Role of host antibody in the chemotherapeutic action of praziquantel against Schistosoma mansoni: identification of target antigens.

We have demonstrated previously in a mouse model that effective chemotherapy against Schistosoma mansoni with praziquantel (PZQ) is dependent upon an intact host antibody response. In the same study, it was found that worms recovered from PZQ-treated animals display surface-bound antibodies. In order to identify the target antigens of the antibodies involved in the synergy between PZQ and the immune response, monoclonal antibodies (mAbs) and polyclonal antisera recognizing different tegumental components were tested by indirect immunofluorescence (IF) assay for their ability to bind in vitro to the surface of 6-week-old schistosomes perfused from nude (athymic) mice 1 h after PZQ treatment. Nude mice were used as hosts because worms from these animals were found to lack bound anti-schistosome antibodies. Only 5 of the 21 antibodies tested reacted with drug-treated worms. This indicated that the damage caused by PZQ to the schistosome tegument is restricted to specific tegumental components. Of the positive reactions, one group of antibodies gave IF patterns different from, whereas the other group gave IF reactions similar to those seen with worms perfused from immunologically intact mice. Antibodies against a schistosome esterase and alkaline phosphatase produced reaction patterns in the former category. In contrast, two out of three monoclonal antibodies recognizing different epitopes on a 200-kDa glycoprotein abundant in worm tubercles gave IF patterns very similar to those observed on schistosomes from drug-treated, intact mice. The biological significance of these reactions was confirmed by demonstrating that transfer of one of the positive monoclonal antibodies to 6-week-infected, B cell-depleted (mu-suppressed) mice reconstitutes the efficacy of PZQ treatment to normal levels. The above results suggest that the antibodies involved in the mechanism of action of PZQ react with a limited set of antigens. Furthermore, they implicate the 200-kDa tubercle protein as a major target of this response in naturally infected hosts.

Molecular identity of a major antigen of Schistosoma mansoni which cross-reacts with Trichinella spiralis and Fasciola hepatica.

A glycoprotein cross-reactive among Schistosoma mansoni, Trichinella spiralis and Fasciola hepatica was identified and characterized by use of monoclonal antibodies prepared against S. mansoni glycoproteins. Four monoclonal antibodies recognized the same antigen which was one of the major S. mansoni glycoproteins precipitated by sera of hosts infected with either S. mansoni or T. spiralis. This antigen was expressed in S. mansoni cercariae, adult male and female worms, and eggs, and in S. haematobium but not in S. japonicum. Radio-immunoprecipitation and partial proteolytic digest mapping showed that the monoclonal antibodies each recognized a unique epitope. These epitopes were heat labile, sensitive to chaotropic agents, but resistant to reduction and alkylation or digestion with glycosidases, indicating that the recognition sites were amino acids and not carbohydrates. Epitopes recognized by the four monoclonal antibodies were expressed in F. hepatica, whereas only two were expressed in T. spiralis. Analysis by immunofluorescence microscopy showed that the antigen was expressed in S. mansoni in the parenchymal tissue and on the surface of the dorsal tubercles; in mature F. hepatica in the parenchymal tissue, vitelline glands and eggs; in immature F. hepatica only in the parenchymal tissue and in larval T. spiralis in the hypodermis.

Identification of antigenic Schistosoma mansoni glycoproteins during the course of infection in mice and humans.

The progression of humoral immune responses exhibited by mice during the year following exposure to Schistosoma mansoni cercariae was established by studying radioimmunoprecipitations of adult male and cercarial glycoproteins. 35S-methionine metabolically-labeled adult S. mansoni male worm glycoproteins precipitated by sera of 14 mice were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The initial specific antibody response (week 5) was directed against 3 worm glycoproteins of 55,000, 52,000 and 35,000 molecular weight (Mr). As infection progressed, all major worm glycoproteins (ranging from 400,000 to 12,000 Mr) were precipitated by sera from each mouse and only minor individual variations in titer were noted in the antibody responses of the mice against these glycoproteins. Maximal immunoreactivity toward the radiolabeled glycoproteins occurred at week 20 and remained at this level through week 50. Analogous experiments with sera from acutely- and chronically-infected humans resulted in immunoprecipitation patterns almost identical to those obtained with sera from the corresponding experimentally-infected mice. The kinetics of the antibody response against 125Iodine-labeled cercarial glycoproteins was the same as that observed with worm glycoproteins.

Schistosoma mansoni, S. haematobium, and S. japonicum: identification of genus- and species-specific antigenic egg glycoproteins.

Immunoreactive egg glycoproteins of Schistosoma mansoni, S. haematobium, and S. japonicum which are genus- and species-specific, or react with sera of patients infected with other parasites, have been identified. Egg proteins were labeled with Iodine-125, and the concanavalin A-binding glycoproteins were immunoprecipitated with sera of patients infected with one of four species of Schistosoma or Trichinella spiralis, Taenia solium, Echinococcus granulosus, Entamoeba histolytica, or Wuchereria bancrofti. These immunoprecipitates were analyzed by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Despite the strikingly different patterns of glycoproteins of the African species, the antibody immune responses of patients infected with S. mansoni and S. haematobium were found to be so similar that differentiation could not be established. In contrast, sera of patients infected with S. japonicum, S. mekongi, or parasites not of the genus Schistosoma, immunoprecipitated fewer of the major S. mansoni or S. haematobium glycoproteins. Likewise, antibody immune responses of patients infected with the Oriental schistosomes (S. japonicum and S. mekongi) could not be differentiated. Only a few quantitative differences were noted between our S. mansoni egg glycoprotein extract and a standardized soluble egg antigen extract. This study provides an explanation for the extensive cross-reactivity observed in diagnostic assays which utilize various fractions of schistosomal egg extracts as the antigen.

Schistosoma mansoni, S. haematobium, and S. japonicum: identification of genus-, species-, and gender-specific antigenic worm glycoproteins.

Immunoreactive glycoproteins of Schistosoma mansoni, S. haematobium, and S. japonicum adult worms which are genus-, species-, and gender-specific, or react with sera of patients infected with other parasites, have been identified. Schistosomes were metabolically labeled with [35S]methionine and the concanavalin-A binding glycoproteins that were immunoprecipitated with sera of patients infected with one of three species of Schistosoma or Trichinella spiralis, Taenia solium, Echinococcus granulosus, Entamoeba histolytica, or Wuchereria bancrofti were analyzed by one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The S. mansoni glycoproteins that were immunoprecipitated by sera of patients infected with S. mansoni were indistinguishable from those precipitated by sera of patients infected with S. haematobium. Analogous results were obtained by use of S. haematobium glycoproteins as the radiolabeled antigen. In contrast, sera of patients infected with S. japonicum or parasites not of the genus Schistosoma immunoprecipitated fewer than half of the major S. mansoni or S. haematobium glycoproteins. Likewise, several S. japonicum glycoproteins were cross-reactive, while others exhibited genus, species, and gender specificity.

Tegumental expression in larval and adult stages of a major schistosome structural glycoprotein.

A monoclonal antibody has been used to identify and characterize an antigenic tegumental surface membrane glycoprotein of Schistosoma mansoni. Direct binding of 125I-labeled monoclonal antibody showed that this glycoprotein was present in eggs, cercariae, and worms of both sexes. The glycoprotein had an apparent molecular weight of 180,000. Indirect and direct immunofluorescent microscopy showed that this antigen was located on the interlinked tegumental folds of both larval and adult parasites. These findings are discussed in relation to parasite development and the mechanism by which schistosomes evade the host's immune defenses.