The identification and characterization of new immunogenic egg components: implications for evaluation and control of the immunopathogenic T cell response in schistosomiasis

In schistosomiasis, granuloma formation to parasite eggs signals the beginning of a chronic and potentially life-threatening disease. Granulomas are strictly mediated by CD4+ T helper (Th) cells specific for egg antigens; however, the number and identity of these T cell-sensitizing molecules are largely unknown. We have used monoclonal T cell reagents derived from egg-sensitized individuals as probes to track down, isolate and positively identify several egg antigens; this approach implicitly assures that the molecules of interest are T cell immunogens and, hence, potentially pathogenic. The best studied and most abundant egg component is the Sm-p40 antigen. Sm-p40 and its peptide 234-246 elicit a strikingly immunodominant Th-1-polarized response in C3H and CBA mice, which are H-2k strains characterized by severe egg-induced immunopathology. Two additional recently described T cell-sensitizing egg antigens are Schistosoma mansoni phosphoenolpyruvate carboxykinase (Sm-PEPCK) and thioredoxin peroxidase-1 (Sm-TPx-1). In contrast to Sm-p40, both of these molecules induce a more balanced Th-1/Th-2 response, and are relatively stronger antigens in C57BL/6 mice, which develop smaller egg granulomas. Importantly, Sm-p40 and Sm-PEPCK have demonstrated immunogenicity in humans. The findings in the murine model introduce the important notion that egg antigens can vary significantly in immunogenicity according to the host's genetic background. A better knowledge of the principal immunogenic egg components is necessary to determine whether the immune responses to certain antigens can serve as indicators or predictors of the form and severity of clinical disease, and to ascertain whether such responses can be manipulated for the purpose of reducing pathology.

Th1-polarizing immunization with egg antigens correlates with severe exacerbation of immunopathology and death in schistosome infection

In schistosomiasis mansoni, parasite eggs precipitate an intrahepatic granulomatous and fibrosing inflammatory process, which is mediated by, and dependent on, MHC class II-restricted CD4 T helper (Th) lymphocytes specific for schistosome egg antigens (SEA). In the mouse model of the disease, CBA mice develop large granulomas, whereas in C57BL/6 (BL/6) mice these granulomas are significantly smaller. To further investigate how the prevailing cytokine environment influences the development of the egg-induced immunopathology, we immunized the low-pathology BL/6 mice with SEA in complete Freund's adjuvant (CFA) once before, and once again during, the course of a 7-week infection. This immunization caused a pronounced Th1 shift in the SEA-specific CD4 T cell response, which was detected in the mesenteric lymph nodes (MLNs) and spleens, as well as in the granulomatous lesions themselves. The immunized mice displayed a dramatic enhancement of hepatic egg-induced immunopathology manifested by a marked increase in granuloma size and parenchymal inflammation, leading to early death. Control mice immunized with equivalent amounts of SEA or CFA alone displayed the smaller hepatic lesions in a Th2-dominant environment typically seen in the unimmunized BL/6 mice. Analysis of granuloma and MLN lymphocytes from the SEA/CFA-immunized mice revealed that the proportion of CD4 T cells was unchanged in comparison with the control BL/6 groups and remained significantly lower than that seen in the normally high-pathology CBA strain. These results suggest that the shift toward Th1-type cytokine production by a numerically stable population of CD4 T cells correlates with severe exacerbation of immunopathology in schistosomiasis.

Nasal administration of Schistosoma mansoni egg antigen-cholera B subunit conjugate suppresses hepatic granuloma formation and reduces mortality in S. mansoni-infected mice

Granulomatous inflammation in schistosomiasis is a delayed-type hypersensitivity reaction mediated by CD4+ T cells specific for parasite egg antigens (Ags). In an attempt to control T-cell responses leading to excessive harmful inflammation and granuloma formation, especially in the liver, BALB/c mice were intranasally (i.n.) treated with soluble Schistosoma mansoni egg Ags (SEA) conjugated to cholera toxin B subunit (CTB), a mucosa-binding protein with demonstrated capacity to suppress inflammatory T-cell functions after mucosal administration. Treatment with CTB-SEA significantly conjugate a reduced liver granuloma formation in infected mice associated with decreased SEA specific Th1- and Th2-type immune responses by liver leukocytes. Importantly, treatment with CTB-SEA conjugate also significantly reduced the mortality in chronically infected mice. In S. mansoni-infected large-granuloma forming CBA mice, i.n. treatment with purified Sm-p40, the major egg antigen, conjugated to CTB likewise significantly inhibited hepatic egg granuloma formation. A reduction of SEA-driven lymphoproliferation and of interferon (IFN)-gamma, interleukin (IL)-4 and IL-5 production, together with an increase in transforming growth factor (TGF)-beta1 production, were observed in splenic cells from CTB-Sm-p40-treated SEA-sensitized mice, as well as in liver leukocytes from CTB-Sm-p40-treated schistosome-infected mice. These results indicate that mucosal administration of SEA or purified Sm-p40 antigen in conjunction with CTB is highly effective in curtailing immunopathologic manifestations of schistosomiasis in vivo in infected hosts.

Elucidation and role of critical residues of immunodominant peptide associated with T cell-mediated parasitic disease

Granulomatous inflammation in schistosomiasis is strictly dependent on CD4+ Th lymphocytes sensitized to egg Ags, but its intensity is genetically regulated. C3H and CBA (H-2k) are strains of mice that develop large granulomas; they also strongly respond to the major egg Ag Sm-p40. We now show that the immunodominant epitope recognized by CD4+ Th cells from infected H-2k mice is confined to 13-mer peptide 234-246 (PKSDNQIKAVPAS), which elicits an I-Ak-restricted Th1-type response. Using a panel of alanine-monosubstituted peptides, we identified Asp237 as the main contact residue with I-Ak. On the other hand, three TCR contact residues were essential to stimulate epitope-specific T cell hybridomas: for two hybridomas these were Asn238, Gln239, and Lys241; and for one, Asn238, Lys241, and Pro244. In one instance, alanine substitution for Gln239 generated an antagonist that blocked subsequent stimulation with wild-type peptide. Most importantly, replacement of Asn238, Gln239, or Lys241 caused a profound loss of polyclonal CD4+ T cell reactivity from schistosome-infected mice. This study identifies the critical residues of immunodominant peptide 234-246 involved in the T cell response against the Sm-p40 egg Ag and suggests that suitable altered peptides may be capable of precipitating its down-regulation.

A novel 62-kilodalton egg antigen from Schistosoma mansoni induces a potent CD4(+) T helper cell response in the C57BL/6 mouse

In infection with Schistosoma mansoni, hepatic granuloma formation is mediated by CD4(+) T helper (Th) cells sensitized to schistosomal egg antigens. There is considerable variation among infected individuals with respect to both severity of disease and the T-cell response to egg antigens. In the BL/6 mouse, the egg granulomas are relatively small and the relevant sensitizing egg antigens are largely unknown. We investigated the CD4(+) Th cell response of infected BL/6 mice to egg antigens fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and found a prominent lymphoproliferative response to be directed against a 62-kDa component. With the aid of a specific T-cell hybridoma, 4E6, the 62-kDa antigen was isolated; following partial digestion with endoproteinase Glu-C, an internal amino acid sequence was found to be identical with one present in the enzyme phosphoenolpyruvate carboxykinase (PEPCK) of the organisms Caenorhabditis elegans and Treponema pallidum and to differ by one residue from PEPCK of various other species. In CD4(+) Th cells from 7.5- 8.5-week-infected BL/6 mice, the purified 62-kDa molecule elicited a potent proliferative response which, based on cytokine analysis, was of a mixed Th-1 and Th-2 type. Our results reveal a novel egg antigen of particular prominence in the BL/6 mouse and suggest that the immune response in schistosomiasis is a product of sensitization to egg antigens that may vary considerably in immunogenicity from strain to strain.

Experimental murine schistosomiasis in the absence of B7 costimulatory molecules: reversal of elicited T cell cytokine profile and partial inhibition of egg granuloma formation

The granulomatous inflammation in infection with the helminth Schistosoma mansoni represents a cellular hypersensitivity reaction mediated by, and dependent upon, MHC class II-restricted CD4+ Th cells sensitized to parasite egg Ags. The current work examines the role and significance of the B7:CD28/CTLA-4 pathway in providing the costimulation necessary for the activation of these pathogenic T cells. In vitro T cell responses in B7-1-/- mice, 7-8 wk postinfection, were no different from wild-type controls, but the absence of B7-2 molecules resulted in a decrease in egg Ag-induced proliferation with increased IFN-gamma production. Both B7-1-/- and B7-2-/- mice exhibited intact granuloma formation. In contrast, CD4+ Th cells from B7-1/2 double-deficient mice displayed a dramatic loss of proliferative capacity upon stimulation with egg Ag. Most strikingly, these T cells secreted only IFN-gamma, but not IL-4 and IL-10, a pattern entirely opposite to that displayed by wild-type controls. Despite these major differences in T cell reactivity, B7-1/2-/- mice had only a limited reduction of granuloma size and fibrosis, without appreciable difference in cellular composition. These results show that substantial granuloma formation can occur under conditions of limited T cell expansion and restricted Th1-type cytokine production. They also support the notion that the combined effect of B7 signaling is not as critical for Th1 cell activation as it is for the development of the Th2 dominant environment characteristic of the evolving schistosome infection in H-2b mice.

Schistosoma mansoni: genetic restriction and cytokine profile of the CD4 + T helper cell response to dominant epitope peptide of major egg antigen Sm-p40

Granuloma formation in schistosomiasis is mediated by MHC class II-restricted CD4 + T helper lymphocytes sensitized to egg antigens. We previously reported that C3H mice, which develop large granulomas, display strong CD4 + T helper cell responses to the major egg antigen Sm-p40. Moreover, all members of a panel of egg antigen-specific T cell hybridomas responded to the Sm-p40 antigen. Given the significance of the Sm-p40 molecule in the C3H T cell repertoire against schistosomal egg antigens, the current work was undertaken to map its immunogenic epitopes, using a library of 15 synthetic overlapping 30-mer peptides. The dominant epitope recognized by polyclonal CD4 + Th cells was located in peptide 10 (amino acids 229-258); subdominant epitopes were detected in peptides 8 (amino acids 179-208) and 12 (amino acids 279-308). The anti-Sm-p40 T cell hybridomas variously responded to any one of the same three stimulatory peptides. Furthermore, studies with various mouse strains demonstrated that a strong anti-Sm-p40 response was restricted by H-2(k). Interestingly, the cells responding to peptide 10 and to the Sm-p40 antigen only secreted IL-2 and IFN-gamma, but not IL-4 and IL-10, indicating that they are entirely of the Th-1-type, a subset with demonstrated capacity to mediate egg granuloma formation. The identification of dominant epitopes within key egg antigens offers opportunities for desensitization of the CD4 + Th cells that mediate pathology in schistosomia sis.

The immune response and immunopathology in infection with Schistosoma mansoni: a key role of major egg antigen Sm-p40

The immune response and related granulomatous inflammation in infection with Schistosoma mansoni are ultimately dependent on SEA-sensitized CD4+ Th cells and comprise multiple pathways variously involving the activation and recruitment of different cell populations and the production of different inflammatory cytokines, all under the influence of regulatory genetic factors. The spontaneous downregulation of granuloma formation (immunomodulation), in turn, is a well-known phenomenon, but the full extent of its precipitating factors is still uncertain. This review describes a pathway leading to immunomodulation that features at its centre the down-regulatory cytokine IL-10. This mechanism is attractive because it offers a cogent correlation between findings in the laboratory and those displayed by patients affected with the disease. The Sm-p40 antigen, a major component of schistosome eggs, elicits a strong CD4+ Th cell response in H-2k mice that correlates with intense granuloma formation; in contrast, its immunogenicity is relatively minor during infection of other mouse strains that develop smaller granulomas. Of great interest is that the Sm-p40 antigen only elicits a Th-1 type cytokine response, a phenotype that remains constant even as the overall response to SEA shifts to a Th-2 type. The Sm-p40 molecule has a dominant epitope that is the target of CD4+ Th cells from infected H-2k mice; indeed, a minimal peptide that bears the epitope binds to I-Ak. The importance of pursuing a systematic elucidation of the major egg antigens, resides in the exciting possibility of specifically desensitizing the CD4+ Th cells that mediate granuloma formation, which may achieve meaningful prevention or amelioration of clinical disease.

In infection with Schistosoma mansoni, B cells are required for T helper type 2 cell responses but not for granuloma formation

The immune response and immunopathologic manifestations in schistosomiasis are largely dependent on Ag-specific CD4+ Th cells. In turn, the stimulatory/regulatory function of the Th cells is dependent on signals emanating from accessory cells. B cells are capable of functioning as accessory cells, and their role in experimental murine schistosomiasis was investigated by using mice with targeted mutations in the J(H) locus. This phenotype results in the absence of B cells and of Ab production. After 7.5- to 8-wk infections, mesenteric lymph node cells from the JHD B-less mice displayed lower proliferative responses to schistosomal egg Ag than did cells from infected control mice. Most importantly, compared with cells from controls, egg Ag-stimulated JHD lymph node cells produced significantly higher amounts of the Th1 response-associated cytokines IFN-gamma and IL-12, while their production of the Th2-type cytokines IL-4 and IL-10 was dramatically reduced or undetectable. Similarly, irradiated splenocytes from uninfected JHD mice, used as APC, elicited significantly stronger Th1 and weaker Th2 responses from egg Ag-specific CD4+ Th cells than splenocytes from control mice. Despite these sharply contrasting cytokine profiles, there were no significant differences either in the size and composition of the resulting egg granulomas or in the number of deposited eggs in the livers of infected JHD vs control mice. Taken together, the findings in the JHD mouse reflect an impairment in the ability to mount a Th2 response, which translates into a loss of the Th1 to Th2 switch characteristically seen in normal schistosome-infected mice. These results suggest that B cells promote Th2-type responses, and that typical granulomatous responses proceed in their absence.

In infection with Schistosoma mansoni, B cells are required for T helper type 2 cell responses but not for granuloma formation

The immune response and immunopathologic manifestations in schistosomiasis are largely dependent on Ag-specific CD4+ Th cells. In turn, the stimulatory/regulatory function of the Th cells is dependent on signals emanating from accessory cells. B cells are capable of functioning as accessory cells, and their role in experimental murine schistosomiasis was investigated by using mice with targeted mutations in the J(H) locus. This phenotype results in the absence of B cells and of Ab production. After 7.5- to 8-wk infections, mesenteric lymph node cells from the JHD B-less mice displayed lower proliferative responses to schistosomal egg Ag than did cells from infected control mice. Most importantly, compared with cells from controls, egg Ag-stimulated JHD lymph node cells produced significantly higher amounts of the Th1 response-associated cytokines IFN-gamma and IL-12, while their production of the Th2-type cytokines IL-4 and IL-10 was dramatically reduced or undetectable. Similarly, irradiated splenocytes from uninfected JHD mice, used as APC, elicited significantly stronger Th1 and weaker Th2 responses from egg Ag-specific CD4+ Th cells than splenocytes from control mice. Despite these sharply contrasting cytokine profiles, there were no significant differences either in the size and composition of the resulting egg granulomas or in the number of deposited eggs in the livers of infected JHD vs control mice. Taken together, the findings in the JHD mouse reflect an impairment in the ability to mount a Th2 response, which translates into a loss of the Th1 to Th2 switch characteristically seen in normal schistosome-infected mice. These results suggest that B cells promote Th2-type responses, and that typical granulomatous responses proceed in their absence.

Expression of class II, but not class I, major histocompatibility complex molecules is required for granuloma formation in infection with Schistosoma mansoni

Previous studies have suggested that granulomatous inflammation in schistosomiasis is mediated by CD4+ T helper lymphocytes sensitized to parasite egg antigens. However, CD8+ T cells have also frequently been associated with the immune response to schistosome eggs. To examine more precisely the role of CD4+ and CD8+ T cells in the pathology of the schistosomal infection, we used mice with targeted mutations in major histocompatibility complex (MHC) class II or class I molecules. These mutations lead, respectively, to the virtual absence of CD4+ and CD8+ T cells. The results clearly show that schistosome-infected MHC class II mutant mice failed to form granulomas around parasite eggs. In contrast, infected MHC class I mutant mice displayed characteristic granulomatous lesions that were comparable to those in wild-type control mice. Moreover, lymphoid cells from MHC class II mutant mice were unable to react to egg antigens with either proliferative or cytokine [interferon-gamma, interleukin (IL)-4, IL-10] responses; nor were they able to present egg antigens to specifically sensitized CD4+ T helper cells from infected syngeneic control mice. By comparison, cells from MHC class I mutant mice exercised all these functions in a manner comparable with those from wild-type controls. These observations clearly demonstrate that schistosomal egg granulomas are mediated by MHC class II-restricted CD4+ T helper cells. They also suggest that CD8+ T cells do not become sensitized to egg antigens and play little role, if any, in the pathogenesis of schistosomiasis.

Differential antigen recognition by T cell populations from strains of mice developing polar forms of granulomatous inflammation in response to eggs of Schistosoma mansoni

In humans, infection with schistosome helminths can lead to dissimilar forms of clinical disease. Likewise, in the experimental mouse system, identical infection protocols with Schistosoma mansoni cause a more severe granulomatous disease in the C3H strain than in the C57BL/6 strain. To address this difference, we developed panels of schistosomal egg antigen (SEA)-specific T cell hybridomas to compare the responses of C3H and C57BL/6 mice to the major egg antigen p40. All derived C3H T cell hybridomas, despite being clonally distinct and restricted by either I-Ak or I-Ek, responded to recombinant fragment 15-1 of the p40 antigen, while none of the C57BL/6 T cell hybridomas did. Consistent with the observed monoclonal T cell responses, polyclonal lymph node cells from schistosome-infected C3H mice reacted strongly to fragment 15-1, which contrasted sharply with the weak response displayed by the C57BL/6 strain. Moreover, studies with congenic mice demonstrated that the strong CD4+ T cell response to fragment 15-1 was under major histocompatibility complex control and segregated with the H-2k haplotype. These findings suggest that a dominant T cell response against a major egg antigen may represent a risk factor for the development of severe disease.

Quantitation of soluble E-receptor of T lymphocytes in serum from HIV-1 positive patients

Human T lymphocytes carry a membrane receptor for sheep erythrocytes (E) related to the CD2 molecule. The E-receptor is found in a soluble from (Rs) in serum and can be quantitated by "rocket electrophoresis" using an anti-Rs serum obtained by immunizing sheep with autologous erythrocytes coated with Rs. Increased serum levels of Rs are found in patients with diseases associated with immunodepression. In the present study, 14 asymptomatic HIV-1 seropositive individuals were investigated regarding their Rs levels and delayed hypersensitivity skin tests every 3 months for a period of 35 months. All these patients progressed to AIDS in this period. Rs serum levels have also been quantitated in 14 normal individuals. The mean Rs values in normal individuals, asymptomatic, and AIDS patients were, respectively: 4.8 +/- 1.5 mm (SD), 9.6 +/- 1.9 mm (SD) and 11.3 +/- 2.4 mm (SD). An increase of Rs serum levels was observed when we compared normal individuals with CDC-II and CDC-IV clinical stage patients (P < 0.05, Mann-Whitney test) and CDC-II and CDC-IV patients, (P < 0.05, Wilcoxon test). We have observed a depressed delayed hypersensitivity response to ubiquitous antigens in CDC-IV patients. Our results indicate that Rs serum levels can be used as a progression marker in HIV infected patients.

Delayed hypersensitivity skin tests in prognosis of human immunodeficiency virus infection

Delayed hypersensitivity skin tests (DHST) with recall antigens were investigated as prognostic markers in five different approaches. In the first study, 42 acquired immunodeficiency syndrome (AIDS) patients (IVb, IVcl, IVd, and IVe; MMWR 35:334-339, 1986) 26 AIDS-related complex (ARC) patients (IVa and IVc2), and 98 asymptomatic patients (II and III) were evaluated with candidin, tricophytin, PPD and streptokinase-streptodornase. In the second study, 10 patients (II and III) were evaluated sequentially with the same antigens. In the third, 45 patients with at least two positive skin tests ("reactors") were followed for one year and evaluated every 6 months with the same antigens. In the fourth, 16 "reactors" were followed and evaluated every 3 months with the same antigens. We measured the interval from the time at which patients first presented with only one or no positive DHST until the development of ARC or AIDS. In the last study, the correlation between absolute number of CD4+ lymphocytes and the number of DHST was studied in 151 patients. We found that the decrease in reactiveness to DHST correlated directly with the progression to AIDS, demonstrating the usefulness of this simple procedure as a valid prognostic marker.

Effect of large doses of the oral contraceptive Enovid on cholesterol metabolism in the rat

Short-term effects of the oral contraceptive drug, Enovid, a mixture of estrogenic and progesterone compounds, have been determined in experiments on male and female rats. Oral administration of large doses for 7 days resulted in marked decreases of cholesteryl esters in plasma accompanied by only slight elevations of hepatic cholesterol content. Cholesteryl esters were also much lower in adrenals and ovaries, organs which are usually responsible for steroid hormone biosynthesis. At the same time, cholesterol-esterifying activity in plasma was substantially increased. Enovid administration was shown also to affect the fatty acid composition of sterol esters remaining in plasma, adrenals, and ovaries. The concentration of linoleate and arachidonate was significantly decreased in plasma sterol esters, whereas the concentrations of arachidonate and docosatetraenoate in adrenals and of docosatetraenoate in ovaries were significantly lowered. All of the changes reported were more pronounced in the female than in the male rat. It is hypothesized that the decreased levels of cholesteryl ester found in the organs investigated, together with the increase in plasma cholesterol-esterifying activity, are probably associated either with changes in cholesterol biosynthesis and(or) transport or with an increase in cholesterol transformation to other steroids and excretion. These possibilities are now under investigation.