Membrane proteins and their antigenicity of Toxoplasma gondii

Partially purified Toxoplasma gondii antigens by immunoaffinity chromatography

Tachyzoite antigens of Toxoplasma gondii (RH) were partially purified by immunoaffinity chromatography. The cultivated Toxoplasma in vivo (mouse) and in vitro (Hep-2 cell) and peritoneal fluid of T. gondii infected mice were collected for antigen analysis. Tachyzoite antigens collected from infected mouse showed positive bands of 76 kDa, 70 kDa, 64 kDa, 53 kDa, 46 kDa, 44 kDa, 41 kDa, 35 kDa, 25 kDa, 18 kDa, and 13 kDa on immunoblot with anti-Toxoplasma rabbit sera, and those from infected Hep-2 cells revealed reactive bands of 70 kDa, 64 kDa, 53 kDa, 35 kDa 28 kDa, and 13-10 kDa. After applying to an IgG-Sepharose column, two elution peaks, E-1 and E-2 fractions, were obtained from both soluble antigen of T. gondii and the peritoneal fluid of infected mice, respectively. Immunoblots of soluble antigen with immunized rabbit sera revealed positive bands of 97 kDa, 63 kDa, 53 kDa, and 35 kDa from E-1 fraction and 53 kDa and 35 kDa from E-2. In the case of the eluted peaks from mice peritoneal fluid, E-1 showed protein bands of 84 kDa, 76 kDa, 53 kDa, and 29 kDa bands and 53 kDa and 45 kDa from E-2 on immunoblots. Serum IgG antibody titer of mice immunized with T. gondii tachyzoites was increased on 1 week after booster immunization when analysed by ELISA using crude antigen, while it was elevated on 3 weeks after booster immunization by ELISA using purified antigen.

Analysis of antigenic domain of GST fused major surface protein (p30) fragments of Toxoplasma gondii

Antigenic domain of major surface protein (p30) of Toxoplasma gondii was analyzed after polymerase chain reaction (PCR) of its gene fragments. Hydrophilic or hydrophobic moiety of amino acid sequences were expressed as glutathione S-transferase (GST) fusion proteins. Fragments of p30 gene were as follows: T37, total p30 open reading frame (ORF); S28, total ORF excluding N-terminal signal sequence and C-terminal hydrophobic sequence: A19, N-terminal 2/3 parts of S28; P19, C-terminal 2/3 of S28; X9, N-terminal 1/3 part of S28; Y10, middle 1/3 of S28; and Z9, C-terminal 1/3 of S28, respectively. Primer of each fragment was synthesized to include clamp sequence of EcoR I restriction site. PCR amplified DNA was inserted into GST (26 kDa) expression vector, pGEX-4T-1 to transform into Escherichia coli (JM105 strain). GST fusion proteins were expressed with IPTG induction as 63, 54, 45, 45, 35, 36, and 35 kDa proteins measured by SDS-PAGE. Each fusion protein was confirmed with GST detection kit. Western blot analysis with the serum of a toxoplasmosis patient revealed antigenicity in proteins expressed by T37, S28, and A19 but not those by P18, X9, Y10, and Z9. Antigenicity of p30 seems to be located either in N-terminal 1/3 part in the presence of middle 1/3 part or in the oligopeptides between margins of the first and second 1/3 parts.

[Antigen analysis of Toxoplasma gondii lysate and excretory-secretory materials by enzyme-linked immunoelectrotransfer blot (EITB)]

Recently, the importance of toxoplasmosis is raised as a complication in immunosuppressed or AIDS patients. Our study focused on the identification of a variety of Toxoplasma antigens by immunoblotting. Rabbits and BALB/c mice were immunized with Toxoplasma lysate (RH strain), frozen tachyzoites (RH strain) or cysts (Beverly and Fukaya strain). Blood were collected from ear vein, heart or orbital plexus for detecting the serum antibody levels. For excretory-secretory (E.S) antigens, T. gondii (RH) tachyzoite were cultured in CHL (Chinese hamster lung) cells with MEM containing of 5% FCS. After 72 hrs, culture supernatant was collected. BALB/c mice were inoculated with RH tachyzoite intraperitoneally and peritoneal fluids were extracted three days later. E.S antigens were detected in culture supernatant and infected mouse peritoneal fluid by EITB. Serum IgG levels in rabbit were 1:512 of 10 days after primary immunization, 1:2,048 of 10 days after secondary immunization, 1:1,024 of 20 days after secondary immunization by IFAT, respectively. Serum IgG levels of immunized mice were 1:128 after 7 weeks. Tachyzoite antigens of the RH strain were detected 25 protein bands ranging 10 kDa-220 kDa of molecular weights with Coomassie blue stain. Toxoplasma major antigens corresponding to MW of 24 kDa, 27 kDa, 30 kDa, 35 kDa, 38 kDa were recognized by IgG and IgM antibodies. Excretory-secretory antigens present in culture supernatant with M. W. of 20, 30 kDa and in infected mouse peritoneal fluid with M.W. of 33 (P30), 45 kDa. When RH tachyzoite antigen was probed with different mice sera immunized with 2 strains of T. gondii, the IgG antibody band of Fukaya and Beverly strain (8 week-serum) is identical to those of RH strain. It is considered that the 30 kDa polypeptide detected in excretory-secretory materials and lysate was important major antigen of T. gondii (RH).