Taenia crassiceps: serum and surface immunoglobulins in metacestode infections of mice

Immunoregulation by Taenia crassiceps and its antigens

Taenia crassiceps is a cestode parasite of rodents (in its larval stage) and canids (in its adult stage) that can also parasitize immunocompromised humans. We have studied the immune response elicited by this helminth and its antigens in mice and human cells, and have discovered that they have a strong capacity to induce chronic Th2-type responses that are primarily characterized by high levels of Th2 cytokines, low proliferative responses in lymphocytes, an immature and LPS-tolerogenic profile in dendritic cells, the recruitment of myeloid-derived suppressor cells and, specially, alternatively activated macrophages. We also have utilized the immunoregulatory capabilities of this helminth to successfully modulate autoimmune responses and the outcome of other infectious diseases. In the present paper, we review the work of others and ourselves with regard to the immune response induced by T. crassiceps and its antigens, and we compare the advances in our understanding of this parasitic infection model with the knowledge that has been obtained from other selected models.

Ultrastructural studies on the cellular response of fish hosts following experimental infection with the plerocercoid of Ligula intestinalis (Cestoda: Pseudophyllidea)

With the exception of gudgeon (Gobio gobio) infection of cyprinid fish with the plerocercoid of Ligula intestinalis is associated with a host-tissue response. The nature and specificity of this response has been investigated using transplantation techniques. In roach there is an intense cellular response to implanted Sepharose, Spurr's resin and L. intestinalis, irrespective of donor host species. However, tegument damage only occurs in gudgeon-Ligula and cultured ro&ch-Ligula which has been exposed to gudgeon-plasma. L1 and L2 cell types predominate within the cellular response. Once the host leucocytes have breached the tegument, they migrate over the basal lamina and penetrate into the sub-tegumental region. In gudgeon an intense cellular attack occurs against Sepharose, Spurr's resin, ro&ch-Ligula and cultured gudgeon-Ligula which had been implanted directly or exposed to roach plasma. Tegument damage only occurs in the latter. In contrast, neither direct implantation of gudgeon-Ligula nor cultured roach-Ligula which has been exposed to gudgeon plasma evokes a cellular response. It is suggested that in these two instances, as in natural infections of gudgeon, protective host proteins may be absorbed onto the surface of the parasite.

Immunological responses in the mouse host to a cloned antigen of Taenia crassiceps

Adult female Swiss-Webster mice were immunized either intraperitoneally (IP) or subcutaneously (SQ) with cyst fluid or a genetically engineered fusion protein, Taenia crassiceps antigen 2-maltose binding protein (TCA2-MBP) from Taenia crassiceps metacestodes, or with live, non-budding cysts SQ, and then challenged IP with T. crassiceps metacestodes and necropsied 9 weeks later. Numbers of peripheral blood eosinophils were increased after IP immunization, but were not increased after SQ immunization or with SQ cysts given before the challenge infection. Eosinophil numbers gradually decreased over the course of the experiment, and were not found in increased numbers in the blood or peritoneal cavity at necropsy. Antigen-specific antibody responses were seen at day 14 or 28 in IP and SQ immunized groups: IgG1 and IgG3 isotypes continued to increase over the course of the experiment. A significant protective response was induced by immunization with the cyst fluid (15 +/- 4, X +/- SE recovered larvae) or the TCA2-MBP (22 +/- 12) given IP, but not SQ (122 +/- 36; 207 +/- 53, respectively) as measured by the numbers of larvae recovered at necropsy. Live cysts given SQ resulted in reduced numbers of cysts in the peritoneal cavity (188 +/- 66), but was not as effective as cyst fluid or TCA2-MBP given IP. Locally (IP) induced immune responses may be involved in the development of the protective response to a challenge infection with T. crassiceps metacestodes.

Molecular characterization of the surface and cyst fluid components of Taenia crassiceps

Information relating to the characterization of cestode surface macromolecules is limited. This is especially the case with Taenia crassiceps, a well-recognized model for the study of larval cestodiasis. Here, the protein and glycoprotein composition of the tegumental surface and cyst fluid of the metacestode have been investigated using radio-isotope labelling, immunoprecipitation, SDS-PAGE and lectin affinity chromatography. A restricted number of surface proteins was labelled with the 125I/Iodogen method although the majority were immunogenic; in contrast an array of cyst fluid antigens were labelled. Host serum proteins, including immunoglobulins, were identified on the surface and in the cyst fluid. Some of the 125I-labelled surface proteins, including a 37 kDa molecule, have been shown to be glycoproteins and probably contain-D-mannose and/or D-glucose; there is limited or no N-acetylglucosamine and no terminal galactose present on these components. A 37 kDa surface molecule, possibly the same glycoprotein, was also precipitated by infection sera and this may endorse the theory that highly immunogenic carbohydrates are continuously shed by T. crassiceps as a mechanism for diverting the immune response of the host. Radio-iodinated and biosynthetically labelled T. crassiceps antigens were highly cross-reactive with antibody raised to other cestodes and not one antigen was identified as a possible candidate for use in specific immunodiagnosis of any of the important taeniid infections.

Taenia crassiceps surface immunoglobulins: parasite- or host-derived?

In common with other taeniid cestodes, host or host-like proteins, especially immunoglobulins, occur on the surface and in the cyst fluid of Taenia crassiceps metacestodes. Here, several approaches have been used to determine the origin of the immunoglobulins present on the tegument. Indirect IFAT showed that IgG was almost totally lost from the surface of bladders after 6 days culture in vitro. There was a rapid reacquisition of immunoglobulins following incubation of the cultured metacestodes with either normal mouse serum or mouse anti-T. crassiceps antiserum. Immunoprecipitation of in vitro translation products and biosynthetically labelled T. crassiceps proteins with a panel of anti-IgG antisera failed to positively identify any molecule with homology to mammalian immunoglobulins. These results suggest strongly that the immunoglobulins located on the surface of T. crassiceps are of host rather than parasite origin. The occurrence of a relatively low abundance receptor in the surface of the bladders, which binds non-specific host immunoglobulin, together with surface-bound specific anti-T. crassiceps antibodies can account for the presence of these host proteins. Freshly obtained bladders and metacestodes cultured in vitro for 6 days were transplanted into naive mice and the survival and development of the resulting parasites compared. In some individual mice there was a decrease in the number and volume of metacestodes and an increase in encapsulated parasites arising from cultured bladders. This was probably not related to the loss of host immunoglobulins from the parasite surface during culture as the reacquisition of these proteins after transplantation is likely to be far more rapid than any immune response could evoke in a naive host.

Immunoelectrophoretic analyses of antigens shared by the vesicular fluid and cyst wall of Taenia crassiceps and Taenia saginata metacestodes

In this study, the antigenic mosaic of the vesicular fluid (VF) and hydrosoluble cyst-wall extract (CWE) of T. crassiceps (Tc; harvested from mice) and T. saginata (Ts) metacestodes was analyzed by combined precipitation maps developed in single and bidimensional immunoelectrophoresis against the respective rabbit antiserum. Host-serum proteins demonstrated by immunodiffusion within TcVF (albumin, transferrin, IgG, and another five noncharacterized proteins), TcCWE (albumin, IgG, and six additional unknown proteins), TsVF (albumin) and TsCWE (albumin and IgG) were removed by immunoaffinity chromatography prior to immunoelectrophoretic analysis. Neither TcVF nor TcCWE contained demonstrable amounts of mouse IgM and IgA. In TcVF a total of 18 and in TcCWE a total of 36 parasitic antigens were recognized by the corresponding antiserum. In the case of TsVF and TsCWE, antiserum to the crude extract of T. saginata larvae developed a total of 26 and 30 precipitates, respectively. Examination of the precipitation maps developed by the respective heterologous antiserum (vice-versa testing) showed that both TcVF and TsVF contained ten antigens sharing identity. For TcCWE and TsCWE, nearly the same number of shared antigens (20 and 18, respectively) could be demonstrated. For screening of IgG antibodies against T. saginata metacestodes from heavily and moderately infected calves (n = 6) by ELISA, VF and CWE antigens of both Taenia species were found to be potent reagents; TsVF was the most sensitive antigen.

Echinococcus multilocularis: the non-specific binding of different species of immunoglobulins to alveolar hydatid cysts grown in vivo and in vitro

Alveolar hydatid cysts (AHC) were isolated from C57BL/6J and BALB/c mice at 8 and 12 weeks post-infection from subcutaneous and intraperitoneal foci and cultured in vitro. Freshly isolated as well as in vitro-grown cysts were incubated with Fc or F(ab')2 fragments of human, rabbit, mouse, goat or sheep immunoglobulins, then washed and incubated with a fluorescein-conjugated rabbit or goat F(ab')2 fraction of antisera to each of the above primary sera. Significant fluorescence on the surface of AHC was detected when they were incubated with human, rabbit or mouse Fc fractions followed by the addition of goat or rabbit fluorescein-conjugated antiserum. No fluorescence was detected when the AHC were incubated with the F(ab')2 fragments and fluorescein-conjugated antiserum, except when the primary antiserum was mouse F(ab')2 fractions. Cysts grown in vitro retained their binding ability to human, rabbit or mouse Fc fractions. However, the intensity of fluorescence decreased proportionally with time. The maximum intensity of staining was observed with small cysts. Large cysts showed diminished fluorescence. The non-specific binding of human, mouse or rabbit immunoglobulins (Fc fractions) to AHC was also confirmed by rosetting with sheep erythrocytes (SRBC) which suggests that the larvae of Echinococcus multilocularis may utilize the presence of Fc receptors on their surface in order to elude immune destruction by the host.