ENDOGENOUS CHANGES OF PHOTOCHEMICAL ACTIVITIES OF SPINACH LEAVES

The activities of green cell-free extracts of spinach leavesin performing photochemical transphosphorylation, photosyntheticphosphorylation, the HILL reaction and the light-induced formationof the endogenous reducing substance (ascorbic acid) were followedin parallel during the growth process of the plant. There wasa certain parallelism between the development of the activitiesof photochemical transphosphorylation, of photo-synthetic phosphorylationand of the HILL reaction, activities being low in the earlierstage of growth, reaching a maximum just before efflorescence,and showing thereafter a more or less sharp decline. The activityin the light-induced formation of endogenous reducing substancewas undetectable for the first 35 day-period of growth, reacheda maximum about one week earlier than the other three activities,and again disappeared after 60 days of growth. (Received September 9, 1960; )     

Immunodominant CD4+ T-cell epitope within nonstructural protein 3 in acute hepatitis C virus infection.

In acute hepatitis C virus infection, 50 to 70% of patients develop chronic disease. Considering the low rate of spontaneous viral clearance during chronic hepatitis C infection, the first few months of interaction between the patient's immune system and the viral population seem to be crucial in determining the outcome of infection. We previously reported the association between a strong and sustained CD4+ T-cell response to nonstructural protein 3 (NS3) of the hepatitis C virus and a self-limited course of acute hepatitis C infection. In this study, we identify an immunodominant CD4+ T-cell epitope (amino acids 1248 to 1261) that was recognized by the majority (14 of 23) of NS3-specific CD4+ T-cell clones from four of five patients with acute hepatitis C infection. This epitope can be presented to CD4+ T cells by HLA-DR4, -DR11, -DR12, -DR13, and -DR16. HLA-binding studies revealed a high binding affinity for 10 of 13 common HLA-DR alleles. Two additional CD4+ T-cell epitopes, amino acids 1388 to 1407 and amino acids 1450 to 1469, showed a very narrow pattern of binding to individual HLA-DR alleles. Our data suggest that the NS3-specific CD4+ T-cell response in acute hepatitis C infection is dominated by a single, promiscuous peptide epitope which could become a promising candidate for the development of a CD4+ T-cell vaccine.     

Studies on the flight activity of the Viburnum whitefly, a reluctant flyer

Dispersal of adult Viburnum whitefly,Aleurotrachelus jelinekii (Frauenf.) was assessed over a period of 6 years, both in the field and in the laboratory. Flight activity did not appear to be strongly affected by normal variation in either temperature or windspeed. The aerial density of flying adults decreased rapidly with distance from the host plant. Movement up to 5 m from the host plant was found to be density dependent, although there is no suggestion that longer flights become more frequent at higher population densities. More males were caught at the beginning of the season and the number of males flying increased as the population density rose. Insects were flight mature after about 3 h, but flew readily only after 2 days. Longer flights were observed from younger females at a time when they would move from old to young leaves. Landing site preference was not recorded, which contrasts with the behaviour of the cabbage whitefly. Flight in the Viburnum whitefly appears to redistribute the population within the immediate habitat, but migration did not appear to be a significant demographic factor in the isolated populations studied.

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Etude de l'activité de vold d'Aleurotrachelus jelinekii peu enclin au vol

Résumé La dispersion des adultes d'Aleurotrachelus jelinekii Frauenf, tant dans la nature qu'au laboratoire, a été estimée sur une période de 6 ans. L'activité de vol n'a pas paru être fortement modifiée par les variations de la température et de la vitesse du vent. Le nombre d'adultes en vol a diminué rapidement jusqu'à 5 m de la plante hôte, et il était density-dependent, bien que rien ne prouve que les vols les plus longs deviennent plus fréquents à des densités de population plus élevées. Plus de mâles ont été capturés au début de la saison et le nombre de mâles en vol s'est accru avec la densité de la population. Les insectes étaient aptes au vol 3 heures après la mue imaginale, mais ne volaient normalement que 2 jours après. Les vols les plus longs ont été observés chez les plus jeunes femelles au moment où elles devaient migrer de feuilles âgées à des feuilles jeunes. Les lieux d'atterrissage préférés n'ont pas été décelés. Le vol chezA. jelinekii semble redistribuer la population dans l'habitat immédiat et la migration n'apparaît pas être un paramètre démographique significantif dans les populations isolées étudiées.

     

Effect of pH on MHC class II-peptide interactions.

The effect of pH on class II-peptide interactions has been analyzed using several mouse (IAd, IAk, IEd, IEk) and human (DR1, DR5, DR7) MHC specificities, and eight different class II-restricted determinants. In direct binding assays, acidic conditions led to increased binding capacity for many class II-peptide combinations. IE molecules seemed to bind optimally around pH 4.5, whereas IA molecules displayed binding optima in the 5.5 to 6.5 range. In contrast, the DR molecules studied were, in most cases, affected only marginally by pH changes in the 4.5 to 7.0 range. Despite these apparent isotype-specific trends, no general rule could be formulated, because even for the same class II molecules, the binding capacity could be increased for many peptides when the binding was performed under acidic conditions, was unaffected for some, and even decreased for others. The mechanisms responsible for this complex behavior were analyzed in more detail by kinetic and equilibrium analysis of three different class II-peptide combinations (IAd/OVA 323-339, IAk/HEL 46-61, and DR1/HA 307-319). It was found that acidic pH conditions could affect both on and off rates for class II-peptide complexes. Depending on the net balance of these effects, either increases, decreases, or no effect on overall affinities at equilibrium were detected. In the case of IAd/OVA 323-339, it was also found that acidic conditions influenced the binding capacity of class II molecules by increasing the fraction of sites available for peptide binding, presumably by favoring dissociation of endogenously bound, acid-sensitive peptides.     

Two distinct HLA-A * 0101-specific submotifs illustrate alternative peptide binding modes

 Previous studies have defined two different peptide binding motifs specific for HLA-A ^* 0101. These motifs are characterized by the presence of tyrosine (Y) at the C-termini of 9-mer and 10-mer peptides, and either a small polar or hydrophobic (S, T, M) residue in position 2, or a negatively charged (D or E) residue in position 3. In this study, the structural requirements for peptide binding to A ^* 0101 have been further analyzed by examining the binding capacity of large sets of peptides corresponding to naturally occurring sequences which bore one or the other of these two A ^* 0101-specific motifs. By correlating the presence of specific residue types at each position along the peptide sequence with increased (or decreased) binding affinity, the prominent influence of secondary anchor residues was revealed. In most cases, the two anchors in positions 2 and 3 appear to act synergistically. With the exception of the DE₃ submotif in 9-mer peptides, a positive role for aromatic residues in position 1 and the center of the peptide (positions 4 or 5 of 9- or 10-mer peptides, respectively), and proline at C-3, were also consistently detected. However, secondary anchor residues also appear to differ significantly between the two different submotifs, demonstrating that A ^* 0101 can utilize alternative modes in binding its peptide ligands. According to these analyses, specific refined submotifs were also established, and their merit verified by independent sets of potential A ^* 0101 binding peptides. Besides providing useful insight into the nature of the interaction of the A ^* 0101 allele with its peptide ligands, such refined motifs should also facilitate accurate prediction of potential A ^* 0101-restricted peptide epitopes. Received: 16 July 1996 / Revised: 18 September 1996     

The self-directed T cell repertoire against mouse lysozyme reflects the influence of the hierarchy of its own determinants and can be engaged by a foreign lysozyme.

The T cell repertoire is shaped by the processes of positive and negative selection. We have previously shown that mice are tolerant to a native self-Ag, mouse lysozyme (ML), but they respond vigorously when challenged with different ML peptides ("cryptic" self-determinants). In this study, we have addressed the issue of the physiological significance of both the hierarchy (dominance/crypticity) of self-determinants within ML and the anti-cryptic, self (ML)-directed T cell repertoire. Our results demonstrate that there are several ML peptides that bind well to MHC but are totally nonimmunogenic when tested for proliferative T cell response and cytokine secretion: a subset of these peptides presumably represent the originally dominant self-determinants of ML, which have rendered the T cells tolerant during thymic selection. Other ML peptides, which bind well to MHC and are immunogenic, correspond to the cryptic determinants of ML: T cells against cryptic ML determinants escape tolerance induction. Thus, the mature T cell repertoire against ML bears the direct imprint of the hierarchy of self (ML)-determinants. Interestingly, hen egg white lysozyme could prime T cells in vivo that were cross-reactive with certain cryptic ML determinants, and vice versa, without requiring any coimmunization with the foreign lysozyme and ML peptide(s). Moreover, repeated, deliberate priming and expansion of T cells by hen egg white lysozyme immunization concomitantly enhanced T cell response to such cross-reactive ML determinants. This reciprocal self-foreign determinant cross-reactivity may play a previously unrecognized, but crucial, role in the expansion and diversification of self-reactive clones in the autoimmune response.     

Celiac disease association with CD8+ T cell responses: identification of a novel gliadin-derived HLA-A2-restricted epitope

One of the diagnostic hallmarks of the histological lesions associated with celiac disease is the extensive infiltration of the small intestinal epithelium by CD8(+) T cells of unknown Ag specificity. In this study, we report recognition of the gliadin-derived peptide (A-gliadin 123-132) by CD8(+) T lymphocytes from celiac patients. A-gliadin 123-132-specific IFN-gamma production and cytotoxic activity were detected in PBMCs derived from patients on gluten-free diet, but not from either celiac patients on gluten-containing diet or healthy controls. In contrast, A-gliadin 123-132-specific cells were isolated from small intestine biopsies of patients on either gluten-free or gluten-containing diets. Short-term T cell lines derived from the small intestinal mucosa and specific for the 123-132 epitope recognized human APC pulsed with either whole recombinant alpha-gliadin or a partial pepsin-trypsin gliadin digest. Finally, we speculate on a possible mechanism leading to processing and presentation of class I-restricted gliadin-derived epitopes in celiac disease patients.     

The HLA molecules DQA1*0501/B1*0201 and DQA1*0301/B1*0302 share an extensive overlap in peptide binding specificity

Assays to measure the binding capacity of peptides for HLA-DQA1*0501/B*0201 (DQ2.3) and DQA1*0301/B*0302 (DQ3.2) were developed using solubilized MHC molecules purified from EBV-transformed cell lines. These quantitative assays, based on the principle of the inhibition of binding of a high-affinity radiolabeled ligand, were validated by examining the binding capacity of known DQ-restricted epitopes or ligands. The availability of these assays allowed an investigation of patterns of cross-reactivity between different DQ molecules and with various common DR molecules. DQ2.3 and DQ3.2 were found to have significantly overlapping peptide binding repertoires. Specifically, of 13 peptides that bound either DQ2.3 or DQ3.2, nine (69.2%) bound both. The molecular basis of this high degree of cross-reactivity was further investigated with panels of single substitution analogs of the thyroid peroxidase 632-645Y epitope. It was found that DQ2.3 and DQ3.2 bind the same ligands by using similar anchor residues but different registers. These data suggest that in analogy to what was previously described for HLA-DR molecules, HLA-DQ supertypes characterized by largely overlapping binding repertoires can be defined. In light of the known linkage of both HLA-DQ2.3 and -DQ3.2 with insulin-dependent diabetes mellitus and celiac disease, these results might have important implications for understanding HLA class II autoimmune disease associations.     

Class I molecules with similar peptide-binding specificities are the result of both common ancestry and convergent evolution

HLA class I molecules can be classified into supertypes associated with overlapping peptide-binding motifs and repertoires. Herein, overlaps in peptide-binding and T-cell recognition repertoires were demonstrated between mouse and human molecules. Since rodent and primate lineages separated before the current allelic variation of mouse and human class I molecules, these data demonstrate that supertypic specificities originated by convergent evolution. Phylogenetic and structural analyses demonstrated that convergent evolution also occurs amongst primates and within the human species, resulting from the selection of different pocket structures having similar specificity or independent repeated selection of the same pocket structure.     

An association between the acute phase response and patterns of antigen induced T cell proliferation in juvenile idiopathic arthritis

The aim of this research was to determine whether all memory T cells have the same propensity to migrate to the joint in patients with juvenile idiopathic arthritis. Paired synovial fluid and peripheral blood mononuclear cell proliferative responses to a panel of antigens were measured and the results correlated with a detailed set of laboratory and clinical data from 39 patients with juvenile idiopathic arthritis. Two distinct patterns of proliferative response were found in the majority of patients: a diverse pattern, in which synovial fluid responses were greater than peripheral blood responses for all antigens tested; and a restricted pattern, in which peripheral blood responses to some antigens were more vigorous than those in the synovial fluid compartment. The diverse pattern was generally found in patients with a high acute phase response, whereas patients without elevated acute phase proteins were more likely to demonstrate a restricted pattern. We propose that an association between the synovial fluid T cell repertoire and the acute phase response suggests that proinflammatory cytokines may influence recruitment of memory T cells to an inflammatory site, independent of their antigen specificity. Additionally, increased responses to enteric bacteria and the presence of αEβ7 T cells in synovial fluid may reflect accumulation of gut associated T cells in the synovial compartment, even in the absence of an elevated acute phase response. This is the first report of an association between the acute phase response and the T cell population recruited to an inflammatory site.