum and cecal tonsils. Greater fecal oocyst shedding was seen in TK chickens. Flow cytometric analyses of cecal tonsil lymphocytes demonstrated greater numbers of CD4(+) and T-cell receptor gammadelta-positive (TCR1(+)) cells in SC chickens and elevated numbers of CD8(+) and TCR2(+) cells in TK chickens following primary infection. IFN-gamma mRNA expression was significantly increased in cecal tonsil and intraepithelial lymphocytes at days 6 and 8, respectively, after primary infection in SC compared to TK chickens. While no differences were noted between cecal tonsil lymphocytes of the two strains following secondary infection, TK chickens showed elevated IFN-gamma transcript levels in intestinal intraepithelial lymphocytes at this time. Selective depletion of CD4(+), but not CD8(+), cecal tonsil lymphocytes in SC chickens resulted in a reduced IFN-gamma mRNA expression, indicating that CD4(+) cells are the primary source of this cytokine. Collectively, these results indicate that local lymphocyte responses and production of IFN-gamma are influenced by host genetic factors.

Nasal immunization of mice with Cryptosporidium parvum DNA induces systemic and intestinal immune responses

DNA immunization offers a novel approach to inducing humoral and cellular immunity against infectious pathogens. We examined whether such an approach could be used against cryptosporiodiosis, an intestinal disease caused by the protozoan parasite Cryptosporidium parvum. This infection is a major problem for young ruminants and immunosuppressed individuals in whom cryptosporidiosis causes life-threatening symptoms. The life cycle of C. parvum takes place in the enterocytes of the intestinal epithelium. We therefore focused our attention on a route of immunization that might induce a mucosal immunoglobulin (Ig)A response. Eight-week-old BALB/c mice were immunized intranasally with DNA encoding a 15-kDa C. parvum sporozoite antigen (CP15-DNA) cloned onto the plasmid pcDNA3. CP15-DNA-immunized mice developed specific and longlasting production of anti-CP15 Ig A in intestinal secretions and specific IgG in sera 3 months and 1 year after the first DNA inoculation. CP15-DNA-immunized mice also developed an antigen-specific T lymphocyte proliferative response in both spleen and mesenteric lymph nodes. Control mice that received the pcDNA3 plasmid alone did not develop specific humoral and cellular responses. These results indicate that plasmid DNA may provide a powerful means of eliciting intestinal humoral and cellular responses to C. parvum infections in mammals.

Protection of kids against Cryptosporidium parvum infection after immunization of dams with CP15-DNA

In this study the effectiveness of a DNA vaccine to confer protection against cryptosporidiosis, an enteric infection of lifestock and humans, was evaluated. A vaccination protocol using a recombinant plasmid encoding the 15 kDa surface sporozoite protein of Cryptosporidium parvum was developed in adult pregnant goats. The present study reports that nasal immunization of pregnant goats with CP15-DNA led to a transfer of immunity to offspring conferring protection against C. parvum infection. Kids from CP15-DNA-vaccinated dams shed significantly fewer oocysts and over a shorter period than did kids from unvaccinated goats. The low level of parasite development in protected kids did not affect their growth whereas unprotected kids grew much slowly. There was still a significant difference in the weights of protected and unprotected kids after complete recovery. Anti-CP15 antibodies were present in serum and colostrum from vaccinated goats. Nevertheless, the precise immune mechanism of protection has still to be determined. This vaccine should reduce the economic losses due to cryptosporidiosis in ruminants, specially in small ruminants (calves, lambs, kids). It has also the potential to reduce environmental contamination by reducing oocyst shedding.

A Cryptosporidium parvum oocyst low molecular mass fraction evokes a CD4+ T-cell-dependent IFN-gamma response in bovine peripheral blood mononuclear cell cultures

T-Cell antigens that induce the in-vitro interferon-gamma response during Cryptosporidium parvum infection of neonatal calves were identified. A total oocyst extract was separated into a high and a low Mr fraction by a microfiltration technique. Both the high and low Mr fractions evoked an in-vitro interferon-gamma response in naturally infected animals, although strong individual differences between the hosts were observed. Using a complement-mediated technique CD4+ T-cells or WC1+gammadelta T-cells were depleted, whereupon the remaining lymphocyte cultures were stimulated with the different antigen preparations. It was shown that the in-vitro interferon-gamma response of Cryptosporidium-infected calves is CD4+ T-cell-dependent.

Cryptosporidium parvum infection in bovine neonates: dynamic clinical, parasitic and immunologic patterns

Twenty-six experimentally infected calves were monitored daily for oocyst excretion. All began excreting oocysts 3-6 days p.i. Most calves (n = 23) excreted oocysts for 6-9 days, with a daily range from 4 x 10(2) to 4.15 x 10(7) oocysts g(-1) of faeces. Over half the calves excreted peak numbers of oocysts 6-8 days p.i. Diarrhoea, observed intermittently beginning as early as day 3 p.i., lasted 4-16 days and varied greatly in severity from calf to calf. In a second study, nine of 18 calves were orally inoculated with 5 x 10(6) oocysts between birth and 2 days of age and nine remained uninfected. Monoclonal antibodies for cell surface markers indicated substantial increases in CD4+ and CD8+ T cells in the intraepithelial lymphocyte population of the ilea of infected calves at 7-9 days of age. RT-PCR demonstrated increases in mRNA for interleukin-12 and interferon-gamma that correlated with increases in both CD4+ and CD8 + intraepithelial lymphocyte cells. Increased mRNA for interleukin-12 and interferon-gamma from lamina propria lymphocytes correlated with increased numbers of CD8+ cells. No changes were found in interleukin-2, interleukin-4 or interleukin-10 mRNA levels. However, interleukin-15 mRNA, possibly from epithelial cells contaminating intraepithelial lymphocytes, was decreased in infected calves and had a negative correlation with increases in CD4+ and CD8+ cells. No differences were detected in mRNA levels for cytokines from lymph node lymphocytes.

Gut intraepithelial lymphocytes induce immunity against Cryptosporidium infection through a mechanism involving gamma interferon production

Immunological control of infection with cryptosporidia in mice is dependent on CD4+ T cells and the production of gamma interferon (IFN-gamma), but to date, the mucosal T cells which produce IFN-gamma local to the infection have not been characterized. We previously showed that immunity against the gastric parasite Cryptosporidium muris could be adoptively transferred to adult SCID (severe combined immunodeficiency) mice with small intestinal intraepithelial lymphocytes (IEL) from previously infected immunocompetent mice, but only if the donor CD4+ T cells were intact. The present investigation examined whether IFN-gamma was important in the effector mechanisms mediated by immune IEL in SCID mice. The development of resistance against C. muris infection in SCID mice given immune IEL was prevented by treatment with a hamster anti-mouse IFN-gamma-neutralizing monoclonal antibody, but following cessation of antibody treatment, the mice recovered from infection. In further experiments, an enzyme-linked immunospot (ELISPOT) technique was used to compare frequencies of IFN-gamma-producing cells in activated T-cell populations from C. muris-immune and naive donor mice. Stimulation with concanavalin A or a rat anti-mouse CD3 monoclonal antibody resulted in detection of greater numbers of cells producing IFN-gamma from immune than naive IEL populations. Small numbers of IEL from C. muris-immune mice, but not from naive mice, also produced IFN-gamma when cultured with soluble oocyst antigen, but this occurred only if gamma-irradiated spleen cells were cocultured with the immune IEL. These results suggested that IEL were important in the generation of immunity to Cryptosporidium and that one of their crucial functions was to produce IFN-gamma at the site of infection.

Protective responses against skin-dwelling microfilariae of Onchocerca lienalis in severe combined immunodeficient mice

Inoculation of severe combined immunodeficient (SCID) mice with microfilariae of Onchocerca lienalis results in a sustained infection of the skin, extending for months beyond the point at which the parasites are eliminated from immunocompetent BALB/c controls. Reconstitution of SCID mice with spleen cells, thymocytes, or CD4+-cell-enriched splenocytes from naive BALB/c donors confers the ability to mount a protective immune response, leading to the rapid elimination of microfilariae. High levels of interleukin-5 and low levels of gamma interferon in the sera of reconstituted SCID mice during the destruction of microfilariae suggest that this protective immune response is directed by Th2 lymphocytes, mirroring that observed in immunocompetent controls. Unexpectedly, abbreviation of primary infections of unreconstituted SCID mice with the drug ivermectin induces resistance to reinfection with microfilariae at a level equivalent to that induced in secondarily infected, immunocompetent controls. In contrast to protection mediated by adoptive reconstitution, resistance induced by ivermectin-abbreviated infection occurs in the absence of T cells and in association with negligible levels of serum interleukin-5 and gamma interferon. This points to the activation of some alternative host defense mechanism that operates after the clearance of therapeutic levels of drug. Such a response could have important implications for the treatment of human onchocerciasis and may go some way in explaining the long-term suppression of microfilariae observed in patients after treatment with ivermectin.

Localization of alpha/beta and gamma/delta T lymphocytes in Cryptosporidium parvum-infected tissues in naive and immune calves

The nature of the host's T-lymphocyte population within the intestinal villi following Cryptosporidium parvum infection was characterized with a bovine model of cryptosporidiosis. In naive animals, infection with C. parvum resulted in substantial increases in the numbers of alpha/beta T cells, both CD4+ (150%) and CD8+ (60%), and of gamma/delta T cells (70%) present within the intestinal villi of the infected ileum. In immune animals, the host T-lymphocyte response to a challenge infection with C. parvum was restricted to alpha/beta T cells. The number of CD4+ T cells within the Peyer's patch of the ileum increased dramatically; however, there was little change in the number or localization of CD4+ T cells within the intestinal villi. In contrast, the number of CD8+ T cells within the intestinal villi increased following a challenge infection. In addition, the CD8+ T cells were found to be intimately associated with the epithelial cells of the intestinal villi. The precise correlation between the accumulation of CD8+ T cells and the normal site of parasite development suggests an important role for CD8+ T cells in the immune animal.

Parasitic diseases in immunocompromised hosts. Cryptosporidiosis, isosporiasis, and strongyloidiasis

Cryptosporidiosis and isosporiasis are intestinal infections caused by the protozoan parasites Cryptosporidium parvum and Isospora belli, respectively. HIV infection and other immunodeficiency diseases predispose human subjects to severe and prolonged cryptosporidiosis. There is also evidence that HIV infection predisposes to chronic isosporiasis. Strongyloidiasis is caused by a nematode worm, Strongyloides stercoralis. Administration of corticosteroids to patients with chronic low-grade S. stercoralis infection can trigger a fulminant, life-threatening form of strongyloidiasis.

Immunity to Cryptosporidium muris infection in mice is expressed through gut CD4+ intraepithelial lymphocytes

The role of gut intraepithelial lymphocytes (IEL) in immunity to cryptosporidial infection was investigated with a murine infection model involving Cryptosporidium muris. Oocyst shedding was monitored in severe combined immunodeficiency (SCID) mice infected with C. muris following intravenous injection of mesenteric lymph node (MLN) cells or intestinal IEL from BALB/c donor mice which were naive or previously infected with C. muris. SCID mice receiving no lymphoid cells developed chronic infections and excreted large numbers of oocysts until the end of the experiment. SCID mice injected with IEL from immune animals, however, were able to overcome the infection, and furthermore, these animals produced fewer oocysts and recovered sooner than ones which received IEL or MLN cells from naive BALB/c donors. Similar levels of protection were obtained in SCID mice injected with either 2 X 10(6) IEL or MLN cells from immune donor mice. Depletion of CD4+ cells from immune IEL, however, abrogated the ability to transfer immunity to SCID mice, while depletion of CD8+ cells only marginally reduced the protective capacity of immune IEL. Finally, control SCID mice which received no lymphocytes had < or = 1% CD4+ cells in the IEL from the small intestine, whereas the IEL from SCID mice recovered from infection, as a result of injection with immune IEL, contained 15% CD4+ cells. Thus, the ability to control C. muris infection correlated with the presence of the protective CD4+ cells in the gut epithelium.

Adoptive transfer of T lymphocytes to T-cell-depleted mice inhibits Escherichia coli translocation from the gastrointestinal tract

Bacterial translocation is defined as the passage of viable bacteria from the gastrointestinal (GI) tract to extraintestinal sites, such as the mesenteric lymph node (MLN), spleen, liver, kidneys, and blood. Previously, we reported that depletion of CD4+ and/or CD8+ T cells promotes bacterial translocation from the GI tract to the MLN. In the present study, CD4+ and/or CD8+ T cells, harvested from donor mice, were adoptively transferred to mice previously depleted of T cells by thymectomy plus intraperitoneal injection of rat anti-mouse T-cell monoclonal antibodies. The adoptively transferred CD4+ and/or CD8+ T cells inhibited the translocation of Escherichia coli from the GI tract. Migration of the adoptively transferred T cells to the spleens and MLNs of the recipient mice was determined by utilizing Thy 1.1+ donor cells adoptively transferred into mice whose cells express the Thy 1.2 marker. These results provide further evidence of the importance of T cells in the host immune defense against bacterial translocation from the GI tract.

Resolution of cryptosporidial infection in mice correlates with parasite-specific lymphocyte proliferation associated with both Th1 and Th2 cytokine secretion

This study was designed to investigate and characterize T-cell responses which lead to elimination of a primary infection of Cryptosporidium muris in BALB/c mice. The proliferative response of spleen cells to parasite antigen was measured by uptake of 3H-thymidine and, in parallel, supernatants were removed from cells to measure levels of IFN-gamma, TNF, IL-2 and IL-4 by ELISA. Oocyst excretion in faeces was first detected on day 10 post infection (p.i.); the level of shedding subsequently increased until day 14 and then declined until no oocysts were detected by day 25. The proliferative response of spleen cells from infected animals was similar to control levels up to day 14 p.i. but increased significantly on day 21 and was even greater on day 26. IFN-gamma and IL-2 were detected initially on day 14 p.i. and significantly higher concentrations were found on days 21 and 26. IL-4 secretion was also detected, but not until day 21 p.i., and production of TNF was not found at any time. Depletion of T-cells or CD4+ cells from spleen cells cultured with antigen resulted in a significant decrease in the levels of cytokine detected. These results indicated, therefore, that in BALB/c mice there was a correlation between the development of immunity to C. muris infection and both a parasite antigen-specific proliferative response and Th1 and Th2 cytokine production by spleen cells.

Mechanisms of innate and acquired resistance to Cryptosporidium parvum infection in SCID mice

SCID mice, which lack T and B cells, were used as hosts to investigate the nature of both T cell-independent and T-cell-dependent immune responses to infection with Cryptosporidium parvum. We found previously that SCID mice developed chronic infections in which the level of oocyst excretion was low up to about eight weeks post-infection but then increased significantly to cause morbidity and death after 13 weeks. In the present study, weekly administration of an anti-IFN-gamma monoclonal antibody (MoAb) resulted in a shortened prepatent time, significant increase in oocyst excretion and early onset of disease and death. These results suggested an immunologically mediated resistance to C. parvum in the SCID host which required the production of IFN-gamma. Attempts to demonstrate a role for TNF in nonspecific immunity were unsuccessful as injection of mice at weekly intervals with an anti-TNF MoAb failed to alter the course of infection. In contrast to the chronic infection observed in the mice above, SCID mice reconstituted with spleen cells from naive BALB/c mice were able to recover. Depletion of CD4+ cells from the donor population abrogated this protective effect. Mice receiving spleen cells depleted of CD8+ cells were able to recover but the patent infection was prolonged compared with those obtained in mice receiving unfractionated cells. These results demonstrate that CD4+ cells are necessary for the development of immunity to C. parvum infection in reconstituted SCID mice, but, in addition, that CD8+ cells also make a significant contribution to this immunity.