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Biomedical subjects

F Manca

Publications and source records attributed to F Manca.

At least 73 records · Page 4Linked to original sources
PubMed1991

The naive repertoire of human T helper cells specific for gp120, the envelope glycoprotein of HIV.

The envelope glycoprotein of HIV gp120 is a T cell Ag in experimental animals and in humans infected with HIV or deliberately immunized with gp120 in various forms. Inasmuch as T cell responses result from the interaction of Ag processed and presented by APC with the unprimed T cell repertoire, we have investigated the human T cell repertoire specific for gp120 in seronegative, normal individuals. T cell lines and clones specific for HIV gp120 were generated by repeated in vitro stimulation of peripheral blood T lymphocytes with gp120-pulsed APC, followed by IL-2 expansion. We observed that the T cell response to whole gp120 involved single restricted immunodominant epitopes in gp120 that differ between responding individuals. Focusing of the response to limited regions of gp120 when the whole Ag is used for priming suggests that one or more adjacent epitopes are immunodominant and mask responses to "immunorecessive" epitopes. We have been able to generate primary in vitro responses to recessive epitopes by stimulation in vitro with synthetic peptides of gp120. The results indicate that a much broader T repertoire can be detected when individual peptides are used for priming in vitro rather than gp120. This information has important implications for the development of vaccination protocols aimed at eliciting diverse immune responses to "immunorecessive" regions of envelope glycoprotein.

Epitopes↗
PubMed1991

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↗
PubMed1991

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↗
PubMed1991

Interference of monoclonal antibodies with proteolysis of antigens in cellular and in acellular systems.

Monoclonal antibodies complexed with protein antigens can interfere with proteolytic degradation of the antigen. Depending on their fine specificity, they can "protect" well defined regions of the antigen. Because of steric hindrance between bound antibody and proteolytic enzyme, the protected region is larger than the minimal epitope recognized by the antibody binding site. The principle of limited proteolysis proves a valuable tool for the analysis of antigenic fragments and for epitope mapping. Since proteolysis of antigen also occurs in antigen presenting cells, degradation of antigen complexed with a monoclonal antibody (either taken up as an immunocomplex by Fc receptors, or taken up in complexed form with a surface immunoglobulin of a specific B cell) likely modulates the processing pattern of the antigen. This results in a different spectrum of peptides displayed by the antigen presenting cell and thus in different interactions with the antigen specific T cell repertoire. Modulation of T cell response and B cell response by using antigen complexed with different monoclonals is proposed as possible means of interfering with the fine specificity of the response.

Antibodies, Monoclonal↗
PubMed1990

HIV envelope glycoprotein, antigen specific T-cell responses, and soluble CD4.

Specific T cells stimulated by antigen presenting cells (APC) pulsed with antigen in the presence of HIV were no longer detectable with a functional assay, which suggests that HIV has been transferred from APC to the specific activated T cell via an antigen-dependent mechanism to exert its cytopathic effect on activated T cells. In contrast soluble gp120 inhibited antigen-driven proliferation, but this action was reversible and could be blocked by soluble CD4. Thus the chief mechanism of HIV pathogenesis may be gp120/CD4 interaction and HIV may be pathogenic mainly as a producer of gp120.

Antibodies, Monoclonal↗
PubMed1990

AIDS pathogenesis: HIV envelope and its interaction with cell proteins.

The immune deficiency induced by HIV has its origin in the interaction of the outer envelope glycoprotein gp120/gp41 with receptors present on human immunocytes. Virus binding to cells, virus entry and subsequent compartmentalization resulting in productive infection depends on the interaction of gp120/gp41 with CD4 and other accessory molecules. Gp120 and HIV are markedly immunosuppressive of T-cell responses and, in addition, HIV can functionally delete antigen responsiveness of T cells. Abolition of CD4 binding, by denaturation of gp120, allows study of T-cell epitopes in gp120 and shows the denatured molecule is highly immunogenic even in naive subjects (F. Manca, unpublished). The gp120-binding site of CD4 is shared with MHC class II molecules and the reaction of antibodies within this region of CD4 induces conformational changes that may be significant for virus entry into cells or for syncytial formation. The HIV envelope contains sites of sequence homology with monomorphic human MHC class II sites that do not appear to be naturally immunogenic in humans. In addition to the properties of gp120, it is hypothesized that HIV envelope may also represent an 'alloepitope' of class II to the human T-cell repertoire, and is therefore able to induce a chronic allogeneic response not dissimilar to experimentally induced GVHD. These features are of potential importance both for primary vaccination against HIV, and for the long-term treatment of HIV seropositive patients. Induction of effective T-cell responses to gp120 require use of a denatured or otherwise modified product lacking CD4-binding capacity. The potential distortion of the TCR repertoire by the class-II-homologous and CD4-interactive sequences must be assessed.(ABSTRACT TRUNCATED AT 250 WORDS)

Acquired Immunodeficiency Syndrome↗
PubMed1989

In vitro evidence for impaired cellular immune responsiveness in children with chronic renal failure.

We used mixed lymphocyte culture (MLC) as an assay to evaluate in vitro the cellular immune functions of children with chronic renal insufficiency (CRI) or with chronic renal failure (CRF). The proliferative response of lymphocytes from both groups of patients was significantly reduced as compared to the response of control individuals. In addition, the proliferative response of CRF patients treated with hemodialysis was significantly lower than the response of continuous ambulatorial peritoneal dialysis (CAPD) patients. These data confirm that a marked depression of the cellular immune response is detectable in a pediatric population, as predicted from data from the literature on the adult renal failure population.

Child↗
PubMed1989

Analysis of cellular populations in peritoneal effluents of children on CAPD.

The characterization of cellular populations in peritoneal effluents (PE) of CAPD patients has been the subject of few studies. In order to establish a possible correlation between PE cells and clinical parameters, we studied the immunocompetent cells that are found in uncomplicated patients. In this study we used cytofluorimetric analysis to characterize phenotypically immunocompetent PE cells. We studied 17 children with a mean age of 8.7 +/- 5.3 years, who had been on CAPD for a mean duration of 16 months. The patients never suffered from peritonitis. The effluents were collected after overnight dialysis and centrifuged to concentrate cells. Surface phenotype of PE cells was tested with a panel of monoclonal antibodies. The analysis of 40 PE samples showed that the various cell types were present with different frequencies, suggesting that a dominant phenotype cannot be defined. The ratio between M3 positive cells (monocytic-macrophagic lineage) and T3 positive cells (T lymphocytes) showed a tendency to decrease after initiation of CAPD. T4/T8 ratio in all samples did not differ from that of peripheral lymphocytes. A high frequency of activated T cells (41% +/- 13), defined by the presence of DR antigens on T3+ M3- cells, was seen in PE and confirmed by the high frequency of T cells expressing the IL-2 receptor.

Adolescent↗
PubMed1988

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↗
PubMed1988

Detection of parasite related antigens associated with conglutinin binding immune complexes in patients with Schistosoma haematobium.

An ELISA assay was designed to detect the presence of parasite related antigens associated with circulating immune complexes in patients affected by urinary schistosomiasis. The assay makes use of bovine conglutinin as the immune complex recognition unit and of human anti-Schistosoma antibody as the antigen recognition unit. Using this method we showed that 10 of 15 (67%) patients with a positive polyethylene glycol assay had circulating immune complexes in which parasite antigens could be detected.

Antigen-Antibody Complex↗
PubMed1988

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↗