Pathogenic nematodes suppress humoral responses to third-party antigens in vivo by IL-10-mediated interference with Th cell function

One third of the human population is infected with helminth parasites. To promote their longevity and to limit pathology, helminths have developed several strategies to suppress the immune response of their host. As this immune suppression also acts on unrelated third-party Ags, a preexisting helminth infection may interfere with vaccination efficacy. In this study, we show that natural infection with Litomosoides sigmodontis suppressed the humoral response to thymus-dependent but not to thymus-independent model Ags in C57BL/6 mice. Thereby, we provide evidence that reduced humoral responses were mediated by interference with Th cell function rather than by direct suppression of B cells in L. sigmodontis-infected mice. We directly demonstrate suppression of Ag-specific proliferation in OVA-specific Th cells after adoptive transfer into L. sigmodontis-infected mice that led to equally reduced production of OVA-specific IgG. Transferred Th cells displayed increased frequencies of Foxp3(+) after in vivo stimulation within infected but not within naive mice. Helminth-mediated suppression was induced by established L. sigmodontis infections but was completely independent of the individual worm burden. Using DEREG mice, we rule out a central role for host-derived regulatory T cells in the suppression of transferred Th cell proliferation. In contrast, we show that L. sigmodontis-induced, host-derived IL-10 mediated Foxp3 induction in transferred Th cells and significantly contributed to the observed Th cell hypoproliferation within infected mice.     

Schistosoma mansoni polypeptides immunogenic in mice vaccinated with radiation-attenuated cercariae

We compared the humoral immune response of mice protected against Schistosoma mansoni by vaccination with radiation-attenuated cercariae to that of patently infected mice, and we identified antigens that elicit a greater, or unique, immune response in the vaccinated mice. These comparisons were based upon radioimmunoprecipitations and immunodepletion of [35S]methionine-labeled schistosomular and adult worm polypeptides, followed by one- and two-dimensional polyacrylamide gel analyses. The humoral responses of patently infected mice and of mice vaccinated once were remarkably similar and were directed against schistosome glycoproteins ranging in molecular size from greater than 300 to less than 10 kDa. Exposing mice to a second vaccination resulted in a marked change in the immune response, to one predominantly directed toward high molecular size glycoproteins. Sequential immunodepletion techniques identified five schistosomular and seven adult worm antigens that showed a greater or unique immunogenicity in vaccinated mice as compared with patently infected mice. These adult worm antigens were purified by preparative sequential immunoaffinity chromatography and used to prepare a polyclonal antiserum, anti-irradiated vaccine. This antiserum bound to the surface of live newly transformed and lung-stage schistosomula, as assessed by immunofluorescence assays, and was reactive with a number of 125I-labeled schistosomular surface polypeptides, including a doublet of 150 kDa that was also recognized by sera of vaccinated mice but not by sera of patently infected mice.     

Humoral factors and nonspecific immune suppression in Syrian hamsters infected with Leishmania donovani

Leishmania donovani produces progressive wasting and ultimately fatal visceral leishmaniasis in Syrian hamsters and provides an excellent model of progressive disease in humans. Experimentally infected hamsters were used to investigate the development of nonspecific immune suppression during visceral leishmaniasis and its association with humoral factors and wasting. At 2 wk all infected hamsters had developed antibody against a 59-kDa parasite antigen not recognized by sera of control hamsters. By 4 wk, strong antibody responses were noted against antigens of 26, 35, 46, 69, 107, and 120 kDa. No additional antigen was recognized at 6 or 8 wk or in hamsters treated with high doses of a pentavalent antimonial (stibogluconate sodium, 100 mg/kg/day for 5 days). Weight loss was first noted in infected hamsters at 8 wk. No difference in splenic lymphocyte proliferation in response to concanavalin A (Con A) was noted at 2 wk, but by 6 wk infected animals had only 20% of the Con A response of controls, and by 8 wk only 13%. Furthermore, incubation of splenic lymphocytes from uninfected control animals with 5% fetal calf serum and 5% serum from infected hamsters obtained at 4, 6, or 8 wk suppressed Con A responses by 50%, 99%, and 100%, respectively. Spleen cells from drug-treated animals exhibited no suppression of Con A responses when incubated with 5% autologous serum, but there was profound suppression when they were incubated with 5% autologous serum obtained during the acute phase of infection. Humoral factors, but not wasting, contributed to the suppression of lymphocyte responses.     

A comparative study of the death of schistosomula of Schistosoma haematobium and Schistosoma mansoni in the skin of mice and hamsters.

This study shows that some cercariae of S. haematobium and S. mansoni die during penetration of mouse or hamster skin. Approximately 30-38% of cercariae of both species die in mouse skin and 14-16% die in hamster skin. The greater number of cercariae which die in the skin of mice seems to account for the higher yield of adult worms recovered in hamsters. Adult worm recoveries from animals infected with S. haematobium were, however, only about half the worm recoveries from hosts infected with S. mansoni.     

Dirofilaria immitis: Parasite-specific humoral and cellular immune responses in experimentally infected dogs

Humoral and cellular immune responses to adult antigens of Dirofilaria immitis were evaluated in experimentally infected dogs during the chronic phase of infection. All infected dogs had significantly elevated IgG (enzyme-linked immunosorbent assay) and IgE (passive cutaneous anaphylaxis) titers against D. immitis adult antigens. However, there was little difference between infected dogs and uninfected controls in cellular-immune responses to D. immitis adult antigen or phytohemagglutinin as assessed by the lymphocyte transformation assay. Although neither cellular nor humoral responses correlated with worm burdens, cellular responses among infected dogs correlated inversely with IgG titers to D. immitis adult antigen. These results are consistent with observations in other nematode and trematode systems which suggest that in chronic tissue helminth infections there is suppression of cellular immune responses to parasite antigens while humoral responses to the same antigens remain relatively preserved.     

Effect ofDaucus carota var.boissieri extracts on immune response ofSchistosoma mansoni infected mice

Isolation and structure elucidation was carried out of flavonoid constituents found in fractionated extracts of the seeds and green leaves of Daucus carota L. var. boissieri (Apiaceae). The flavonoids are mainly apigenin, luteolin, their glycosidic precursors and 2,4,5-trimethoxybenzaldehyde. Fatty acids, hydrocarbons and sterols were identified by GLC. The effect of various carrot extracts on the immune responses of Schistosoma mansoni infected mice was studied. The rate of reduction in worm infestation in mice injected with some fractions indicated a strong protection. Some extracts induced humoral immune response through raising the IgG level at 2, 4 and 6 weeks post-infection as compared with infected control. The phenotypic analysis of the cellular immune response in spleen and mesenteric lymph nodes was accomplished by direct immunofluorescence. The data showed that some extracts stimulated the blastogenesis of CD4(+)-T splenocytes and mesenteric lymph node cells.     

Experimental infection of Nematospiroides dubius in Swiss albino mice. VII. Worm burdens and serum protein fractions

The paper deals with the alterations in serum protein profiles and its possible correlation with the worm burden in Swiss white mice infected with single and repeated doses of N. dubius infective larvae. Marked changes observed in serum protein fractions in all the groups were found to be further raised with increase in dose levels. However, maximum (optimal) changes of different fractions depend on the total number of larvae inoculated irrespective of the number of inoculations given. Percentage of worm retention was found to be inversely proportional to the number of larvae inoculated. Worm expulsion during repeated infections was attributed to the therefore, participation of increased amount of immunoglobulins and, humoral immunity (immediate type) has been suggested to play a major role in the immune mechanism of this model.     

Inhibition of the immune response by membrane-bound antibody.

Cells from the spleens of "normal" swine, which were pretreated with pronase to remove surface membrane-bound immunoglobulin, gave an enhanced hemolytic plaque-forming cell response to sheep red blood cells in vitro in comparison with untreated controls. The enhancement could be abrogated by preincubating pronase-treated spleeen cells in preparations containing antibody to sheep red blood cells. This effect was demonstrated by autologous sera, immune sera, and all three known classes of porcine serum immunoglobulins, including IgM, IgA, and IgG and could be removed by absorption with sheep red blood cells. Surface membrane-bound antibody exerted its effect by binding to the nonadherent cell population. The response of normal spleen cells was unaffected by antibody treatment. Pronase-treatment was not mitogenic, did not function as a polyclonal B cell activator, and did not selectively eliminate T or B cells. The results indicate that removal of antibody from the surface of lymphoid cells enhanced the humoral immune response invitro and confirm that membrane-bound antibody can inhibit response to antigen.     

Trichinella spiralis: dose dependence and kinetics of the mucosal immune response in mice.

The role of the mucosal immune response in helminth infections is not clear. In this study, the dose dependence and kinetics of the mucosal immune response to Trichinella spiralis were determined in experimentally infected Swiss Webster and BALB/c mice. The primary mucosal isotype was sIgA, although IgG was also detected, and primary infections with 10 and 150 larvae produced an anamnestic response on challenge. The mucosal and systemic immunoglobulin responses were dose dependent in both primary and challenge infections. The fecundity and length of worms and the rate of expulsion from the gut were determined on Day 6 postchallenge in Swiss Webster mice. Adult worm recovery and fecundity were reduced by greater than 50% and worm length by 28% in mice infected and challenged with 10 larvae and by 90, 85, and 35%, respectively, in mice infected and challenged with 150 larvae. The rate of expulsion was correlated with the size of both primary and challenge doses and a reduction in fecundity was correlated with the size of the primary dose only. The reduction in worm length did not differ significantly between the infection doses, but the trend was similar to that for expulsion. In BALB/c mice the expulsion response was dissociated from a reduction in fecundity and worm length, the latter two being positively correlated with sIgA levels, supporting a role for sIgA and/or IgG in these effects. However, expulsion does not appear to be dependent on the mucosal immunoglobulin response.     

The effect of platelet-activating factor and its antagonist--BN 52021--on immune reactions in vivo in mice and in vitro

The effect produced by the injection of platelet activation factor (PAF) and its antagonist BN 52021 on the intensity of humoral immune response in (CBA x C57BL)F1 mice was studied. PAF was found to stimulate the formation of antibodies to sheep red blood cells. In addition PAF stimulated the phagocytic activity of mouse peritoneal macrophages. The stimulation of immune response under the action of PAF may be attributed to an increase in the phagocytic activity of macrophages. The stimulating effect of PAF on immune response in vivo was abolished by the injection of BN 52021, the antagonist of PAF. At the same time the dose-dependent decrease of immune response was observed after the injection of BN 52021. Indomethacin, an inhibitor of prostaglandin synthesis, when administered to mice treated with BN 52021, abolished the BN 52021-induced suppression of humoral immune response. Mouse peritoneal macrophages, treated in vitro with BN 52021, were found to produce significantly more prostaglandin E than control macrophages. Thus, BN 52021 induced the suppression of humoral immune response in vivo; this suppression was probably due to the action of prostaglandin E2, a messenger of the second order. Besides, the PAF antagonist BN 52021 significantly decreased leukotriene B4 production by macrophages in vitro. BN 52021 may be supposed to switch over the synthesis and/or secretion of arachidonic acid from the lipoxygenase pathway to the cycloxygenase one.     

Humoral antibody response of the tilapia Oreochromis niloticus against Cichlidogyrus spp. (Monogenea)

The humoral immune response of the tilapia Oreochromis niloticus was evaluated using a direct ELISA. Serum was tested from fish infected with Cichlidogyrus spp. (Monogenea) and from fish injected intraperitoneally with the Cichlidogyrus spp. antigenic extract, i.e., 150 microl of the Cichlidogyrus spp. saline extract diluted in Freund's complete adjuvant (FCA) (1:1) were inoculated intraperitoneally at day 0, followed by 2 dosages of 50 microl of the same Cichlidogyrus spp. saline extract diluted in Freund's incomplete adjuvant (FIA) (1:1) at weeks 2 and 4, respectively. The humoral response was also evaluated by the double immunodiffusion test (DID) and by serum protein and total immunoglobulin (Ig) determinations. The IgM OD values in the hyperimmune fish were significantly higher than in the infected and uninfected fish groups. In the DID test, a precipitation (antigen-antibody) band was observed between the Cichlidogyrus spp. saline extract and hyperimmune sera, but not with the other groups. Increases in serum protein concentration and total Igs were observed in the immunized fish at weeks 2 and 10 postinjection. Results from this study suggest that tilapia is capable of producing an induced humoral immune response against an antigenic extract of Cichlidogyrus spp.     

Effect of Mycoplasma arthritidis on mouse and rat lymphoid cells in experimental Mycoplasma infection]

Early stages of mycoplasma infection of mice and rats were accompanied by suppression of the populations of rosette- and plaque-forming cells. Later the character and dynamics of the immune response to M. arthritidis differed in mice and rats. In mice mycoplasma infection was accompanied by stimulation of rosette-forming cells with some suppression of the plaque-forming cells from the 7th to the 36th day of infection. In rats by the 7th day the number of plaque- and rosette-forming cells decreased in comparison with control, and the immune response was restored by the 15h day; at later periods the immune response of the infected rats exceeded the normal level considerably. The cellular and humoral immune reactions proved to depend on the mycoplasma dose.     

Cyclophosphamide-induced specific suppression of the protective immune response to rodent malaria.

Nonspecific and specific chemosuppression of the immune response to Plasmodium berghei protective antigens were investigated. Specific immunosuppression was defined operationally as the selective suppression of the protective response to the parasite in mice injected with a combination of gamma-irradiated infected mouse erythrocytes (gammaPb) and cyclophosphamide (CY) with continued responsiveness to sheep erythrocytes (SRBC). After initial treatment (gammaPb + CY), mice were injected with gammaPb in potentially immunogenic doses. These and appropriate control animals were later challenged with nonirradiated infected mouse erythrocytes. The influence of the initial treatment regimens on the protective response was evaluated by parasitemia, and mortality was observed after challenge. Specificity of suppression was measured by evaluating the ability of mice to produce antibody to SRBC. Both specific and nonspecific suppression of the protective response to malaria were noted. Initial treatment with drug alone resulted in increased parasitemia and mortality and suppression of the SRBC antibody synthesis in drug-pretreated immunized mice as compared with immunized mice not pretreated with the drug. On the other hand, suppression of the response to the parasite, but not to SRBC, in animals pretreated with gammaPb + CY was clearly greater than that induced by drug alone. Thus, animals treated with malarial antigen and cyclophosphamide develop a measurable specific immunosuppression. These studies indicate that immunity to malaria is influenced by both cyclophosphamide alone (general immunosuppression) and cyclophosphamide in combination with antigen (specific immunosuppression) in a manner analogous to other immune responses.     

Serum protein changes in lead exposed mice infected with Hymenolepis nana

Significant decrease in serum globulin took place in Hymenolepis nana mouse model treated with lead prior to infection. Decrease of alpha, beta and gamma globulins was maximum on day 4 in comparison to that of control, gradually tapering off by day 100 when suppression was minimum with the experimental values almost reaching the same level as those of the control. Thus, suppression of globulins was neither total nor permanent.     

Virus-induced immunosuppression: immune system-mediated destruction of virus-infected dendritic cells results in generalized immune suppression.

Despite the clinical importance of virus-induced immunosuppression, how virus infection may lead to a generalized suppression of the host immune response is poorly understood. To elucidate the principles involved, we analyzed the mechanism by which a lymphocytic choriomeningitis virus (LCMV) variant produces a generalized immune suppression in its natural host, the mouse. Whereas adult mice inoculated intravenously with LCMV Armstrong rapidly clear the infection and remain immunocompetent, inoculation with the Armstrong-derived LCMV variant clone 13, which differs from its parent virus at only two amino acid positions, by contrast results in persistent infection and a generalized deficit in responsiveness to subsequent immune challenge. Here we show that the immune suppression induced by LCMV clone 13 is associated with a CD8-dependent loss of interdigitating dendritic cells from periarteriolar lymphoid sheaths in the spleen and, functionally, with a deficit in the ability of splenocytes from infected mice to stimulate the proliferation of naive T cells in a primary mixed lymphocyte reaction. Dendritic cells are not depleted in immunocompetent Armstrong-infected mice. LCMV Armstrong and clone 13 exhibit differences in their tropism within the spleen, with clone 13 causing a higher level of infection of antigen-presenting cells in the white pulp, including periarterial interdigitating dendritic cells, than Armstrong, thereby rendering these cells targets for destruction by the antiviral CD8+ cytotoxic T-lymphocyte response which is induced at early times following infection with either virus. Our findings illustrate the key role that virus tropism may play in determining pathogenicity and, further, document a mechanism for virus-induced immunosuppression which may contribute to the clinically important immune suppression associated with many virus infections, including human immunodeficiency virus type 1.     

Trichinella spiralis: antifecundity and antinewborn larvae immunity in swine

The development of antifecundity and antinewborn larvae immunity in swine infected with Trichinella spiralis was investigated. In primary infections, adult female worm fecundity dropped sharply after 3 weeks, although adults could be recovered from the small intestine for at least 7 weeks after infection. In challenge infections of pigs infected previously, adult female worm fecundity was depressed up to 51% and the adults were expelled within 3 weeks. Since immune pigs are almost completely resistant to the secondary establishment of muscle larvae, this suggested the existence of immune effector mechanisms also acting on the newborn larvae. This was supported by observations, using an indirect fluorescent antibody assay, that pig antibody bound to the surface of the newborn larvae. Passive transfer of immune pig serum resulted in a large reduction in muscle larvae burden in both infected pig and rat recipients. Adult female worm fecundity in such immune serum recipients was reduced only by 20% and worm survival in the intestine was unaffected. These results indicate that immunity to the newborn larvae, in addition to antifecundity effects, are responsible for the high levels of acquired resistance to T. spiralis in swine.     

Protein supply influences the nutritional penalty associated with the development of immunity in lambs infected with Trichostrongylus colubriformis

The influence of dietary protein supply on the nutritional penalty associated with the acquisition phase of the immune response to gastrointestinal nematodes in lambs was investigated. Groups of lambs were offered either a low-protein diet (L; 62 g metabolizable protein (MP)/kg dry matter (DM)) or high-protein diet (H; 95 g MP/kg DM) while being either infected with the equivalent of 2.000 L3 Trichostrongylus colubriformis/day (IF), similarly infected and concurrently immuno-suppressed with methylprednisolone acetate (ISIF), immuno-suppressed only (IS) or kept as uninfected controls (C). Body composition of all animals was measured on days -8 and 76 of infection using X-ray computed tomography. Temporal changes in serum phosphate and serum albumin concentrations, which provided an indicator of pathological damage, in addition to patterns of total daily nematode egg excretion and comparative worm burdens at slaughter indicated that a protective immune response was developed in H-IF, but not L-IF, H-ISIF or L-ISIF groups. Compared to their respective non-infected controls, the gross efficiency of use of metabolizable energy (ME) for net energy (NE) deposition in the carcass was reduced by 0.23 in H-IF (P < 0.05), 0.13 in H-ISIF (P > 0.05), 0.49 in L-IF (P < 0.01) and 0.23 in L-ISIF (P > 0.05). It is concluded that the reduction in ME utilization and reduced performance, which can be attributed to the immunological response, are lessened in animals offered a high-protein diet. Furthermore, evidence is presented to indicate a possible association between T. colubriformis L3 IgA antibody production and loss of performance in lambs infected with this nematode.     

Can Immune Response Mechanisms Explain the Fecal Shedding Patterns of Cattle Infected with Mycobacterium avium Subspecies paratuberculosis?

Johne’s disease (JD) is a chronic disease in ruminants and is caused by infection with Mycobacterium avium subspecies paratuberculosis (MAP). At late stages of the disease, MAP bacilli are shed via feces excretion and in turn create the potential for oral-fecal transmission. The role of the host immune response in MAP bacteria shedding patterns at different stages of JD is still unclear. We employed mathematical modeling to predict if the variation in MAP shedding could be correlated to the immune response in infected animals. We used a novel inverse modeling approach that assumed biological interactions among the antigen-specific lymphocyte proliferation response (cell-mediated response), antibody/humoral immune responses, and MAP bacteria. The modeling framework was used to predict and test possible biological interactions between the measured variables and returns only the essential interactions that are relevant in explaining the observed cattle MAP experimental infection data. Through confronting the models with data, we predicted observed effects (enhancement or suppression) and extents of interactions among the three variables. This analysis enabled classification of the infected cattle into three different groups that correspond to the unique predicted immune responses that are essential to explain the data from cattle within these groups. Our analysis highlights the strong and weak points of the modeling approach, as well as the key immune mechanisms predicted to be expressed in all animals and those that were different between animals, hence giving insight into how animals exhibit different disease dynamics and bacteria shedding patterns.     

Effects of cyclophosphamide on pigs infected and vaccinated with swinepox virus

Piglets treated with cyclophosphamide (50 mg/kg body wt, iv) before infection/vaccination with swinepox virus showed a strong suppression of humoral immune response. Cell mediated immune response was also affected to some extent and the cyclophosphamide treated piglets did not resist the challenge on 21 day post infection/vaccination and developed mild lesions.     

Increased susceptibility of lead exposed chickens to experimental infection of Ascaridia galli

Two sets of one day old, white leghorn (Victoria Strain) chickens were each orally exposed to 1.0 mg lead nitrate daily for 7 days and subsequently infected with 15 and 30 A. galli eggs. These experimental chickens exposed to lead harboured significantly greater worm burden when compared to unexposed controls leading strong support to the view that lead exposure significantly suppressed their immune response to A. galli infection. It also indicated that exposure of lead prior to infection greatly impaired weakened the immune capability of such chickens.