Biomedical subjects

C Praud

Publications and source records attributed to C Praud.

4 recordsLinked to original sources

PubMed1996

Role of polymorphic residues of human leucocyte antigen-DR molecules on the binding of human immunodeficiency virus peptides.

A study was made of the binding properties of 96 human immunodeficiency virus peptides to human leucocyte antigen (HLA)-DR1 and HLA-DR103 molecules, which differ by three amino acids at positions 67, 70 and 71 in the beta chains. The affinity of the peptides was characterized by their inhibitory concentrations in competitive binding assays which displace half of the labelled influenza haemagglutinin peptide HA306-318 (IC50). Among the high-affinity peptides (IC50 < or = 1 microM), seven bound to DR1, three to DR103 and five equally well to both alleles (promiscuous peptides). Thirty-two other peptides showed medium or low affinity for DR molecules. The role of polymorphic residues was analysed using six mutated DR molecules, intermediates between DR1 and DR103 and differing by one or two substitutions at positions 67, 70 or 71. We reached the same conclusions when using DR1-specific or DR103-specific peptides: modification of residue 70 had no effect on peptide affinity, but single substitution at positions 67 or 71 decreased the allele specificity of the peptides while double substitution at 67 and 71 completely reversed the peptide specificity. In functional assays, DR-binding peptides are able to outcompete specific T-cell proliferation. Furthermore, modification at position 67 or 70 significantly affects the T-cell response and mutation at position 71 abolishes completely the T-cell proliferation. Thus, the polymorphic positions 67 and 71 contributed to the peptide binding with direct effects on T-cell receptor (TCR) recognition while position 70 seems to be mostly engaged in TCR interactions. Furthermore, our results suggest that polymorphic residues may select allele-specific peptides and also influence the conformation of promiscuous peptides.

Amino Acid Sequence↗

PubMed1995

Microvariation creates significant functional differences in the DR3 molecules.

Two DR3 molecules differ by four amino acids whose side chains point into the DR antigen-binding groove. To begin to assess the role of microvariation on DR3 function, DRB1*0302 residues were replaced with DRB1*0301 residues at beta-chain positions 26, 47, 86, and 47 plus 86. Murine fibroblast cell lines expressing DR(alpha, beta 1*0301), DR(alpha, beta 1*0302), and the four mutant 0302 molecules were examined for alloproliferative DR(alpha, beta 1*0302)-specific TLC stimulation and peptide binding. Changing position 26 had the most profound effect on T-cell recognition (seven of nine TLCs did not respond). Two TLCs did not respond to the mutant 0302V86 molecule and four TLCs that did respond to this mutant lost responsiveness when positions 47 and 86 were mutated together. These data suggest that each of these variant residues, including position 47, influence T-cell recognition. Surprisingly, none of the mutations had an effect on the absolute binding of HA 307-319 (DR[alpha, beta 1*0302] specific) and HSP 3-13 (DR[alpha, beta 1*0301] specific); however, the mutant 0302 molecules changed at position 86 (glycine to valine) consistently bound HA 307-319 at significantly higher levels than DR(alpha, beta 1*0302). These data for position 86 are in contrast to other DR molecules and indicate that peptide contact residues for a specific DR molecule cannot be predicted based on binding results obtained with other DR molecules. These data suggest that each of these variant groove residues, although not accessible to the TCR, contribute to the significant functional differences between the DR3 microvariants through subtle influences on the DR3-peptide complex.

Amino Acid Sequence↗

PubMed1994

Promiscuous and specific binding of HIV peptides to HLA-DR1 and DR103. Impact on T-cell repertoire of nonimmunized individuals.

The binding of immunogenic peptides to DR molecules is influenced by residues that point into the peptide-binding groove. The T-cell response toward a peptide complexed to an MHC molecule depends on the presence of a sufficient number of T cells reactive with peptide-MHC complex on the surface of APCs. From 96 overlapping HIV peptides, we have selected 11 that show a significant binding to either DR1, DR103, or both. These two DR molecules are identical except for three amino acids at positions 67, 70, and 71 on the beta chain. Peptide-specific T-cell lines and clones were generated with cells from nonimmunized donors homozygous for DR1 or DR103 by using either individual peptides or peptide pools for the in vitro priming. Three of the peptides induced T-cell-specific proliferative response in both individuals, and these peptides were not among those with highest affinity. Most of the peptides induced strong responses against autologous APCs. This might reflect cross-reactivity between HIV and self-peptides. Definition of peptides that both show promiscuous binding to DR and elicit a strong T-cell response is important for design of efficient synthetic vaccines.

AIDS Vaccines↗

PubMed1991

Computer-assisted kinetic assay for quantification of total complement activity.

Using apparatus available in any laboratory we developed a semiautomated kinetic technique for complement activity assay. Hemolysis of sensitized red blood cells is performed in the thermostated microflow cell of a spectrophotometer connected to a computer. The computer controls, displays on the screen, and analyzes all the different phases of the assay. After definition of optimal operating conditions, we compared the results obtained by this technique and by Kabat and Mayer's. On 221 patients' sera the regression coefficient was 0.94. The values for samples deficient in one fraction or after in vitro activation were very similar. The coefficient of variation was close to 1% for within series studies and better than 3% between series. This technique is very easy to perform even in a routine nonspecialized laboratory and up to 30-40 sample/h can be tested.

Antibodies↗