Differential effect of alpha-tocopherol and ascorbate on oxidative injury induced in immune cells by thermal stress

As immune cells are often subjected to hyperthermia that can easily occur either after intense and/or prolonged exercise or during defense against pathogens, in this paper we analysed whether superoxide anion production occurred in lymphocytes exposed to high temperature and, consequently, if antioxidants could exert any protective function. The results demonstrated that an increase of superoxide anion was induced in rabbit lymphocytes exposed to 42 degrees C for 1h, although cell viability was no affected. However, suppression of either Pokeweed mitogen (PWM)-driven cell proliferation, or immunoglobulin production or IL-2 synthesis was observed. To evaluate the capacity of antioxidants to restore the immune suppressed responses, two vitamins, alpha-tocopherol and ascorbic acid, were added to PWM-stimulated cultures following heat treatment. The data demonstrated that alpha-tocopherol was able to totally abrogate the inhibitory effects mediated by thermal stress, while ascorbic acid did not give any protective results.

Natural killer clones recognize specific soluble HLA class I molecules

Enhancement of major histocompatibility complex (MHC) class I expression leads to protection from natural killer (NK) cell recognition in several systems. MHC class I gene products are released from the cell surface and can be found in sera as soluble forms. To investigate the possible immunoregulatory role of soluble HLA (sHLA) in NK cell-target recognition, several sHLA antigens were studied for their ability to induce NK cell cytotoxicity modulation. NK cell-target recognition was inhibited by the addition of sHLA during the cytotoxicity assay. Our results indicate that sHLA molecules can down-regulate NK killing at the effector level. Moreover, different NK clones are able to specifically recognize different sHLA antigens. Kp43 molecules seem to be involved in the NK recognition of sHLA-B7.

Ligation of either CD2 or CD28 rescues CD4+ T cells from HIV-gp120-induced apoptosis

Temporal or quantitative imbalance in signals delivered to T cells via T cell antigen receptor (TCR), the CD4 co-receptor, and accessory molecules can lead to anergy, apoptosis, or both. This has been observed following ligation of CD4 by HIV gp120 prior to TCR occupancy. The ability of molecules such as CD2 and CD28, interacting with their ligands LFA-3 and B7, to provide signals that protect T cells from the induction of anergy, has been reported. Here, we demonstrate that ligation of CD2 and CD28 in conjunction with TCR occupancy rescue T cells that have been programmed for apoptotic death by prior CD4 ligation to gp120. This appears to be the result of augmented interleukin-2 and interleukin-4 release by the T cells following these molecular interactions. In conclusion, our results suggest that an impairment of antigen-presenting accessory cell functions could favor gp120-mediated apoptosis in HIV-uninfected cells.

Differential susceptibility to monomeric HIV gp120-mediated apoptosis in antigen-activated CD4+ T cell populations

To support the hypothesis that indirect mechanisms mediated by viral products like the HIV envelope glycoprotein gp120 could be responsible for T lymphocyte depletion in HIV infection, we developed a system in which the impairment of T cell functions could be investigated in vitro. In particular, we characterized the conditions that allow T lymphocytes repeatedly stimulated with an antigen to be sensitive or resistant to gp120-mediated apoptotic signals. To achieve this goal, a panel of antigen-specific CD4+ T cell clones and primary CD4+ T lymphocytes were treated for 2 and 18 h with saturating amounts of monomeric gp120 (without cross-linking with specific antibodies) and antigen-driven T cell proliferation and apoptosis were analyzed. We show that monomeric gp120 induces apoptosis only in T lymphocytes repeatedly stimulated with the antigen, that primary T lymphocytes are resistant to programmed cell death mediated by monomeric gp120, but are sensitive to anti-CD4 antibodies, and that gp120-mediated apoptosis is dependent on the period of time between the binding of gp120 to CD4 and the encounter with antigen. To investigate the different susceptibility to gp120 induced apoptosis of primary CD4+ and T cell clones further, the number of membrane CD4 molecules and their affinity for gp120, together with Bcl-2 and Fas expression, were studied. Our data suggest that a down-modulation of membrane CD4 together with high expression of the Bcl-2 gene and protein characterizes the susceptibility to apoptosis of gp120-treated cells. In conclusion, our results define the phenotypic features of T cells susceptible to HIV gp120-induced apoptosis and demonstrate that the same clonotype, depending on the activation state, may present a differential sensitivity to apoptosis induction.

Identification of a novel HLA-B27 subtype by restriction analysis of a cytotoxic gamma delta T cell clone

Seven HLA-B27 alleles are known, which share the same allospecificity, but differ by one to six amino acid substitutions. Herein, we describe a novel HLA-B27 allele, provisionally named B27-ci, which is expressed by an individual from whom a B27-restricted gamma delta T cell clone has been derived. This clone recognizes B cell lines from the proband and all of the other B27-positive members of the family, but does not lyse B cell lines that express other HLA-B27 alleles. The amino acid sequence deduced from three B27-ci cDNA clones was found to differ from the B*2705 sequence by one amino acid substitution (Asp to His) in position 116 of the alpha 2 domain. This position has been shown to lie in the floor of the F pocket, where it plays a key role in determining the nature of the amino acid side chain that will fit into this pocket. Moreover, the fact that the clone described here possesses a TCR-gamma delta indicates that this subset of cells not only can be HLA-restricted, but also can finely discriminate among classical class I molecules.

Identification of a novel HLA-B27 subtype by restriction analysis of a cytotoxic gamma delta T cell clone

Seven HLA-B27 alleles are known, which share the same allospecificity, but differ by one to six amino acid substitutions. Herein, we describe a novel HLA-B27 allele, provisionally named B27-ci, which is expressed by an individual from whom a B27-restricted gamma delta T cell clone has been derived. This clone recognizes B cell lines from the proband and all of the other B27-positive members of the family, but does not lyse B cell lines that express other HLA-B27 alleles. The amino acid sequence deduced from three B27-ci cDNA clones was found to differ from the B*2705 sequence by one amino acid substitution (Asp to His) in position 116 of the alpha 2 domain. This position has been shown to lie in the floor of the F pocket, where it plays a key role in determining the nature of the amino acid side chain that will fit into this pocket. Moreover, the fact that the clone described here possesses a TCR-gamma delta indicates that this subset of cells not only can be HLA-restricted, but also can finely discriminate among classical class I molecules.

Different regions of the N-terminal domains of HLA-DR1 influence recognition of individual peptide-DR1 complexes

The contributions of individual amino acids in the polymorphic beta chain and the conserved alpha chain of HLA-DR1 to influenza HA-specific DR1-restricted and anti-DR1 allospecific T-cell recognition were analyzed. The genes encoding HLA-DR1 were subjected to site-directed mutagenesis in order to introduce single amino acid substitutions at 12 positions in the beta 1 domain and 11 positions in the alpha 1 domain. The beta 1-domain substitutions were all at polymorphic positions and introduced residues that are found in DR4 alleles. The amino acids introduced into the DR alpha 1 domain were based on the sequences of other human and mouse class II alpha chains. The responses of 12 DR1-restricted T-cell clones specific for two peptides of HA and seven anti-DR1 allospecific clones were studied. Substitutions at positions that point up from and into the peptide-binding site in the third variable region of the beta 1-domain alpha-helix caused substantial reduction in the responses of all of the clones. Substitutions at multiple positions in the beta 1-domain floor and in the alpha 1 domain influenced the anti-DR1 responses of the alloreactive and of the HA100-115-specific T-cell clones. In contrast, very few changes outside of the beta 1 domain third variable region affected the responses of the HA306-324-specific DR1-restricted T-cell clones. These results suggest that a surprisingly limited region of the HLA-DR1 molecule is critically involved in T-cell recognition of HA306-324 by DR1-restricted T cells. However, the susceptibility of the HA100-115-specific and the anti-DR1 allospecific T-cell clones to substitutions at multiple positions in both N-terminal domains shows that the response to DR1-HA306-324 is unusual and may reflect the promiscuity with which this peptide binds to HLA-DR molecules.

Analysis of susceptibility of mature human T lymphocytes to dexamethasone-induced apoptosis

We present evidence that dexamethasone (Dex), a synthetic glucocorticosteroid, causes apoptosis in mature human T cells, similarly to what has been reported for murine T lymphocytes. Human T cell clones and short-term activated T lymphocytes treated with Dex show the characteristic pattern of apoptotic cells, such as hypodiploid nuclei, chromatin condensation and DNA fragmentation into oligonucleosomal fragments. However, Dex susceptibility of T cells to apoptosis is cell cycle-dependent. The progression in the proliferative cell cycle (G1 versus S) rescues Dex-treated T cells from apoptosis. Moreover, occupancy of the T cell receptor reverses Dex-induced apoptotic phenomena. These observations suggest that glucocorticoids contribute to the regulation of the proliferative or the suicidal response of antigen-activated human T cells.

Dexamethasone-dependent modulation of human lymphoblastoid B cell line through sphingosine production

The relationship between dexamethasone-dependent changes in intracellular sphingosine levels, energy and phospholipid metabolism have been investigated by 31P-NMR spectroscopy and high-performance liquid chromatography. The cellular functions have been evaluated by cellular growth and immunoglobulin M secretion (IgM). Significant increases in intracellular phosphorylcholine (PCho), extracellular choline (Cho), and endogenous sphingosine levels were observed only at 30 min incubation with dexamethasone. These results confirmed a sphingosine-dependent hydrolysis of choline-linked phospholipids (Miccheli, A., Ricciolini, R., Piccolella, E., Delfini, M. and Conti, F. (1991) Biochim. Biophys. Acta 1093, 29-35). Furthermore, no significant variations were evidenced at hours 1, 2, 6 and 18 of incubation. Dexamethasone causes an inhibition of cellular growth and IgM secretion as well as the sphingosine treatment. The results suggest that the effect of dexamethasone may be mediated by endogenous sphingosine production in Epstein-Barr virus transformed B lymphocytes.

Dexamethasone-dependent modulation of cholesterol levels in human lymphoblastoid B cell line through sphingosine production

The effect of dexamethasone on lipid composition of Epstein-Barr virus transformed human B lymphocytes have been investigated by 31P- and 1H-NMR spectroscopy and compared to the effects due to exogenous sphingosine treatment. Furthermore, the effects of dexamethasone and sphingosine on membrane structure was evaluated by fluorimetry. No significant changes were evidenced in phospholipid composition and in the ratio of unsaturated to total fatty-acid chains. A significant increase in total cholesterol levels was evident at 30 min incubation with dexamethasone or sphingosine; a parallel increase in DPH polarization at 30 min was also demonstrated. TMA-DPH intensity measurements suggest a slowing of vesicular intracellular traffic due to the treatment. The results suggest a dexamethasone- and sphingosine-dependent inhibition of intracellular cholesterol transport.

Characterization of an IS-like element from Mycobacterium tuberculosis

A DNA sequence, present in members of the Mycobacterium tuberculosis complex, has been identified and characterized. The distribution of this DNA sequence among mycobacterial species was analysed by DNA hybridization and PCR experiments. As the sequence was detected only in bacteria belonging to the M. tuberculosis complex, it may be useful for the rapid discrimination of mycobacteria. Interestingly, the sequence has some characteristics of an insertion element (IS) and codes for a hypothetical protein with significant homologies to proteins encoded by several IS elements of other organisms, namely IS427 and IS869 from Agrobacterium tumefaciens, IS402 from Pseudomonas cepacia, Tn4811 from Streptomyces lividans and ISRm4 from Rhizobium meliloti. Together, these elements form a previously unrecognized family of transposable elements. This finding suggests the possibility of horizontal gene transfer between pathogenic mycobacteria and other organisms including Gram-negative plant-pathogenic bacteria.

Antibody repertoire against the A60 antigen complex during the course of pulmonary tuberculosis

The A60 antigen complex is a Mycobacterium bovis (BCG) highly immunodominant antigen containing both B and T-cell epitopes. Clinical-serological studies show that elevated anti-A60 titres are present during tuberculosis. We wished to analyze in detail antibody responses against A60 components during the course of tuberculosis. A mixed longitudinal study was designed including individuals at the onset of tuberculosis, during treatment and after resolution of the disease. The anti-A60 repertoire was analyzed using a western blot assay with A60 as the antigen. While PPD- normals recognized only the 65 kDa heat shock protein (HSP), PPD+ normal individuals displayed low levels of anti-A60 antibodies against dominant antigens. There were immunoglobulin M (IgM) and immunoglobulin G (IgG) consistent with response to a latent infection. Onset tuberculosis was characterized by IgM and IgG antibodies against 52 to 28 kDa antigens; IgM response being limited to earlier phases of the disease. In contrast, IgM antibodies against 25 to 14 kDa antigens appeared only 2-6 months after disease onset. The antibody repertoire of chemotherapy-treated, resolved tuberculosis was exclusively IgG in isotype, as for a memory-type response. Thus, western blot analysis with A60 identifies typical antibody patterns associated with different clinical phases of tuberculosis infection. Such approach may help in identifying new single antigens for serologic diagnosis of active tuberculosis.

Antibody repertoire against the A60 antigen complex during the course of pulmonary tuberculosis

The A60 antigen complex is a Mycobacterium bovis (BCG) highly immunodominant antigen containing both B and T-cell epitopes. Clinical-serological studies show that elevated anti-A60 titres are present during tuberculosis. We wished to analyze in detail antibody responses against A60 components during the course of tuberculosis. A mixed longitudinal study was designed including individuals at the onset of tuberculosis, during treatment and after resolution of the disease. The anti-A60 repertoire was analyzed using a western blot assay with A60 as the antigen. While PPD- normals recognized only the 65 kDa heat shock protein (HSP), PPD+ normal individuals displayed low levels of anti-A60 antibodies against dominant antigens. There were immunoglobulin M (IgM) and immunoglobulin G (IgG) consistent with response to a latent infection. Onset tuberculosis was characterized by IgM and IgG antibodies against 52 to 28 kDa antigens; IgM response being limited to earlier phases of the disease. In contrast, IgM antibodies against 25 to 14 kDa antigens appeared only 2-6 months after disease onset. The antibody repertoire of chemotherapy-treated, resolved tuberculosis was exclusively IgG in isotype, as for a memory-type response. Thus, western blot analysis with A60 identifies typical antibody patterns associated with different clinical phases of tuberculosis infection. Such approach may help in identifying new single antigens for serologic diagnosis of active tuberculosis.

Subtelomeric as well as telomeric sequences are lost from chromosomes in proliferating B lymphocytes

B lymphocytes purified from peripheral blood can be normally cultured in vitro for only one doubling. They can undergo an unlimited number of cell divisions after transformation with a DNA tumor virus such as the Epstein-Barr virus. We have shown that the terminal restriction fragments of virus transformed B lymphocytes are shortened in the course of proliferation and that this process is accompanied by structural modifications. We have identified the sequences that are lost during the shortening process by hybridization to the canonical human telomeric simple repeat TTAGGG, to other simple sequences that are found at the ends of human chromosomes, and to a human subtelomeric sequence. We have observed that by 20 doublings over half the TTAGGG sequences, but few or no TGAGGG sequences, are lost from the TRFs. The subtelomeric sequence was removed from most of the TRFs on which it was present. The implications that these observations have on the problems of cell senescence and oncology are discussed.

Mycobacterial antigen complex A60-specific T-cell repertoire during the course of pulmonary tuberculosis

The Mycobacterium bovis antigen complex A60 is known to be immunodominant in tuberculosis and to have a protective effect against experimental infection in vitro and in vivo. To identify immunodominant and possibly protective antigens in pulmonary tuberculosis, the T-cell repertoire directed to nitrocellulose-bound fractions of A60 antigen was analyzed in active tuberculosis patients during the course of the infection and after recovery. The results show that patients infected with Mycobacterium tuberculosis acquired complete A60-T-cell reactivity only in the late phases of infection. At disease onset, patients with active tuberculosis were characterized by (i) T-cell unresponsiveness to most A60 fractions, (ii) high tumor necrosis factor alpha production, and (iii) low gamma interferon (IFN-gamma) release. Several weeks after chemotherapy, the unresponsive state disappeared and the following reverse situation was observed: (i) high blastogenic response to almost all A60 fractions, (ii) low tumor necrosis factor alpha release, and (iii) high IFN-gamma production. In addition, 60% of these patients significantly responded against seven A60 fractions (61 to 58, 56 to 53, 49 to 46, 46 to 44, 35 to 33, 33 to 30, and 30 to 28 kDa), indicating that they included immunodominant antigens. Furthermore, only the fractions within the molecular mass ranges of 56 to 44 and 35 to 28 kDa induced IFN-gamma synthesis. One year after complete recovery from infection, more than 60% of past-active tuberculosis subjects had memory T cells specific for the immunodominant fractions of 61 to 58, 56 to 53, 49 to 46, and 33 to 30 kDa. Since the same fractions induced the strongest IFN-gamma production, known to exhibit antimycobacterial effects, it is suggested that these may represent the inducers of a protective immune response.

A new tripeptide, Pol 509, influences biochemical events associated with antigen presentation efficiency of PPD-specific EBV-B cells

A synthetic tripeptide (pGLU-LEU-TRP-OCH3) Pol 509, derived from snake venom, was studied directly by analyzing the interactions with synthetic lipid bilayers using NMR spectroscopy. Functional studies were also performed by measuring the effects: i), on early biochemical events (adenyl cyclase and phospholipase C activation products), intermediate (surface Ag expression) and late (DNA synthesis) parameters following B-cell activation elicited by PPD-linkage to specific membrane Ig; and ii), on the presentation of PPD to Ag-specific T-cell lines. Comparative experiments using PMA and IFN-gamma were also performed. We found that all parameters studied were affected by Pol 509 treatment. In fact, while PPD linkage to mlg reversed the balance between cAMP and IP3 existing in unstimulated EBV-B cells, Pol 509 reduced the PPD-induced accumulation of cAMP to control values and induced a further decrease of IP3 level. Pol 509-mediated decrease of these second messenger levels was accompanied by a slight increase of HLA-DR molecule expression and DNA synthesis inhibition. Furthermore, Pol 509 enhanced the efficiency of PPD presentation to T-cell lines. Taken together, these observations suggest that Pol 509, which enhances Ag presentation by modifying second messenger levels, may be considered as a new immunomodulatory drug with immunopotentiating activity.

Modulation of the free sphingosine levels in Epstein Barr virus transformed human B lymphocytes by phorbol dibutyrate

The amounts of free sphingosine in Epstein Barr virus transformed B lymphocytes (EBV-B) treated with sphingosine and phorbol-12,13-dibutyrate (PD) has been quantified by high performance liquid chromatography (HPLC). PD treatment did not affect intracellular sphingosine level, while it seems to lessen the removal of this long chain base in sphingosine-treated EBV-B cells. The previous results relative to sphingosine-dependent changes in choline-metabolite levels have to be interpreted on the basis of these results.

Modulation of human lymphoblastoid B cell line by phorbol ester and sphingosine. A 31P-NMR study

Changes in phospholipid and energy metabolism in Epstein-Barr Virus transformed B lymphocytes (EBV-B), induced by phorbol 12,13-dibutyrate (PD) and sphingosine (an inhibitor of protein kinase C), have been evaluated by 31P-NMR spectroscopy. The effects of PD and sphingosine on [3H]thymidine incorporation have also been studied. An increase in phosphorylcholine (PCho) levels has been observed in sphingosine and sphingosine + PD treated cells after 30 min of incubation, whereas no change was observed in lymphocytes incubated with PD during the same period. Extracellular choline levels increased in sphingosine treated cells but decreased in PD treated cells. Hence, a sphingosine-dependent hydrolysis of choline-linked phospholipids is suggested. A time-dependent reduction of PCho observed after 120 min PD incubation is consistent with an increase of the synthesis of choline-linked phospholipids.

Regulation of self-major histocompatibility complex reactive human T-cell clones

The proliferative response of human T-lymphocyte clones, (TLC) specific for self-major histocompatibility complex (MHC) products either alone or associated with PPD epitopes are inhibited in vitro by dexamethasone (DEX) and by a non-specific inhibitory factor(s) (nsINH) produced by PPD-activated T-cells. The inhibiting effect has been investigated by preincubating autoreactive and PPD-specific TLC with nsINH or DEX. Results obtained indicate that T-lymphocytes are the target of these two immunoregulatory molecules. Moreover, the addition of exogenous recombinant interleukin 2 (rIL-2) substantially reverses the inhibition observed in both nsINH- or DEX-treated cultures.

Identification of a 35-kilodalton Mycobacterium tuberculosis protein containing B- and T-cell epitopes

Screening of a Mycobacterium tuberculosis genomic DNA library in the lambda gt11 expression vector was carried out by using, as probes, sera from tuberculous patients and murine monoclonal antibody H61.3 recognizing a mycobacterial 35-kilodalton protein present only on the M. tuberculosis complex. The recombinant beta-galactosidase-fused protein present in the crude lysate induced the proliferation of T lymphocytes from patients with tuberculous pleuritis. As the recombinant insert contains an internal EcoRI restriction site, it was possible to identify two fragments, one proximal to the lacZ gene and 1.7 kilobases (kb) in size and the other distal to the lacZ gene and 2.2 kb in size. Southern blot analysis showed that both of them hybridized with the genomic DNA from M. tuberculosis and M. bovis but not with the DNA from other mycobacterial species. To perform extensive immunological studies, the amount of beta-galactosidase-fused protein being very low, we fused the 1.7-kb fragment to the N-terminal part of the gene coding for the DNA polymerase of bacteriophage MS2 in the expression vector pEx34. The fusion protein was partially purified, and subsequent Western blotting (immunoblotting) and T-cell proliferation experiments confirmed the presence of B- and T-cell mycobacterial epitopes. Furthermore, to isolate the chromosomal region containing the 35-kilodalton gene, we constructed another mycobacterial genomic library in the lambda 2001 vector by cloning 15 to 20 kb of foreign DNA. Screening of this library was carried out by using 1.7- and 2.2-kb recombinant fragments as probes. Restriction maps of some clones isolated were determined.

Increased autoreactive T cell frequency in tuberculous patients

The development of putative self-MHC-reactive T cells and their precursor frequency was estimated in peripheral blood lymphocyte cultures stimulated in vitro with PPD. The role of foreign antigen in the generation of self-MHC-reactive T cells in vivo was analyzed by comparing the frequency of autoreactive T cells in the peripheral blood of tuberculous patients with that observed in healthy individuals. It was found that PPD in vitro and Mycobacterium tuberculosis infection in vivo increased substantially the generation of autoreactive T cells. Autoreactive T cell clones were shown (1) to recognize self MHC class II products; (2) to release gamma interferon in the absence of exogenous antigen, and (3) to express autocytotoxic activity. All these findings suggest that self-MHC-reactive T cells may be involved in the inflammatory response to M. tuberculosis.

Limiting dilution analysis of T cell unresponsiveness to mycobacteria in advanced disseminated tuberculosis

Peripheral blood mononuclear cells from patients with advanced disseminated tuberculosis (Dis-TB) do not respond to purified protein derivative (PPD) measured as cell proliferation, lymphokine production and interleukin (IL)-2 receptor (Tac antigen) expression. Limiting dilution analysis revealed "multi-hit" curves and low frequencies of PPD-reactive T cells in cultures of Dis-TB, and "single-hit" curves and high frequencies of PPD-reactive T cells in cultures of patients with localized form of pulmonary tuberculosis. Moreover, a strict relationship between Tac antigen expression and ability of exogenous IL-2 to enhance bulk culture cell proliferation was observed in Dis-TB patients.

Epstein-Barr virus-transformed B cells process and present Mycobacterium tuberculosis particulate antigens to T-cell clones

We have analyzed the presentation of mycobacterial antigens by Epstein-Barr virus-transformed human B (EBV-B) cells to mycobacteria-specific T-cell clones and lines, and to purified resting T cells. EBV-B cells were able to process and present not only soluble forms of antigen, such as PPD and the expressate preparation of M. tuberculosis strain H37Rv, but also particulate forms of antigen, such as whole mycobacterial H37Rv or M. bovis organisms. Electron microscopy studies demonstrated the capacity of EBV-B cells to phagocytose mycobacterial cells in 18 hr and pulsing experiments confirmed that an 18-hr of incubation is required for an efficient processing and presentation of mycobacterial determinants to T cells. The processing of whole-H37Rv particulate antigen by EBV-B cells was inhibited by the lysosomotrophic compound chloroquine and by high doses of irradiation. Finally, the analysis of the presentation of soluble and particulate mycobacterial antigens by PPD-positive and PPD-negative EBV-B cell clones has shown a preferential presentation of both forms of antigen by PPD-positive EBV-B clones.

Immunology of tuberculosis: new directions in research

Tuberculosis is still one of the major health problems in almost all over the world. Thus, new directions in basic and applied research on tuberculosis are under investigation. In this review we have provided recent data obtained in our laboratories on three main aspects of the immunology of tuberculosis, namely: i. the role of B lymphocytes in the processing and presentation of Mycobacterium tuberculosis antigens to T cells; ii. the activation and characterization of mycobacterial-specific T cell clones; iii. the T cell regulation of the immune response to M. tuberculosis. The analysis of the antigenic determinants of M. tuberculosis relevant in the antimycobacterial immunity is the major goal of the WHO programme on the immunology of tuberculosis. In fact, the attempt to develop a second generation vaccine against this microorganism is now possible by analyzing recombinant genomic DNA libraries of M. tuberculosis with monoclonal antibodies and T cell clones. In the near future, the identification of epitopes recognized by mycobacterial-specific T cells with helper, cytotoxic and suppressor functions will allow the preparation of recombinant and synthetic vaccines effective in the control of this disease.

Regulation of immune interferon production during the response to soluble microbial antigens

Human peripheral blood mononuclear cells (PBMC) stimulated in vitro with purified protein derivative (PPD) or with a Candida albicans polysaccharide extract (MPPS) released immune interferon (IFN) and interleukin 2 (IL-2). Kinetic studies showed a biphasic production of IFN with maximum levels at days 3-4 and days 5-6 of culture. In contrast, the IL-2 production is only observed at days 2-3 of culture. The relationship between IFN and IL-2, analysed both in responder and nonresponder PBMC cultures, showed that the early peak of IFN production appears to be IL-2 independent whereas the second peak seems strictly related to the presence of IL-2 culture. Furthermore, monoclonal antibodies against class I and class II products of the major histocompatibility complex (MHC) inhibited IFN production when added at the beginning of culture, whereas only anti-class I antibodies interfered with the release of IFN when added to antigen-primed lymphocytes.