Genetic and antigenic variation of capsid protein VP7 of serotype G1 human rotavirus isolates.
(1/863)
The deduced amino acid sequences of the outer capsid protein, VP7, of serotype G1 rotavirus clinical isolates collected over a 6 year period (1990-1995) in Melbourne, Australia, were examined. Phylogenetic analysis characterized the sequences into two discrete clusters representing two of the four global lineages of human G1 VP7 proteins. Antigenic characterization using a panel of serotype G1-specific neutralizing monoclonal antibodies classified lineage II isolates (1990-1993) as monotype G1a while lineage I isolates were classified as monotype G1b (1993-1995). Examination of the sequences of the neutralization epitope regions of VP7 revealed a particular amino acid substitution at residue 94 in region A (Asp --> Ser/Thr) that correlated with lineage and monotype designation. Our results indicated that temporal genetic variation of the VP7 of serotype G1 rotaviruses was associated with changes in the antigenicity of these isolates. (+info)
The major immunogenic epitopes of Epstein-Barr virus (EBV) nuclear antigen 1 are encoded by sequence domains which vary among nasopharyngeal carcinoma biopsies and EBV-associated cell lines.
(2/863)
Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA-1) is a protein expressed consistently in EBV-infected cells and EBV-associated malignant tissues. A panel of monoclonal antibodies (MAbs) was generated against the C terminus of EBNA-1 and evaluated for the detection of EBNA-1 in different cell lines. The epitopes recognized were mapped. Since sequence variations of EBNA-1 have been reported in nasopharyngeal carcinoma (NPC) tissues and in infected healthy individuals, the ability of these MAbs to recognize a recombinant protein derived from an NPC biopsy was also analysed. MAb 4H11 appeared to react with EBNA-1 sequences from different sources, whereas MAbs 5C11, 5F12 and 8F6 failed to recognize a recombinant EBNA-1 protein cloned from an NPC patient. Using different recombinant EBNA-1 fragments in an immunoblot format, this study demonstrates that the domain bounded by amino acids 408 and 498 is very immunogenic in mice in that epitopes in this region are recognized by various MAbs. Amino acid sequences of EBNA-1 were also deduced from nucleotide sequences amplified from three Burkitt's lymphoma cell lines, two spontaneous lymphoblastoid cell lines, two NPC biopsies and one NPC hybrid cell line, NPC-KT, and compared to the sequence from B95-8. The amino acid sequence of EBNA-1 in Akata is almost identical to that in an NPC biopsy, except for amino acid 585. The results of this study indicate that the immunogenic epitopes of EBNA-1 are highly variable. (+info)
Antigenic variation in malaria: a 3' genomic alteration associated with the expression of a P. knowlesi variant antigen.
(3/863)
Antigenic variation of malaria parasites was discovered in P. knowlesi, using a schizont-infected cell agglutination (SICA) assay to detect variant antigens expressed at the surface of infected erythrocytes. Later studies utilizing stable clones, Pk1(A+) and its direct derivative, Pk1(B+)1+, showed that SICA[+] clones express distinct parasite-encoded antigens of approximately 200 kDa. Here we identify a P. knowlesi variant antigen gene and cDNA and demonstrate that it encodes the 205 kDa variant antigen expressed by B+ parasites. This gene belongs to a multigene family, which we term SICAvar. Its ten-exon structure with seven cysteine-rich coding modules is unique compared to P. falciparum var genes. Further, we highlight a 3' genomic alteration that we predict is related to SICAvar gene switching. (+info)
Phase variations of the Mycoplasma penetrans main surface lipoprotein increase antigenic diversity.
(4/863)
Mycoplasma penetrans is a recently identified mycoplasma, isolated from urine samples collected from human immunodeficiency virus (HIV)-infected patients. Its presence is significantly associated with HIV infection. The major antigen recognized during natural and experimental infections is an abundant P35 lipoprotein which, upon extraction, segregates in the Triton X-114 detergent phase and is the basis of M. penetrans-specific serological assays. We report here that the P35 antigen undergoes spontaneous and reversible phase variation at high frequency, leading to heterogeneous populations of mycoplasmas, even when derived from a clonal lineage. This variation was found to be determined at the transcription level, and although this property is not unique among the members of the class Mollicutes, the mechanism by which it occurs in M. penetrans differs from those previously described for other Mycoplasma species. Indeed, the P35 phase variation was due neither to a p35 gene rearrangement nor to point mutations within the gene itself or its promoter. The P35 phase variation in the different variants obtained was concomitant with modifications in the pattern of other expressed lipoproteins, probably due to regulated expression of selected members of a gene family which was found to potentially encode similar lipoproteins. M. penetrans variants could be selected on the basis of their lack of colony immunoreactivity with a polyclonal antiserum against a Triton X-114 extract, strongly suggesting that the mechanisms involved in altering surface antigen expression might allow evasion of the humoral immune response of the infected host. (+info)
Molecular and functional analysis of a conserved CTL epitope in HIV-1 p24 recognized from a long-term nonprogressor: constraints on immune escape associated with targeting a sequence essential for viral replication.
(5/863)
It has been hypothesized that sequence variation within CTL epitopes leading to immune escape plays a role in the progression of HIV-1 infection. Only very limited data exist that address the influence of biologic characteristics of CTL epitopes on the emergence of immune escape variants and the efficiency of suppression HIV-1 by CTL. In this report, we studied the effects of HIV-1 CTL epitope sequence variation on HIV-1 replication. The highly conserved HLA-B14-restricted CTL epitope DRFYKTLRAE in HIV-1 p24 was examined, which had been defined as the immunodominant CTL epitope in a long-term nonprogressing individual. We generated a set of viral mutants on an HX10 background differing by a single conservative or nonconservative amino acid substitution at each of the P1 to P9 amino acid residues of the epitope. All of the nonconservative amino acid substitutions abolished viral infectivity and only 5 of 10 conservative changes yielded replication-competent virus. Recognition of these epitope sequence variants by CTL was tested using synthetic peptides. All mutations that abrogated CTL recognition strongly impaired viral replication, and all replication-competent viral variants were recognized by CTL, although some variants with a lower efficiency. Our data indicate that this CTL epitope is located within a viral sequence essential for viral replication. Targeting CTL epitopes within functionally important regions of the HIV-1 genome could limit the chance of immune evasion. (+info)
Spontaneous regression of primary autoreactivity during chronic progression of experimental autoimmune encephalomyelitis and multiple sclerosis.
(6/863)
Experimental autoimmune encephalomyelitis (EAE) is a widely used animal model for multiple sclerosis (MS). EAE is typically initiated by CD4(+) T helper cell type 1 (Th1) autoreactivity directed against a single priming immunodominant myelin peptide determinant. Recent studies have shown that clinical progression of EAE involves the accumulation of neo-autoreactivity, commonly referred to as epitope spreading, directed against peptide determinants not involved in the priming process. This study directly addresses the relative roles of primary autoreactivity and secondary epitope spreading in the progression of both EAE and MS. To this end we serially evaluated the development of several epitope-spreading cascades in SWXJ mice primed with distinctly different encephalitogenic determinants of myelin proteolipid protein. In a series of analogous experiments, we examined the development of epitope spreading in patients with isolated monosymptomatic demyelinating syndrome as their disease progressed to clinically definite MS. Our results indicate that in both EAE and MS, primary proliferative autoreactivity associated with onset of clinical disease invariably regresses with time and is often undetectable during periods of disease progression. In contrast, the emergence of sustained secondary autoreactivity to spreading determinants is consistently associated with disease progression in both EAE and MS. Our results indicate that chronic progression of EAE and MS involves a shifting of autoreactivity from primary initiating self-determinants to defined cascades of secondary determinants that sustain the self-recognition process during disease progression. (+info)
Antigenic heterogeneity of the hepatitis C virus NS4 protein as modeled with synthetic peptides.
(7/863)
The effect of sequence heterogeneity on the immunologic properties of two strong antigenic regions of the hepatitis C virus (HCV) NS4 protein was studied by using a set of 443 overlapping 20-mer synthetic peptides. One antigenic region comprising the cleavage site between NS4a and NS4b (region 5-1-1) was modeled with peptides derived from 73 different known sequences, representing HCV genotypes 1-6. The other antigenic region, designated region 59 and located at the C-terminus of the NS4b protein, was modeled with peptides from 7 known sequences representing genotypes 1-3. All peptides were tested for antigenic reactivity by enzyme immunoassay with a panel of anti-HCV-positive serum specimens representing genotypes 1-5. The data demonstrated that immunoreactive peptides fell into two groups. One group, represented by N-terminal peptides, demonstrated genotype-independent immunoreactivity; the other group, from the central part of region 5-1-1, showed strict genotype specificity. Nineteen peptides from the genotype-independent group strongly immunoreacted with a wide range of serum samples containing antibodies to all 5 HCV genotypes. Twenty-five peptides from the genotype-specific group were found to strongly react with serum containing antibodies only to the genotype from which the peptides were derived. Similar to the N-terminal part of region 5-1-1, peptides derived from region 59 did not show genotype-specific immunoreactivity. Some peptides derived from the central part of region 59 showed very strong and broad antigenic reactivity. Thus, after examining two antigenic regions of the NS4 protein, we identified short sequences that can be used for the efficient detection of either genotype-independent or genotype-specific HCV antibodies. (+info)
Structural and evolutionary inference from molecular variation in Neisseria porins.
(8/863)
The porin proteins of the pathogenic Neisseria species, Neisseria gonorrhoeae and Neisseria meningitidis, are important as serotyping antigens, putative vaccine components, and for their proposed role in the intracellular colonization of humans. A three-dimensional structural homology model for Neisseria porins was generated from Escherichia coli porin structures and N. meningitidis PorA and PorB sequences. The Neisseria sequences were readily assembled into the 16-strand beta-barrel fold characteristic of porins, despite relatively low sequence identity with the Escherichia proteins. The model provided information on the spatial relationships of variable regions of peptide sequences in the PorA and PorB trimers and insights relevant to the use of these proteins in vaccines. The nucleotide sequences of the porin genes from a number of other Neisseria species were obtained by PCR direct sequencing and from GenBank. Alignment and analysis of all available Neisseria porin sequences by use of the structurally conserved regions derived from the PorA and PorB structural models resulted in the recovery of an improved phylogenetic signal. Phylogenetic analyses were consistent with an important role for horizontal genetic exchange in the emergence of different porin classes and confirmed the close evolutionary relationships of the porins from N. meningitidis, N. gonorrhoeae, Neisseria lactamica, and Neisseria polysaccharea. Only members of this group contained three conserved lysine residues which form a potential GTP binding site implicated in pathogenesis. The model placed these residues on the inside of the pore, in close proximity, consistent with their role in regulating pore function when inserted into host cells. (+info)