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(1/423) Linear peptide specificity of bovine antibody responses to p67 of Theileria parva and sequence diversity of sporozoite-neutralizing epitopes: implications for a vaccine.

A stage-specific surface antigen of Theileria parva, p67, is the basis for the development of an anti-sporozoite vaccine for the control of East Coast fever (ECF) in cattle. By Pepscan analysis with a series of overlapping synthetic p67 peptides, the antigen was shown to contain five distinct linear peptide sequences recognized by sporozoite-neutralizing murine monoclonal antibodies. Three epitopes were located between amino acid positions 105 to 229 and two were located between positions 617 to 639 on p67. Bovine antibodies to a synthetic peptide containing one of these epitopes neutralized sporozoites, validating this approach for defining immune responses that are likely to contribute to immunity. Comparison of the peptide specificity of antibodies from cattle inoculated with recombinant p67 that were immune or susceptible to ECF did not reveal statistically significant differences between the two groups. In general, antipeptide antibody levels in the susceptible animals were lower than in the immune group and neither group developed high responses to all sporozoite-neutralizing epitopes. The bovine antibody response to recombinant p67 was restricted to the N- and C-terminal regions of p67, and there was no activity against the central portion between positions 313 and 583. So far, p67 sequence polymorphisms have been identified only in buffalo-derived T. parva parasites, but the consequence of these for vaccine development remains to be defined. The data indicate that optimizations of the current vaccination protocol against ECF should include boosting of relevant antibody responses to neutralizing epitopes on p67.  (+info)

(2/423) The crystal structure of C-terminal merozoite surface protein 1 at 1.8 A resolution, a highly protective malaria vaccine candidate.

The C-terminal proteolytic processing product of merozoite surface protein 1 (MSP1) appears essential for successful erythrocyte invasion by the malarial parasite, Plasmodium. We have determined the crystal structure at 1.8 A resolution of a soluble baculovirus-recombinant form of the protein from P. cynomolgi, which confers excellent protective efficacy in primate vaccination trials. The structure comprises two EGF-like domains, and sequence comparisons strongly suggest that the same conformation is present in all species of Plasmodium, including P. falciparum and P. vivax, which are pathogenic in man. In particular, conserved interdomain contacts between the two EGF modules should preserve the compact form of the molecule in all species. Implications of the crystal structure for anti-malarial vaccine development are discussed.  (+info)

(3/423) Protective immune responses induced by vaccination with an expression genomic library of Leishmania major.

To develop an effective vaccine against the intracellular protozoan parasite Leishmania spp., we investigated the feasibility of expression library immunization (ELI) in the mouse. Genomic expression libraries of L. major were constructed and used to immunize mice. One of the three libraries (L1, with 10(5) clones) induced a significant protective immune response and delayed the onset of lesion development in highly susceptible BALB/c mice after i.m. immunization, compared with control mice immunized with the empty vector (EV). L1 was then divided into five sublibraries of approximately 2 x 10(4) clones each. Mice immunized with one of the sublibraries (SL1A) developed an even stronger protective effect than that induced by L1. SL1A was further divided into 20 sublibraries (SL2) of approximately 10(3) clones each. One of the SL2 libraries (SL2G) induced a strong protective effect against L. major infection. In direct comparative studies, the protective effect of the sublibraries was in the order of SL2G > SL1A > L1. Lymphoid cells from mice vaccinated with SL2G produced more IFN-gamma and NO, compared with cells from control mice injected with EV. Serum from the vaccinated mice also contained more parasite-specific IgG2a Ab, compared with controls. Therefore, these data demonstrate that ELI is feasible against this complex intracellular parasitic infection, by preferentially inducing the development of Th1 responses. Furthermore, by sequential division of the libraries, this approach may be used to enrich and identify protective genes for effective gene vaccination against other parasitic infections.  (+info)

(4/423) Immunostimulatory DNA as an adjuvant in vaccination against Leishmania major.

Oligodeoxynucleotides (ODN) which contain immunostimulatory CG motifs (CpG ODN) can promote T helper 1 (Th1) responses, an adjuvant activity that is desirable for vaccination against leishmaniasis. To test this, susceptible BALB/c mice were vaccinated with soluble leishmanial antigen (SLA) with or without CpG ODN as adjuvant and then challenged with Leishmania major metacyclic promastigotes. CpG ODN alone gave partial protection when injected up to 5 weeks prior to infection, and longer if the ODN was bound to alum. To demonstrate an antigen-specific adjuvant effect, a minimum of 6 weeks between vaccination and infection was required. Subcutaneous administration of SLA alone, SLA plus alum, or SLA plus non-CpG ODN resulted in exacerbated disease compared to unvaccinated mice. Mice receiving SLA plus CpG ODN showed a highly significant (P < 5 x 10(-5)) reduction in swelling compared to SLA-vaccinated mice and enhanced survival compared to unvaccinated mice. The modulation of the response to SLA by CpG ODN was maintained even when mice were infected 6 months after vaccination. CpG ODN was not an effective adjuvant for antibody production in response to SLA unless given together with alum, when it promoted production of immunoglobulin G2a, a Th1-associated isotype. Our results suggest that with an appropriate antigen, CpG ODN would provide a stable, cost-effective adjuvant for use in vaccination against leishmaniasis.  (+info)

(5/423) Predominance of CD4 Th1 and CD8 Tc1 cells revealed by characterization of the cellular immune response generated by immunization with a DNA vaccine containing a Trypanosoma cruzi gene.

Immunization with a plasmid DNA containing the gene encoding the catalytic domain of trans-sialidase (TS) elicits protective immune responses against experimental Trypanosoma cruzi infection. As several studies provided strong evidence that during infection CD4 Th1 and CD8 T cytotoxic type 1 (Tc1) cells are important factors in host resistance, the present study was designed to evaluate which T-cell types were activated in DNA-vaccinated BALB/c mice. We found that bulk cells from DNA-immunized mice had CD4 and CD8 T cells that produced gamma interferon (IFN-gamma) but not interleukin-4 (IL-4) or IL-10. To characterize the TS-specific T cells at the clonal level, we generated CD4 and CD8 clones. We obtained cytotoxic CD4 clones of the Th1 type that secreted large amounts of IFN-gamma but not IL-4 or IL-10. Unexpectedly, we obtained other CD4 clones with a Th2 phenotype, secreting IL-4 and IL-10 but not IFN-gamma. All CD8 clones were cytotoxic and produced IFN-gamma. IL-4 and IL-10 were not secreted by these cells. Using synthetic peptides, we determined a CD8 epitope recognized by several clones as being represented by amino acids IYNVGQVSI. The antiparasitic activity of a CD4 Th1 and a CD8 Tc1 clone was assessed in vitro. CD4 or CD8 T cells significantly inhibited T. cruzi development in infected macrophages or fibroblasts, respectively. We concluded that DNA vaccine efficiently generates potentially protective CD4 Th1 and CD8 Tc1 cells specific for a T. cruzi antigen, therefore reinforcing the possibility of using this strategy for developing a preventive or therapeutic vaccine against Chagas' disease.  (+info)

(6/423) Protection against toxoplasmosis in mice immunized with different antigens of Toxoplasma gondii incorporated into liposomes.

Different toxoplasma antigens were entrapped within liposomes and evaluated, in this form, for their ability to protect Swiss mice against toxoplasma infection: soluble tachyzoite antigen (L/TAg), tissue cyst (L/CAg), tachyzoite plus tissue cyst (L/TCAg) or purified antigen of tachyzoite (L/pTAg). The protein used in L/pTAg was purified from tachyzoites using a stage-specific monoclonal antibody which reacted at a molecular weight of 32 kD in SDS PAGE and silver stain using reduced condition. To compare the immuno-adjuvant action of liposomes and of Freund's Complete Adjuvant (FCA), another group of mice was immunized with soluble tachyzoite antigen (STAg) emulsified in FCA (FCA/TAg). Control groups were inoculated with (STAg) alone, phosphate-buffered saline (PBS), FCA with PBS (FCA/PBS) and empty liposomes (L/PBS). Mice were inoculated subcutaneously with these antigens six, four and two weeks before a challenge with 80 tissue cysts of the P strain of Toxoplasma gondii orally. All mice immunized with or without adjuvant showed a humoral response, as measured by Elisa. However, no correlation was found between antibody titer and protection against the challenge. All mice immunized with L/pTAg or L/TCAg survived (100), whereas 80% and 90% of mice from groups which received respectively PBS or FCA/PBS and L/PBS died. All mice immunized with antigens entrapped within liposomes (L/TAg, L/CAg, L/TCAg and L/pTAg) showed low numbers of intracerebral cysts.  (+info)

(7/423) A dhfr-ts- Leishmania major knockout mutant cross-protects against Leishmania amazonensis.

E10-5A3 is a dhfr-ts- Leishmania major double knockout auxotrophic shown previously to induce substantial protection against virulent L. major infection in both genetically susceptible and resistant mice. We investigated the capacity of dhfr-ts- to protect against heterologous infection by L. amazonensis. The degree of protection was evaluated by immunization of BALB/c or C57BL/6 mice with E10-5A3, followed by L. amazonensis challenge. Whether immunized by subcutaneous (SC) or intravenous (IV) inoculation, susceptible and resistant mice displayed a partial degree of protection against challenge with virulent L. amazonensis. SC-immunized BALB/c mice developed lesions 40 to 65% smaller than non immunized mice, while IV immunization led to protection ranging from 40 to 75% in four out of six experiments compared to non immunized animals. The resistant C57BL/6 mice displayed comparable degrees of protection, 57% by SC and 49% by IV immunization. Results are encouraging as it has been previously difficult to obtain protection by SC vaccination against Leishmania, the preferred route for human immunization.  (+info)

(8/423) A Plasmodium vivax vaccine candidate displays limited allele polymorphism, which does not restrict recognition by antibodies.

BACKGROUND: The 19 kDa C-terminal region of the merozoite surface protein 1 (MSP1(19)) has been suggested as candidate for part of a subunit vaccine against malaria. A major concern in vaccine development is the polymorphism observed in different plasmodial strains. The present study examined the extension and immunological relevance of the allelic polymorphism of the MSP1(19) from Plasmodium vivax, a major human malaria parasite. MATERIALS AND METHODS: We cloned and sequenced 88 gene fragments representing the MSP1(19) from 28 Brazilian isolates of P. vivax. Subsequently, we evaluated the reactivity of rabbit polyclonal antibodies, a monoclonal antibody, and a panel of 80 human sera to bacterial and yeast recombinant proteins representing the two allelic forms of P. vivax MSP1(19) described thus far. RESULTS: We observed that DNA sequences encoding MSP1(19) were not as variable as the equivalent region of other species of Plasmodium, being conserved among Brazilian isolates of P. vivax. Also, we found that antibodies are directed mainly to conserved epitopes present in both allelic forms of the protein. CONCLUSIONS: Our findings suggest that the use of MSP1(19) as part of a subunit vaccine against P. vivax might be greatly facilitated by the limited genetic polymorphism and predominant recognition of conserved epitopes by antibodies.  (+info)