Entamoeba histolytica: cDNAs cloned as 30kDa collagen-binding proteins (CBP) belong to an antioxidant molecule family. Protection of hamsters from amoebic liver abscess by immunization with recombinant CBP

A cDNA expression library of Entamoeba histolytica was screened with antiserum to native amoebic collagen binding proteins (CBPs), and two clones C13 and C7 which partially encode for the 30 kDa CBP were obtained. The sequenced clones were 90% homologous. C7 had a 69 bp deletion at the 5' end that is present in C13 and encodes for a Glu-Cys-Lys rich region and a four amino acids repeat (Glu-Lys-Glu-Cys). Purified fusion proteins from these cDNA clones were able to bind native type I collagen gels in a pH, calcium, ionic strength, and temperature dependent way. The binding of pgtC13 to collagen gel was time and temperature stable, while pgtC7 binding was not, suggesting that the deleted region in C7 is important for the binding. The clones reported here partially encode a 30 kDa CBP that also belong to an antioxidant molecule family. We demonstrated that the fusion protein pgtC13 is immunogenic and partially protective as a subunit vaccine in the hamster model of amoebic liver abscess.

Biochemical and immunological characterization of soluble antigens of Giardia lamblia

The crude soluble antigens (CSA) of Giardia lamblia trophozoites and their analytically purified fractions were characterized biochemically and immunologically to determine the most immunogenic fraction and its localization on the parasite. Both Sephacryl S-300 column chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed the highly complex and heterogeneous nature of CSA. Gel filtration of CSA showed four fractions (FI-FIV) with molecular masses of 250, 150, 110, and 10 kDa for fractions I-IV, respectively. Protein profiles of CSA demonstrated 28 Coomassie-blue bands in the range of 200-14 kDa. Similar banding patterns with fewer polypeptides were observed in the FI fraction. However, fractions II and III showed polypeptide bands in the region of 97-14 kDa. The glycoprotein nature of CSA and its-fractions were demonstrated in physicochemical analysis. In antigenic activity analysis the high-molecular-weight FI antigen was found to be 8 times more immunogenic than CSA as well as the other fractions. Major differences in the immunoreactivity of CSA and FI antigens were noted at 220, 30, and 22 kDa for the FI antigen and at 205, 84, 55, 43, and 20 kDa for CSA. Some of these FI polypeptides were found to be surface-associated as revealed by immunofluorescence and immunoblot assay. These results suggest the future use of the FI antigen in the serodiagnosis of and immunoprophylaxis against giardiasis.

Production and characterization of monoclonal antibodies against a highly immunogenic fraction of Entamoeba histolytica (NIH:200) and their application in the detection of current amoebic infection

Six monoclonal antibodies (MAbs) were produced against a highly immunogenic fraction derived by the chromatographic separation of the soluble preparation of axenic Entamoeba histolytica (strain NIH:200) trophozoites. Isotype characterization of the six MAbs revealed that four belonged to the IgM class and one each to the IgG1 and the IgG2a subclasses. The immunoreactivity patterns and the specificity of the MAbs with homologous and heterologous antigens were analyzed by the enzyme-linked immunotransfer blot technique and by the enzyme-linked immunosorbent assay. The MAbs reacted intensely with isolates of E. histolytica (strain NIH:200 as well as a local isolate MX1) but showed no reactivity with Entamoeba coli, Iodamoeba butschlii, Endolimax nana, Entamoeba hartmanni, free-living amoeba (Acanthamoeba harticolus) and other enteric parasites. Using the IgG1 MAb as a detecting antibody, a polyclonal-monoclonal antibody-based enzyme-linked immunosorbent assay was developed for the detection of E. histolytica antigens in stool samples of infected patients. The detection limit of the assay was 8 ng of amoebic antigen. This test was found to be specific and sensitive and yielded 100% positive results in cases with amoebiasis but did not react with controls included in the evaluation. The MAb-based enzyme-linked immunosorbent assay developed in this study will be an important test for the diagnosis of E. histolytica in the feces of infected humans; however, the limitation of the test is the inability to discriminate the pathogenic status of the amoeba detected in the stool.

Detection of specific anti-Giardia antibodies in the serodiagnosis of symptomatic giardiasis

The roles of circulating anti-Giardia IgM and IgG antibodies were assayed by the Enzyme linked immunosorbent assay (ELISA) using axenic Giardia lamblia whole trophozoites as antigen for routine serodiagnosis of Giardia infection. Detection of anti-Giardia IgM antibody was found to be useful in the early detection of symptomatic giardiasis, whereas IgG detection was not, since the latter could not discriminate between present infection and previous exposure. A mean optical density (OD) +/- 2 standard deviation (SD) value of 0.088 at 1:100 serum dilution was found optimal for the detection of anti-Giardia IgM antibodies as it completely separated out the acute Giardia cases from the Giardia-free controls. The same sera did not reveal any marked differences when tested for anti-Giardia IgG antibodies. Detection of IgM antibodies correlated with high sensitivity and specificity (96%) in an evaluation of a large number of sera collected from Giardia cases and controls.

Metacyclogenesis of Leishmania spp: species-specific in vitro transformation, complement resistance, and cell surface carbohydrate and protein profiles

Metacyclic (stationary) and logarithmic (log) forms of promastigotes of Leishmania donovani and Leishmania major were characterized in several ways. The highly active metacyclic forms were larger with more protein and less carbohydrate. The flagellum increased in length 2.4 times in L. major as compared to 1.8 times in L. donovani. Resistance to complement-mediated lysis by normal human serum of in vitro grown Leishmania promastigotes was related to the species, the growth phase in culture, and also the temperature. Metacyclic forms of both species had a much increased resistance to killing by normal serum at different temperatures. Differences in membrane-exposed carbohydrates were detected by fluorescein-conjugated lectins. Peanut agglutinin and Ulex agglutinin I differentiated log and stationary phase promastigotes of L. major. Higher amounts of acid phosphatase were demonstrated in the metacyclic phase. Differences in polypeptides were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Two polypeptides of approximately 51 and 114 kDa were found exclusively in metacyclic promastigotes of both species, whereas 38- and 23-kDa polypeptides were lost or reduced during transformation from log to metacyclic phase promastigotes of L. donovani. In addition, a 75-kDa polypeptide was expressed only in metacyclic promastigotes of L. major.