Analysis of Immune Responses against T- and B-Cell Epitopes fromPlasmodium falciparumLiver-Stage Antigen 1 in Rodent Malaria Models and Malaria-Exposed Human Subjects in India

Abstract

Liver-stage antigen 1 (LSA-1) is a potential vaccine candidate against preerythrocytic stages of malaria. We report here the immunogenicity of linear synthetic constructs delineated as T H -cell determinants from the nonrepeat regions of Plasmodium falciparum LSA-1 in murine models and human subjects from areas where malaria is endemic in Rajasthan State, India. Seven peptide constructs (LS1.1 to LS1.7) corresponding to predicted T-cell sites from both the N-and C-terminal regions and peptide LS1R from a repeat region of PfLSA-1 were synthesized to analyze the cellular immune responses. These linear peptides were also tested for humoral responses in order to determine if there were any overlapping B-cell epitopes in the predicted T-cell sites. Most peptides induced cellular responses in peptide-immunized BALB/c and C57BL/6 mice as measured by proliferation and cytokine analysis. Cross-reactive T-cell recognition of P. falciparum-based peptides in Plasmodium berghei-immune animals was evaluated, but only one peptide, LS1.2 (amino acids 1742 to 1760) triggered T-cell proliferation and interleukin-2 and gamma interferon secretion in P. berghei-immune splenocytes of BALB/c and C57BL/6 mice as well as in Thamnomys gazellae (natural host of P. berghei ANKA). In an enzyme-linked immunosorbent assay with the peptides, only one peptide, LS1.1, was recognized by anti-P. berghei liver-stage serum. Three peptides (LS1.1, LS1.2, and LS1.3) of the eight peptides tested in this study were recognized by a relatively large percentage of P. falciparum-exposed human subjects; the reactivities ranged from ϳ45% for LS1.3 to ϳ60% for LS1.1 and LS1.2. Interestingly, all of the eight putative T-cell determinants were also recognized by the sera collected from malaria patients, although the response was variable in nature. These T H -and B-cell epitopes may be of potential value for preerythrocytic antigen-based malaria subunit vaccine formulations.

Lymphocyte proliferation and antibody responses to Plasmodium falciparum liver-stage antigen-1 in a highland area of Kenya with seasonal variation in malaria transmission.

“…Studies of residents of South America, Papua New Guinea, India, and Africa have demonstrated varying frequencies of antibodies to LSA-1 synthetic peptides and recombinant proteins. 12,14,18,20,21,24 Unlike the current report, antibodies in these studies were evaluated at only one time point. The frequency of antibodies to LSA-Rep, a sequence that includes the EQ repeat evaluated in the current report, ranged from 17% in a non-immune population that migrated to a malaria- 14,24 Our finding that 32.1% of the individuals had IgG antibodies to a central repeat region peptide is in the mid-range of these prior studies.…”

“…Reports from high transmission areas of India, Gabon, and Papua New Guinea showed that 59-82% of subjects had lymphocyte proliferation responses to LSA-1 peptides. 12,18,21 In contrast, studies examining residents of areas where transmission is low or studies restricting analysis to children who have not recently reported an attack of clinical malaria report lower response rates (6.7-33.1%). 14,20,22 A study of proliferation responses to LSA-1 in an highland area of Madagascar is most comparable to the current data.…”

Usefulness of the recombinant liver stage antigen-3 for an early serodiagnosis of Plasmodium falciparum infection

“…These proteins are both surface proteins, and are expressed solely in infected hepatocytes and thought to have a role in liver schizogony and merozoite release. Specific humoral, cellular, and cytokine immune responses to LSA-1 and LSA-3 are well documented, with epitopes identified that correlate with the antibody production, proliferative T-cell responses, or cytokine induction (Aidoo et al, 2000;Joshi et al, 2000;Perlaza et al, 2001). Both preerythrocyte antigens have been considered to be vaccine candidates against P. falciparum due to their antigenic and protection-inducing immunogenic properties Kurtis et al, 2001;Sauzet et al, 2001;Taylor-Robinson, 2003).…”

“…During this stage, the parasites express liver stage specific antigens. In P. falciparum, at least 2 of the relevant antigens, liver stage antigen-1 (LSA-1) and liver stage antigen-3 (LSA-3), have been identified and characterized (Guerin-Marchand et al, 1987;Aidoo et al, 2000;Joshi et al, 2000). These proteins are both surface proteins, and are expressed solely in infected hepatocytes and thought to have a role in liver schizogony and merozoite release.…”

Vaccination with antioxidant enzymes confers protective immunity against challenge infection with Schistosoma mansoni

“…Analyses of the reactivity of specific antibody isotypes against these peptides were aimed to identify relevant B cell epitopes that could be used in a subunit vaccine (Joshi et al 2000, Tallima et al 2003. Synthetic peptides have been widely used for the evaluation of both B and T cell epitopes responsible for (or that could lead to) protection against other pathogens, including Schistosoma (Reynolds et al 1992, 1994, Eggleton et al 2000, Joshi et al 2000. We demonstrated that BALB/c mice vaccinated with SmCT-SOD developed high levels of antibodies directed mainly to the SmCT-SOD derived peptide 3 (Pep 3), which included amino acid residues 64-83 .…”