Immunologic modeling of a 75-kDa malarial protein with carrier-free synthetic peptides

Identification, diagnostic potential, and natural expression of immunodominant seroreactive peptides encoded by five Mycobacterium tuberculosis-specific genomic regions

Comparative genomic studies have identified several Mycobacterium tuberculosis-specific genomic regions of difference (RDs) which are absent in the vaccine strains of Mycobacterium bovis BCG and which may be useful in the specific diagnosis of tuberculosis (TB). In this study, a total of 775 synthetic peptides covering the sequences of 39 open reading frame (ORF) proteins encoded by genes predicted in five RDs of M. tuberculosis, i.e., RD1, RD4, RD5, RD6, and RD7, were tested by enzyme-linked immunosorbent assays for antibody reactivity with sera from HIV-negative pulmonary TB patients (n = 100) and M. bovis BCG-vaccinated healthy subjects (n = 100). The results identified three immunodominant peptides reactive with TB sera, i.e., amino acids (aa) 346 to 370 of RD1ORF Rv3876, aa 241 to 265 of RD6ORF Rv1508c, and aa 325 to 336 of RD6ORF Rv1516c. These peptides had significantly stronger antibody reactivity with sera from TB patients than with sera from healthy subjects (P < 0.05) and significantly higher rates of positivity with TB sera (positives = 66 to 93%) than sera from healthy subjects (positives = 10 to 28%). Antipeptide antibodies were raised in rabbits after immunization with pools of 11 peptides corresponding to each protein. Probing of culture filtrates and whole-cell lysates of M. tuberculosis with antipeptide antibodies suggested the natural expression of Rv1516c in whole-cell lysates of M. tuberculosis. The results suggest the potential of the identified immunodominant RD peptides in the serodiagnosis of TB.

Molecular cloning and characterization ofEchinostoma caproniheat shock protein-70 and differential expression in the parasite derived from low- and high-compatible hosts

We cloned and expressedEchinostoma caproniHSP70 inEscherichia coli. This molecule presents an open reading frame (ORF) of 655 amino acids, and a theoretical molecular weight of 71 kDa.E. caproniHSP70 protein showed a high homology to other helminth molecules, major differences being located in the C-terminal region of the molecule, with a hydrophobic portion. Studies of protein and messenger RNA (mRNA) expression revealed a distinct pattern, depending on the host (low- or high-compatible). Specific polyclonal antisera raised against the recombinant protein expressed inEscherichia colidemonstrated its selective presence in excretory/secretory products (ESP) of adult parasites obtained from high-compatible hosts. Immunological studies showed clearly the association of HSP70 with the parasite surface and other structures, including eggs.

Molecular and immunological characterization of the C-terminal region of a new Echinococcus granulosus Heat Shock Protein 70

By screening an expression library of Echinococcus granulosus with IgE from sera of patients with cystic echinococcosis (CE) and allergic reactions, we isolated the C-terminal region of a new heat shock protein (HSP)70 of E. granulosus. The protein, named Eg2HSP70, has close homology with the C-terminal region of Dermatophagoides farinae and human HSP70. We investigated the humoral and cell-mediated immune responses to this antigen in patients with CE grouped according to the presence of allergic reactions. Immunoblotting detected total IgG, IgG4 and IgE specific to Eg2HSP70 (83% of sera contained IgG, 31% IgG4 and 57% IgE). No significant difference was found in immunoglobulin percentages according to the presence of allergic reactions. Immunoblotting inhibition showed that no IgG or IgE specific to Eg2HSP70 cross-reacted with D. farinae or human HSP70. Eg2HSP70-stimulated PBMC from 26 patients produced significantly greater amounts of TNF-alpha, IFN-gamma, and IL-10 than unstimulated cultures in all patients, irrespective of the presence of allergic reactions (P < 0.05). They also produced significantly greater amounts of IL-4 than unstimulated cultures exclusively in patients with allergic reactions (P < 0.05). These findings show that Eg2HSP70 is a new antigenic molecule inducing both B and T cell responses.

Cytokines, nitric oxide, heat shock proteins and virulence in Toxoplasma

Elucidating the factors that play important roles in the expression of virulence by parasites is crucial to understanding disease pathogenesis and to developing control strategies rationally. Here, Kate Miller, Nick Smith and Alan Johnson, using Toxoplasma gondii as a model, argue that the interactions between the immune system and 70 kDa heat shock proteins of apicomplexan parasites profoundly influence parasite virulence.

Gene sequence and transcription differences in 70 kDa heat shock protein correlate with murine virulence of Toxoplasma gondii

This study compared the genes encoding cytoplasmic 70 kDa heat shock protein in virulent and avirulent strains of Toxoplasma gondii, to determine whether differences may contribute to the variation in protein expression levels previously reported for this protozoan parasite. A T. gondii PCR probe with homology to Eimeria acervulina cytoplasmic 70 kDa heat shock protein was used to screen a genomic DNA mini-library and isolate the gene from the virulent RH strain. The entire coding region was subsequently amplified from the avirulent ME49 strain by PCR. Alignment of the gene sequences revealed that the virulent RH strain had four copies of a seven-aa repeat unit (GGMPGGM) at the 3'- end of the gene compared with five copies in the avirulent ME49 strain. Comparison of this region among other virulent and avirulent strains revealed that this difference was consistent with virulence. Copy number estimation revealed that this gene is single-copy in both the RH and the ME49 strains. Analysis of mRNA expression revealed a 1.5- to 2-fold increase in transcription of this gene in virulent strains when compared with avirulent strains. For each strain, mRNA was observed at similar levels whether grown in vivo or in vitro. Also, heat-shock treatment of tachyzoites prior to harvest did increase mRNA levels in vitro. This suggests that post-transcriptional regulation of cytoplasmic 70 kDa heat shock protein may occur in T. gondii. Differences in cytoplasmic 70 kDa heat shock protein have been demonstrated at genomic and transcriptional levels in virulent strains compared with avirulent strains, suggesting that this 70 kDa heat shock protein may play an important role in the virulence of T. gondii.

Structure and self assembly of a retrovirus (FeLV) proline rich neutralization domain

The 60 amino acid proline-rich neutralization domain of the external surface unit glycoprotein of feline leukemia virus was chemically synthesized in total and in fragments. We examined the ability of these retroviral peptides to form ordered conformations using 1H-NMR, circular dichroism spectroscopy, and intrinsic viscosity measurements. One dimensional nuclear magnetic resonance spectroscopy revealed that the 60 amino acid peptide could form a stable, folded structure that was long-lived, as shown by the ability to protect amide-protons in D20. Peptides corresponding to the N-terminal 42, N-terminal 20 amino acids, and middle 20 amino acid sections could also form stable structures. The C-terminal segment did not protect any protons in D20. Interestingly, self assembly of the N-terminal 42 and C-terminal 16 amino acid peptides into a structure very close to that of the 60 amino acid domain was observed. The circular dichroism results reveals a large negative cotton effect at 198 nm that is characteristic of the proline-rich beta-turn helixes which consist predominantly of trans-proline. The intrinsic viscosity results suggest a non-random coil structure that is rod shaped. Our conclusion is that PRN60 forms a beta-turn helix and that this region of FeLV-gp70 is a separate folding domain of the retroviral surface unit glycoprotein. The unique conformational properties of PRN60 and its critical role as the predominant target for neutralizing antibody responses suggest that this peptide is a reasonable candidate for producing a synthetic peptide vaccine for FeLV.

Synthetic immunogens. The effect of the conformational space on biological and immunological responses to dimeric hormone constructs

Chimeras of the double chain bis-cystinyl hinge fragment 225-232/225'-232' of the human IgG1 and of peptides related to human little-gastrin were synthesized, whereby the fully bioactive gastrin sequences 2-17 and 5-17 were amide-bond-linked N- and N- or C-terminally, respectively, to the hinge peptide. All the dimeric constructs proved to be efficient immunogens; however, both the configuration of the constructs and the length of the haptenic gastrin molecule were found to drastically affect the specificity of the antibody response and, thus, the type of dominant immune epitope expressed. The different degree of accessibility of the gastrin chains in the dimers is similarly reflected by their binding affinities to gastrin receptors and their bioactivities in vivo. Molecular dynamics simulations of the chimeric compounds clearly revealed that the conformational space of the gastrin peptide chains 2-17 and 5-17 is strongly restricted upon linkage to the hinge peptide. Only in the gastrin-(2-17) construct does sufficient free conformational space seem to be retained, at least for one of the two gastrin chains, in order to allow folding into the bioactive structure. This also agrees with the observation that the dimeric gastrin-(2-17) behaves like a gastrin monomer in terms of receptor binding affinity and biopotency in vivo; but it could additionally explain why an antibody response of gastrin receptor-like specificity could only be induced with this construct. The experimental data may therefore suggest a high degree of parallelism between the mechanism of recognition of the gastrin peptides in the dimeric constructs as hormonal ligands by the gastrin receptors and as haptens by the immune competent cells.