Antibodies against protein antigenic sites that are identical in the homologous protein of the immunized animal. Autoreactivity in rabbits of antibodies to sperm-whale myoglobin.

Sequence comparisons between the antigenic sites of sperm-whale myoglobin and the corresponding regions in rabbit myoglobin indicate that rabbits make antibodies to regions of the sperm-whale myoglobin molecule which are identical to the corresponding regions in rabbit myoglobin. Rabbit myoglobin did not precipitate with antisera to sperm-whale myoglobin. However, it exhibited an extensive cross-reaction as demonstrated by its ability to inhibit the precipitin reaction of sperm-whale myoglobin, and on an immunoadsorbent, bound a large amount of antibodies to sperm-whale myoglobin.     

Prediction and conformation by synthesis of two antigenic sites in human haemoglobin by extrapolation from the known antigenic structure of sperm-whale myoglobin.

The complete antigenic structure of sperm-whale myoglobin was previously determined in our laboratory. By structural analogy with myoglobin, two regions in human haemoglobin were predicted to comprise antigenic sites. One region was on the alpha-chain [alpha-(15-23)] and the other on the beta-chain [beta-(16-23)]. These two regions were synthesized, purified and characterized, and their immunochemistry was studied. Each peptide was able specifically to bind considerable amounts of haemoglobin antibodies. In a set of homologous proteins, barring any drastic conformational or electrostatic inductive effects exerted by the substitutions, and allowing for obstruction due to subunit interaction, the determination of the antigenic structure of one protein may serve as a useful starting model for the others.     

Diversity of the antibody response to the different antigenic determinants on the hemagglutinin subunits of influenza viruses.

Sera from rabbits hyperimmunized with hemagglutinin (HA) subunits isolated from the A/Port Chalmers/73 (H3N2)strain of influenza virus showed great differences in their cross-reactions with different strains of influenza virus. In hemagglutination-inhibition tests, some sera reacted to about the same titer with A/Port Chalmers/73 and A/Hong Kong/68 viruses, suggesting that these two strains were very closely related. Other sera, which reacted to high titer with A/Port Chalmers/73 virus, had only a low titer with the Hong Kong/68 strain, suggesting that the two viruses were distantly related. Evidence suggested that these diverse cross-reactions were due to widely different ratios, in the different sera, of antibodies to the "common" and the "specific" antigenic determinants on the HA subunits. Thus, some rabbits gave a stronger response to the "common" determinants than to the "specific", whereas in others, the reverse seemed to be the case. Sera from human volunteers injected with A/Port Chalmers/73 inactivated or subunit influenza virus vaccines, or from people infected with Port Chalmers/73 virus, contained, in most cases, antibodies predominantly to the "common" antigenic determinants on the HA subunits. These sera reacted to higher titer with Hong Kong/68 virus than with the Port Chalmers/73 strain. Absorption of these sera with Hong Kong/68 virus totally removed all detectable antibody, suggesting that they contained no antibody to the "specific" determinants of Port Chalmers/73 HA. Paradoxically, absorption of the sera with Port Chalmers virus did not remove all antibodies, suggesting that the sera contained antibodies to the "specific" determinants on Hong Kong/68 HA.     

Structurally inherent antigenic sites. Localization of the antigenic sites of the alpha-chain of human haemoglobin in three host species by a comprehensive synthetic approach.

The antigenic structure of the alpha-chain of human haemoglobin was studied by a synthetic approach consisting of the synthesis of a series of consecutive overlapping peptides that together systematically represent the entire primary structure of the protein. This approach enabled the identification of a full profile of immunochemically active alpha-chain peptides and the localization of its major 'continuous' antigenic sites. Antibodies to haemoglobin raised in each of three different species (goat, rabbit and mouse) recognize similar sites on the alpha-chain. Further, the molecular locations of these sites coincide with alpha-chain regions extrapolated from antigenic sites of the conformationally similar myoglobin molecule. These findings support our earlier proposed concept of 'structurally inherent antigenic sites', namely that antigenicity is conferred on certain surface regions of proteins by virtue of their three-dimensional locations. Thus the antigenic sites of conformationally related proteins are likely to have similar molecular locations.     

Nearest-neighbour analysis of myoglobin antigenic sites. Nearest-neighbour residues whose replacement can alter the environment of binding-site residue(s) and thus change their characteristics and binding capability.

By using the known antigenic structure of sperm-whale myoglobin previously determined in this laboratory and the X-ray co-ordinates for the myoglobin molecule, we have calculated the nearest-atom distances between each of the residues of the antigenic sites and all the other amino acids of the myoglobin molecule. These calculations have enabled us to identify the nearest-neighbour residues to each of the residues in the five antigenic sites, and which thus describe the immediate molecular environment of the sites. The influences of chemical changes or replacements in these environmental residues on the binding capacity of an antigenic site, when considered together with replacements directly in the antigenic sites, are expected to account for the major effects and will be extremely useful in explaining the cross-reactions of myoglobins from various species. However, it is stressed that the analysis has limitations due to the qualitative estimates of the effects, the influences of substitutions of once-removed or even at more distant locations (especially when they are cumulative) and finally the influences of any conformational re-adjustments when these occur as a result of the replacement(s).     

The B-cell response in lymphoid tissue of mice immunized with various antigenic forms of the influenza virus hemagglutinin.

Protection of BALB/c (H-2d) mice against secondary challenge with influenza A viruses is primarily dependent on appropriate recognition of the hemagglutinin (HA) molecule by effectors of humoral immunity, the B lymphocytes and their product the immunoglobulin molecules. The influence of the antigenic form of the HA in eliciting protective antibodies is not clearly defined. We directly monitored the kinetics, character, localization, and helper T-cell dependence of the primary antibody-forming cell (AFC) response and the development of B-cell memory in lymphoid tissues associated with the upper and lower respiratory tracts, and in the spleen and bone marrow, to three forms of HA with various degrees of antigenic organization. Our results show that the antigenic organization of HA substantially influences B-cell immunity, namely, the capacity to generate both primary AFCs and memory B cells responsive to lethal challenge. Immunization by infection is the most efficient means of generating protective memory B cells, in contrast to subunit vaccine. The data also indicate that memory AFCs are predominantly localized to the regional lymphoid tissue where challenge HA is found, unlike primary AFCs, which are restricted to the priming site and which require in vivo CD4+ T-cell help.     

The expression of Ia antigenic determinants on macrophages required for the in vitro antibody response.

A subpopulation of antigen-presenting macrophages required for an in vitro antibody response to burro erythrocytes was deleted by pretreating the splenic macrophages with anti-Ia serum and complement (C). The in vitro response of the macrophage depleted T-B cell population could not be restored by the addition of macrophages resistant to anti-Ia antibodies and C (Ia-). The response of Ia- macrophages and the macrophage-depleted T-B cells was only reconstituted by the addition of Ia+ macrophages. Macrophages pretreated with anti-Ia antibodies restricted to react with determinants of one I subregion could not support the in vitro antibody response when added to cultures whose macrophages were pretreated with anti-Ia serum and C specific for the I-J subregion. These results confirmed that Ia determinants of the I-A, the I-E, and the I-C subregions were all expressed on the I-J+ macrophage required for an in vitro antibody response.     

Analysis of nonmethylated GATC sites in the Escherichia coli chromosome and identification of sites that are differentially methylated in response to environmental stimuli.

Seven GATC sites that are nonmethylated in logarithmic growth phase cells using glycerol as a carbon source were isolated from the Escherichia coli chromosome. Three of these GATC sites are located upstream of the operons gut, mtl, and ppiA, whereas DNA sequences adjacent to three other nonmethylated GATC sites are not homologous to previously identified genes. The seventh nonmethylated GATC site is located downstream of uspA. The protection of this site from DNA methylation requires leucine-responsive regulatory protein and is leucine responsive. The carbon source and the growth phase influenced the protection of the GATC site 5' of the ppiA gene. The other five sites were protected under all the environmental conditions examined.     

Hapten-IgG-induced suppression of the in vitro antibody response: role of hapten density and of antigenic challenge.

We have studied the suppression of the in vitro antibody response of mouse spleen cells to the trinitrophenyl (TNP) hapten by conjugates of TNP-human IgG (TNP-HGG). Normal mouse spleen cells were incubated with conjugates of HGG and of HGG fragments, with different hapten densities. They were then challenged with either a T-dependent or a T-independent antigen. Highly substituted (12 mol of TNP/mol of HGG) conjugates induced a dose-dependent suppression, apparent after short-term incubation at 4 °C, of both T-dependent and T-independent responses. Conjugates of Fab′₂ and Fab′ were as suppressive as conjugates of IgG, whereas conjugates of albumin, aggregated IgG, and β2 microglobulin lacked suppressive activity. In contrast, the lightly substituted conjugates TNP₈-HGG and TNP₂-Fab′₂ induced a time-dependent suppression, affecting only the T-dependent response. This suggests that the suppressive effect of hapten-IgG conjugates is mediated by two different mechanisms according to the density of hapten on the IgG carrier. When these conjugates are used as tolerogens in the in vivo situation, both mechanisms would operate to a variable extent, and this could account for the remarkable tolerogenic properties of hapten-IgG conjugates.     

DNA rearrangements and antigenic variation in Trypanosoma equiperdum: multiple expression-linked sites in independent isolates of trypanosomes expressing the same antigen.

African trypanosomes resist the immune response of their mammalian hosts by varying the surface glycoprotein which constitutes their antigenic identity. The molecular mechanism of this antigenic variation involves the successive activation of a series of genes which code for different variant surface glycoproteins (VSGs). We have studied the expression of two VSG genes (those of VSG-1 and VSG-28) in Trypanosoma equiperdum, and we report the following findings. (i) The expression of both VSG genes is associated with the duplication and transposition of corresponding basic copy genes. (ii) The duplicated transposed copy appears to be the expressed copy. (iii) Although there are multiple genes which cross-hybridize with the VSG-1 cDNA probe, only one of these appears to be used as a template for the expression-linked copy in four independent BoTat-1 clones. (iv) Analysis of the genomic environments of the expressed VSG-1 genes from each of four independently derived BoTat-1 trypanosome clones revealed that there are at least three different sites into which the expression-linked copy can be inserted.     

Analysis of the heat-shock response displayed by two Chaetomium species originating from different thermal environments.

Three features of the heat shock response, reorganization of protein expression, intracellular accumulation of trehalose, and alteration in unsaturation degree of fatty acids were investigated in the thermophilic fungus Chaetomium thermophile and compared to the response displayed by a closely related mesophilic species, C. brasiliense. Thermophilic heat shock response paralleled the mesophilic response in many respects like (i) the temperature difference observed between normothermia and the upper limit of translational activity, (ii) the transient nature of the heat shock response at the level of protein expression including both the induction of heat shock proteins (HSPs) as well as the repression of housekeeping proteins, (iii) the presence of representatives of high-molecular-weight HSPs families, (iv) intracellular accumulation of trehalose, and finally (v) modifications in fatty acid composition. On the other hand, a great variability between the two organisms was observed for the proteins expressed during stress, in particular a protein of the HSP60 family that was only observed in C. thermophile. This peptide was also present constitutively at normal temperature and may thus fulfil thermophilic functions. It is shown that accumulation of trehalose does not play a part in thermophily but is only a stress response. C. thermophile contains less polyunsaturated fatty acids at normal temperature than C. brasiliense, a fact that can be directly related to thermophily. When subjected to heat stress, both organisms tended to accumulate shorter and less unsaturated fatty acids.     

Antigenic structure of human haemoglobin. Localization of the antigenic sites of the beta-chain in three host species by synthetic overlapping peptides representing the entire chain.

A comprehensive synthetic approach is applied here to localize the continuous antigenic sites of the beta-chain of haemoglobin. The approach was based on the synthesis and purification of the following consecutive 15-residue peptides (each overlapping by five residues at both ends with the peptides preceding it and following it in the sequence): 1-15, 11-25 etc. Quantitative radiometric titrations of protein and peptide adsorbents were performed with 125I-labelled anti-haemoglobin antibodies from three different host species. The specificity of antibody binding to peptide adsorbents was confirmed by inhibition studies and by the binding specificity of antibodies isolated from peptide adsorbents. These studies established the full profile of antigenic beta-chain regions, which was found to be independent of the host species. Five major antigenic sites were localized, and their three-dimensional and structural characteristics are discussed in relation to the immune recognition of haemoglobin and other proteins.     

The postnatal development of benzodiazepine receptor sites in the chick optic lobe is modulated by environmental lighting.

The present paper describes the ability of benzodiazepine receptor sites to undergo light mediated-plastic changes during the early postnatal development of the chick optic lobe. The postnatal development pattern of these receptors was studied under different levels of light stimulation, i.e. normal-, light-and dark-rearing. At hatching the specific binding of [3H]Flunitrazepam was 0.23 +/- 0.01 pmol/mg protein. The developmental profile shows a sharp and transient peak of receptor overexpression between the 1st and the 2nd postnatal day in three experimental groups. Between the 2nd and the 6th day significant differences were found between the three groups, being this difference maximal during the peak of overexpression. In fact, on the 2nd day the specific [3H]Flunitrazepam binding showed an increase of 17% (P < 0.0005) and a decrease of 34% (P < 0.0005) for light- and dark-reared animals as compared with normally-reared ones. The changes in receptor density were transient since from the 6th day onward they gradually disappeared, being almost identical in the three groups by the day 15. At this moment the number of benzodiazepine receptor sites stabilized at the adult level. Scatchard analysis at the 2nd postnatal day revealed that the differences observed in the high affinity benzodiazepine binding sites between the three groups were due to modifications in the total number of binding sites while the affinity remained unchanged. The maximal number of binding sites were: 2.76 +/- 0.03, 3.40 +/- 0.01 and 1.46 +/- 0.11 pmol/mg protein in normally-, light- and dark-reared chicks, respectively; while the apparent dissociation constants were unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)