Circulating lymphocyte subsets after total lymphoid irradiation in chronic progressive multiple sclerosis.
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Adult↗
Biomedical subjects
D Fenoglio
Publications and source records attributed to D Fenoglio.
Role of flanking variable sequences in antigenicity of consensus regions of HIV gp120 for recognition by specific human T helper clones.
Human T helper cells can discriminate among strain variants of HIV gp120 because of T cell clones recognizing non-conserved regions, as demonstrated with T cells from HIV-infected individuals and vaccinated volunteers and with primary T cell lines and clones obtained by in vitro immunization. To obtain a better definition of cross-reactions among T cell determinants within HIV gp120 variants, we used a panel of analog peptides within residues 236-251 from the BRU, MN, SF2 and RF strain sequences to induce primary human T cell lines and clones. Different patterns of response were obtained using each of the analog peptides, although they all share the consensus sequence 246-251. Clones recognizing this sequence were generated by priming with the BRU and RF analog peptides, but not with the SF2 analog peptide. SF2 did not induce any 242-245-specific clones, but only T cells recognizing the 236-240 sequence. A preferential response to residues 236-240 was obtained by priming with the BRU and SF2 peptides, but not with the MN and RF peptides. These results suggest that although the analog peptides exhibit a high degree of homology and share a consensus of the C-terminal sequence (246-251), the T cell response to the conserved sequence 246-251 is controlled by flanking sequences. Therefore the presence of a shared sequence per se does not imply in vitro expansion of clones with that fine specificity, even though such clones are available within the naive repertoire and can be triggered by an analog peptide.
Amino Acid Sequence↗
Frequency of allergen-specific T lymphocytes in blood and bronchial response to allergen in asthma.
BACKGROUND: This study was designed to investigate whether the bronchial response to the sensitizing allergen in asthma is correlated with the frequency of allergen-specific T lymphocytes. METHODS: Twenty-three asthmatic patients sensitized to Dermatophagoides pteryonyssinus who had never received hyposensitizing therapy and 11 healthy control subjects were studied. Allergen-specific T lymphocytes were enumerated in peripheral blood with limiting dilution cultures. Bronchial challenge with methacholine was performed in all subjects; patients with asthma also underwent an allergen bronchial challenge. Correlations between allergen-specific T cell frequencies and nonspecific bronchial hyperresponsiveness to methacholine as independent variables and early and late bronchial responsiveness to allergen challenge as dependent variables were investigated by means of stepwise-multiple regression analysis. RESULTS: We found that the frequency of allergen-specific T lymphocytes was higher than in control subjects in both patients with asthma with (p < 0.001) and those without (p < 0.05) late-phase asthmatic response to allergen. Moreover, the provocative does of allergen necessary to produce an early 15% fall of forced expiratory volume in 1 second could be predicted in part (59%) by an equation that incorporates methacholine sensitivity and allergen-specific T cell frequency. CONCLUSIONS: We conclude that allergen-specific T lymphocytes, which have an established influence on immunoglobulin E production, play an additional role in the induction of the bronchospastic response to inhaled allergen.
Adolescent↗
Non-covalent complexes of HIV gp120 with CD4 and/or mAbs enhance activation of gp120-specific T clones and provide intermolecular help for anti-CD4 antibody production.
The 'dangerous liaison' between CD4 and gp120 that offers the first entry opportunity to HIV may also provoke perturbations of the immune control of the host with far-reaching immunopathological consequences. We wondered whether a mechanism of intermolecular help (T help across the gap of a non-covalent bond, in contrast to the intramolecular help of carrier to hapten) could break self-tolerance and be the cause of the frequent anti-CD4 autoantibodies found in AIDS patients. To determine whether this hypothesis deserves further testing, we designed a series of in vitro and in vivo experiments of increasing complexity, focused on the presentation of gp120 to specific T cells by antigen presenting cells (APC) exposed to the envelope protein in the form of non-covalent complexes. Bi-molecular complexes were constructed by allowing gp120 or gp160 to bind specific human mAbs. Tri-molecular complexes were constructed by introducing CD4 as an intermediate ligand between gp120 and mouse mAbs specific for CD4. In all cases the use of complexes did enhance the immunogenic capacity of substimulatory doses of gp120 or gp160 by facilitating uptake by APC via Fc receptor and consequent presentation to specific human T cell clones. Finally, help for the production in vivo of anti-CD4 antibodies was obtained from T lymphocytes specific for gp120 when CD4-primed memory B cells were pulsed with CD4 complexed with gp120, thus demonstrating in the mouse the entire cycle of intermolecular help via non-covalent interaction, and setting the stage for future experiments on self-tolerance breakage in a human molecular context.
Amino Acid Sequence↗
Kinetic immunodominance: functionally competing antibodies against exposed and cryptic epitopes of Escherichia coli beta-galactosidase are produced in time sequence.
The murine antibody response to Escherichia coli beta-galactosidase (GZ) was analyzed in vivo and in vitro by focusing on two families of antibodies that exert distinct conformational/functional activity on the antigen. Activating antibodies--defined by their capacity to increase the enzymatic activity of defective GZ produced by mutant strains of E. coli--are detected early after secondary challenge. Inhibiting antibodies, which interfere with antibody-mediated enzyme activation, appear later and cause the abrupt fall of activating titer, a scenario suggesting either idiotype/anti-idiotype interaction or opposite pulsions exerted on the antigen molecule. Supporting the latter mechanism, the confrontation of mAbs of the two families produced classical competitive inhibition curves when the readout was enzyme activation, although they recognize two different epitopes of the same molecule: the activating mAb a quaternary conformation-dependent site of wild-type GZ, the inhibiting mAb a sequential determinant exposed only in denatured or in defective enzyme. The different timing of generation of these antibodies during the response may depend on a processing step necessary for unfolding of native antigen and consequent display of certain cryptic epitopes before they can trigger specific B cells. A picture emerges where the response to the various epitopes of a complex antigen is sequentially connected and where the uptake by antigen-presenting cells of antigen complexed with antibodies specific for the exposed epitopes may favor revelation of the cryptic ones.
Animals↗
Novel immunoenzymatic assay for identification of coagulase- and protein A-negative Staphylococcus aureus strains.
A purified monoclonal antibody (MAb) which specifically reacts with Staphylococcus aureus glucosaminidase was obtained. This MAb was utilized to develop an immunoenzymatic assay for the identification of S. aureus strains. The sensitivity of this assay, based on the simultaneous detection of S. aureus glucosaminidase and protein A, was evaluated by analyzing a total of 196 strains, 26 of which did not exhibit one or more of the following properties: protein A, clumping factor, and staphylocoagulase. All strains yielded positive results by the MAb-based immunoenzymatic test. The assay's ability to differentiate between S. aureus and other staphylococci was then analyzed by testing a total of 277 non-S. aureus strains that yielded negative results. Our data demonstrate that this immunoenzymatic assay can be used as a single S. aureus identification criterion, particularly useful for those strains negative for clumping factor, staphylocoagulase, or protein A.
Animals↗
Effect of antigen/antibody ratio on macrophage uptake, processing, and presentation to T cells of antigen complexed with polyclonal antibodies.
Activation of a galactosidase-specific murine T hybridoma clone and of a human tetanus toxoid-specific T clone by antigen-presenting cells (APC) was used to evaluate the regulatory function of antibodies complexed with the relevant antigen. Complexed antigen, in fact, is taken up with high efficiency thanks to Fc receptors borne by APC. Antibody/antigen ratio in the complexes proved to be a critical parameter in enhancing antigen presentation. Complexes in moderate antibody excess provided optimal T cell activation independently of the physical state of the complexes (precipitated by a second antibody or solubilized by complement). Complexes in extreme antibody excess, on the contrary, did not yield T cell activation although taken up by APC efficiently. The effect of antibodies at extreme excess was observed with substimulatory dose of antigen (loss of potentiation) and with optimal dose of antigen (loss of stimulation). An excess of specific polyclonal antibodies hampers proteolytic degradation of antigen in vitro, supporting the view that a similar mechanism may operate within the APC that have internalized immune complexes in extreme antibody excess. The possibility that immune complex forming in extreme antibody excess may turn off the T cell response is proposed as a regulatory mechanism.
Animals↗
Limited clonal heterogeneity of antigen-specific T cells localizing in the pleural space during mycobacterial infection.
To detect possible differences in phenotype and fine specificity for mycobacterial antigens between CD4-positive T cells from peripheral blood (PB) and from inflammatory sites, we identified four patients presenting with a mycobacterial pleural exudate (PE) rich in PPD-specific lymphocytes and with a negative skin test to tuberculin purified protein derivative (PPD) and a negative proliferative response of PB lymphocytes to PPD at the same time. Several weeks after chemotherapy, these patients converted to PPD responsiveness in the periphery, and PPD-specific clones could be generated from PB at this stage. The phenotypic comparison of PE lymphocytes and concomitant PB lymphocytes obtained before treatment showed an increase of CD8 cells and a high frequency of HLA-DR-positive activated T cells in PE. The frequency of tetanus toxoid-specific and Candida albicans-specific proliferating T cells was lower than that of PPD-specific cells in PE but not in PB. PPD-specific clones were derived initially from PE and from PB once the patients had converted to PPD responsiveness. The two sets of clones from each patient were compared for proliferative response to mycobacterial antigen clusters of defined molecular weight ranges. A large number of PE-derived clones (36%) responded to a fraction of 27 to 35 kDa, whereas only one clone from PB responded to the same fraction. The purified antigen P32 (32 kDa), a soluble mycobacterial protein, stimulated PE-derived clones that were responsive to the 37- to 27-kDa fraction but did not stimulate PB-derived clones. The data demonstrate that PE- and PB-derived lymphocytes differ both in phenotype and in fine specificity, suggesting a limited clonal heterogeneity of T cells localizing at the inflammatory site in tuberculous patients without a PPD response in the periphery. Therefore T cells compartmentalized at inflammatory sites provide information that is different from that provided by T cells in the periphery.
Antigens, Bacterial↗
[Anti-HLA antibodies (Ab1) and anti-idiotypic antibodies (Ab2) directed against Anti-HLA Ab1 in various preparations of polyspecific immunoglobulins for intravenous use].
In this study, different intravenous immunoglobulin infusions (I.V. Ig.), were analyzed for the presence of either anti-HLA antibodies (Ab1) or anti-idiotypic antibodies (Ab2) directed against Ab1 anti-HLA. No evidence of either antibody types was found in tested I.V. Ig. preparations. Because of the absence of Ab1 anti-HLA, prophylactic and/or therapeutic use of I.V. Ig. appears safe in patients waiting for organ graft or in transplanted patients. The lack of Ab2 anti-Ab1 anti-HLA makes worthless the utilization of such preparations for neutralization of Ab1 present in highly sensitized dialysis patients or suppression of their production in transplanted patients in contrast with the previous reports suggesting this possibility.
Antibodies, Anti-Idiotypic↗
Limiting dilution analysis of alloreactive precursors is more discriminatory than MLR to evaluate functional histocompatibility.
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Cells, Cultured↗
Differential activation of T cell clones stimulated by macrophages exposed to antigen complexed with monoclonal antibodies. A possible influence of paratope specificity on the mode of antigen processing.
We have used the enhanced uptake by FcR-bearing cells observed when Ag is administered as an immune complex to investigate the possible impact of specific antibodies on processing and presentation of antigen by accessory cells. The Ag Escherichia coli beta-galactosidase alone or bound to different mAb was incubated with peritoneal macrophages. These were subsequently exposed to a battery of Ag-specific T hybridoma clones. The resulting production of IL-2 was taken as a measure of effective presentation. The results of 43 mAb-T clone combinations showed a potentiation of presentation of Ag at substimulatory concentration in the majority of the cases, indicating that each mAb is conducive to FcR-mediated uptake by macrophages, and that each T clone can be stimulated by properly presented Ag. In contrast, nine combinations yielded a lower response, two of them falling to baseline values. We attribute these results, which corroborate our previous evidence of directional help in the beta-galactosidase system, to a modulation in enzymatic processing of Ag and its subsequent presentation imposed by the paratope of the mAb binding to the relevant epitope.
Antibodies, Monoclonal↗
B cells on the podium: regulatory roles of surface and secreted immunoglobulins.
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Animals↗
Effect of cyclosporine on the antigen-presenting function of human and murine accessory cells.
Recent reports have challenged the belief that accessory cells are resistant to cyclosporine. Such a tenet was based on the observation that several functions of accessory cells, such as IL-1 production and phagocytosis, are resistant to the drug. On the other hand, when a less primitive, more refined function of accessory cells was examined--i.e., the capacity to take up, process, and present antigen in an MHC-restricted fashion to antigen-specific T lymphocytes, CsA proved to be an effective inhibitor. In contrast to this finding, when antigen was provided in the form of an immune complex prepared with a monoclonal antibody, uptake of antigen--likely mediated by the Fc receptors--and subsequent processing and presentation were not affected by CsA. These results suggest that, depending on whether the antigen is taken up by constitutive or by receptor-mediated endocytosis, accessory cells can be functionally defined as resistant or sensitive to CsA.
Animals↗
Cyclosporine sensitivity of human alloreactive T lymphocytes depends on the strength of the allogeneic stimulus.
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Cells, Cultured↗
The serum capacity to solubilize immune complexes (ICSC) measured by an enzyme-anti-enzyme complex probe.
The capacity to solubilize immune complexes can be readily measured by incubating the test serum with a suspension of an immune precipitate formed by beta-galactosidase and anti-beta-galactosidase antibody, and then reading the enzyme units (EU) liberated in the clear supernatant. Our method is rapid and inexpensive; it can be performed in plates and read in scanning colorimeters. Although on large numbers of observations the ICSC is significantly correlated with the CH50, a few discordant cases suggest that solubilization and haemolysis are functions of the alternative and classical pathways of complement respectively.
Antigen-Antibody Complex↗
Constraints in T-B cooperation related to epitope topology on E. coli beta-galactosidase. I. The fine specificity of T cells dictates the fine specificity of antibodies directed to conformation-dependent determinants.
Experiments to test the relationship between the epitopes on a protein antigen recognized by T and B cells in their collaboration to produce antibody cannot rely solely on hapten-carrier models. In the present work we used E. coli beta-galactosidase, a molecule whose tertiary and quaternary epitopes have been well characterized, as the model antigen. T helper cells were raised by stimulating mice with the intact or the denatured molecule or with any of several beta-galactosidase cyanogen bromide peptides. In a series of in vitro helper T cell assays we confronted the various T populations with B cells preimmunized with the native antigen, and we tested their capacity to help production of (a) binding antibodies and (b) antibodies directed to single conformational epitopes, characterized by their capacity to protect the enzyme from heat denaturation or to activate defective beta-galactosidase. According to our results, (a) equivalent T cell help can be provided by T helper cells primed with native or denatured antigen, even for the production of "conformational" antibodies; (b) one of the peptides (CB-18) is most efficient in raising help for binding antibodies; and (c) two peptides (CB-20 and CB-21) rank highest in priming T helper cells for the eventual production of protecting and activating antibodies, respectively. Thus, not every beta-galactosidase-specific T helper cell is useful in providing help to B cells specific for any particular epitope on the molecule, but rather preferential pairings exist, possibly governed by a proximity rule.
Animals↗
Handling of retroviral antigens by human antigen-presenting cells.
Antigen-specific T helper cells play an important role in retroviral infections. Indeed, they provide help for B-cell activation and antibody production and for clonal expansion of cytolytic lymphocytes. Therefore, we used retrovirus-specific human T helper clones in order to define modes of antigen presentation, antigen-presenting cells and the molecular context of Th epitopes that could be exploited in the design of immunogens aimed at optimizing the Th cell response. In particular, we describe several mechanisms of receptor-mediated antigen uptake that enhance the stimulation of human T-cell clones specific for HIV and HTLV-1 antigens; we report on the differential recognition of Th epitopes depending on the molecular-viral context; we show that dendritic cells are the most efficient presenting cells and are essential for the induction of in vitro primary Th cell responses; and finally, we propose that Th cells specific for internal, conserved antigens of HIV such as reverse transcriptase, may be candidates for intrastructural help resulting in induction of envelope specific antibodies.
Antigen Presentation↗