Inhibition of B-cell function by concanavalin-A-induced suppressor cells

The in vitro immune response of normal spleen cells to the thymus-independent antigen dinitrophenylated levan (DNP-LE) was found to be inhibited by suppressor cells induced previously by concanavalin A (Con A) in vitro. At various suppressor to target cell ratios, the level of suppression observed was comparable to that seen in anti-sheep erythrocyte (SRBC) responses. Consequently, it is suggested that B cells constitute a direct target for Con-A-induced suppressor cell activity.

Intranasal IFNgamma extends passive IgA antibody protection of mice against Mycobacterium tuberculosis lung infection

Intranasal inoculation of mice with monoclonal IgA against the alpha-crystallin (acr1) antigen can diminish the tuberculous infection in the lungs. As this effect has been observed only over a short-term, we investigated if it could be extended by inoculation of IFNgamma 3 days before infection, and further co-inoculations with IgA, at 2 h before and 2 and 7 days after aerosol infection with Mycobacterium tuberculosis H37Rv. This treatment reduced the lung infection at 4 weeks more than either IgA or IFNgamma alone (i.e. 17-fold, from 4.2 x 10(7) to 2.5 x 10(6) CFU, P = 0.006), accompanied also by lower granulomatous infiltration of the lungs. IFNgamma added prior to infection of mouse peritoneal macrophages with IgA-opsonized bacilli resulted in a synergistic increase of nitric oxide and TNFalpha production and a 2-3 fold decrease in bacterial counts. Our improved results suggest, that combined treatment with IFNgamma and IgA could be developed towards prophylactic treatment of AIDS patients, or as an adjunct to chemotherapy.

Intranasal bacille Calmette-Guerin (BCG) vaccine dosage needs balancing between protection and lung pathology

Intranasal vaccination may offer practical benefits and better protection against respiratory infections, including tuberculosis. In this paper, we investigated the persistence of the Mycobacterium bovis-strain bacille Calmette-Guerin (BCG) Pasteur, lung granuloma formation and protection against pathogenic tuberculous challenge in mice. A pronounced BCG dose-dependent granulomatous infiltration of the lungs was observed following intranasal, but not after subcutaneous, vaccination. Corresponding doses of BCG, over a 100-fold range, imparted similar protection against H37Rv challenge when comparing the intranasal and subcutaneous vaccination routes. Interestingly, a BCG dose-dependent reduction of the H37Rv challenge infection was observed in the lungs, but not in the spleens, following both intranasal and subcutaneous vaccination. In the light of the observed concurrence between the extent of granuloma formation and the level of protection of the lungs, we conclude that intranasal vaccination leading to best protective efficacy needs to be balanced with an acceptable safety margin avoiding undue pathology in the lungs.

Time course of mycobacterial infection of dendritic cells in the lungs of intranasally infected mice

SETTING

Dendritic cells (DC) could regulate between the protective and pathogenic immune responses following tuberculous infection. In this paper we investigated if their early infection in the lungs represents a plausible alternative to cross-priming with mycobacterial antigens acquired from infected macrophages.

OBJECTIVE

To determine the extent and time course of infection of lung DCs following intranasal inoculation of BALB/c mice with green fluorescent protein (GFP) tagged Bacillus Calmette-Guerin (BCG).

RESULTS

A fraction of GFP-BCG infected lung cells were classified as monocytic DCs with the CD11c+IA+33D1+CD8a- phenotype. These cells represented 5-18% of the total GFP+ cells, the bulk of which were macrophages. The infected DCs could be separated by cell size into two fractions with similar cell surface staining properties during the 2-72 h period after infection. An unexpected difference was observed for the time course of infection between DCs and macrophages: DC infection peaked at 48 h followed by decline at 72 h, while the proportion of infected macrophages remained steady during the same period.

CONCLUSION

The presented results are direct evidence that monocytic DCs are recruited to the lungs and take up live bacilli within 48 h of intranasal infection with GFP-BCG. This finding is pertinent for the regulation of pulmonary and systemic immune responses and possibly for the dissemination of mycobacterial infection by DCs.

Cytokine profile, HLA restriction and TCR sequence analysis of human CD4+ T clones specific for an immunodominant epitope of Mycobacterium tuberculosis 16-kDa protein

The identification of immunodominant and universal mycobacterial peptides could be applied to vaccine design and have an employment as diagnostic reagents. In this paper we have investigated the fine specificity, clonal composition and HLA class II restriction of CD4+ T cell clones specific for an immunodominant epitope spanning amino acids 91-110 of the 16-kDa protein of Mycobacterium tuberculosis. Twenty-one of the tested 28 clones had a Th1 profile, while seven clones had a Th0 profile. None of the clones had a Th2 profile. While the TCR AV gene usage of the clones was heterogeneous, a dominant TCR BV2 gene family was used by 18 of the 28 clones. The CDR3 regions of BV2+ T cell clones showed variation in lengths, but a putative common motif R-L/V-G/S-Y/W-E/D was detected in 13 of the 18 clones. Moreover, the last two to three residues of the putative CDR3 loops, encoded by conserved BJ sequences, could also play a role in peptide recognition. Antibody blockade and fine restriction analysis using HLA-DR homozygous antigen-presenting cells established that 16 of 18 BV2+ peptide-specific clones were DR restricted and two clones were DR-DQ and DR-DP restricted. Additionally, five of the 18 TCRBV2+ clones recognized peptide 91-110 in association with both parental and diverse HLA-DR molecules, indicating their promiscuous recognition pattern. The ability of peptide 91-110 to bind a wide range of HLA-DR molecules, and to stimulate a Th1-type interferon (IFN)-gamma response more readily, encourage the use of this peptide as a subunit vaccine component.

The humoral response in TCR alpha-/- mice. Can gammadelta-T cells support the humoral immune response?

An optimal humoral response requires T-cell help; however, it has been questioned if this help comes exclusively from alphabeta-T cells or whether gammadelta-T cells also contribute. We have attempted to answer this question by studying the humoral response in T-cell receptor alpha-chain knockout (alpha-/-) mice, which lack the alphabetaT cell subset. Two model antigens were used to characterize the response: the thymus-independent (TI) antigen native dextran B512 (Dx), and the thymus-dependent (TD) antigen heat shock protein (HSP65) from Mycobacterium tuberculosis. When challenged with Dx, the alpha-/- mice elicited a strong antibody response and formed rudimentary germinal centres (GCs), a T-cell dependent reaction. In contrast, the humoral response to HSP65 was poor. However, alpha-/- mice became primed when challenged with HSP65, because when supplemented with wild-type thymocytes, the antigen-primed animals were able to mount a stronger response than the nonprimed ones when challenged with HSP65. A crucial step seems to be the collaboration between gammadeltaT cells and antigen presenting cells (APCs), as splenocytes from alpha-/- mice were able to respond to HSP65 in an environment containing primed-APCs. Based on these results, we propose a model for B-cell activation in the alpha-/- mice.

Granulysin-dependent killing of intracellular and extracellular Mycobacterium tuberculosis by Vgamma9/Vdelta2 T lymphocytes

Contribution of Vgamma9/Vdelta2 T lymphocytes to immune protection against Mycobacterium tuberculosis is still a matter of debate. It was reported earlier that Vgamma9/Vdelta2 T lymphocytes kill macrophages harboring live M. tuberculosis through a granule-dependent mechanism that results in killing of intracellular bacilli. This study found that Vgamma9/Vdelta2 T lymphocytes reduce the viability of both extracellular and intracellular M. tuberculosis. Granulysin and perforin, both detected in Vgamma9/Vdelta2 T lymphocytes, play a major role, which indicates that Vgamma9/Vdelta2 T lymphocytes directly contribute to a protective host response against M. tuberculosis infection.

Effective anti-tumor immunity induced in mice by a two-step vaccination protocol

BACKGROUND

TS/A cells (a Balb/c-derived tumor cell line), when injected into syngenic mice, give rise to rapidly growing tumors. In this study, a vaccination protocol was established which was able to elicit an immune response effective in controlling tumor growth.

MATERIALS AND METHODS

T19.2.1, a TS/A clone enginereed to stably express the mycobacterial cell wall-associated 19-kDa lipoprotein, was used as cell vaccine to immunize Mycobacterium Bovis-BCG pre-immunized Balb/c mice.

RESULTS

Mice receiving the two-step vaccination protocol were able to develop a strong anti-TS/A DTH reaction. Moreover, following a challenge with wild-type TS/A cells, some vaccinated animals rejected the tumor and the remaining animals showed a significantly increased survival in respect to controls.

CONCLUSION

The expression on TS/A cells of the mycobacterial 19-kDa antigen, recognised in the context of a pre-existing memory immune response, promotes the immunological recognition of the otherwise non-immunogenic wild-type TS/A cells.

Intranasal vaccination of mice against infection with Mycobacterium tuberculosis

The intranasal (i.n.) route of immunisation, has recently been of active interest in endeavours to improve the efficacy of vaccination against a number of respiratory infections. Here, we examined the outcome of tuberculous infection in BALB/c mice. I.n. application of the BCG-Pasteur strain was found to be highly protective against challenge infection with the pathogenic H37Rv strain given after a 4-week interval, reflected by the 100-fold reduction of CFUs in both lungs and spleens. Vaccination with the recombinant PstS-1 antigen and cholera toxin significantly protected against the challenge given 10 days later, but only marginally after 12 weeks. Histological examination showed, that i.n. vaccination abrogated the confluent infiltration of lungs with inflammatory cells, which surrounds the granulomas in H37Rv challenged control mice. In conclusion, the strong protection demonstrated by BCG suggests that the i.n. route of vaccine delivery deserves further attention toward improving vaccination against tuberculosis.

Change of Th0 to Th1 cell-cytokine profile following tuberculosis chemotherapy

T cells mediate protection against tuberculosis, but little is known about their role during chemotherapy of patients with active disease. Here we examined the cytokine profile of CD4 T cells before and after four months of chemotherapy in six initial skin test anergic cases. Purified protein derivative (PPD) and 16-kDa antigen-reactive CD4 T-cell clones prior to therapy resided mostly in disease-associated body fluids and were of the Th0 (interferon (IFN)-gamma + interleukin (IL)-4) secreting profile. In contrast, the majority of postchemotherapy CD4 T-cell clones originated from blood and were of the IFN-gamma secreting Th1 type. However, the recognition of several peptides derived from the 16-kDa antigen was not significantly different between the Th1 and Th0 clones. We conclude that chemotherapy shifts CD4 T cells from the affected body fluids to the blood circulation, accompanied by a change from Th0 to Th1 cytokine profile.

Transmission of IgA and IgG monoclonal antibodies to mucosal fluids following intranasal or parenteral delivery

BACKGROUND

The efficacy by which passive antibodies can reach the lungs could be important for the outcome of immunotherapy of respiratory pulmonary infections. We examined how transmission to a number of mucosal sites is affected by the route of inoculation.

METHODS

Transmission of newly raised IgA class Mabs against mycobacterial surface antigens to saliva, lung or vaginal lavage, bile and serum of BALB/c mice was compared with existing IgG Mabs. ELISA was used for testing body fluids obtained 1-24 h after intranasal or intravenous inoculation and 1-7 days following back-pack tumour growth of hybridomas.

RESULTS

Intranasal inoculation resulted in a rapid rise and high levels of both IgA and IgG class Mabs in lung lavage. In contrast, following intravenous Mab injection or back-pack tumour growth of hybridoma cells, effective lung transmission was observed for the IgG1 and IgG2b MAbs, but not for the IgA Mabs. The secretory component was acquired by the transmitted IgA MAbs in the mucosal fluids, but not in the serum. Nevertheless, the time course of mucosal IgA antibody levels was similar to that of the tested IgG Mabs. Furthermore, the relative proportion of transmission to saliva and bile varied between individual Mabs indicating a role of tissue-specific, immunoglobulin class-unrelated mechanisms.

CONCLUSIONS

Intranasal, rather than parenteral inoculation of mice is required for the efficient delivery of IgA antibodies against respiratory pulmonary pathogens. Interestingly, IgA-secretory component complexing of intranasally applied Mabs did not significantly influence their persistence in the lungs.

Vgamma9/Vdelta2 T lymphocytes reduce the viability of intracellular Mycobacterium tuberculosis

An effective immune response against the intracellular pathogen Mycobacterium tuberculosis is strictly dependent on T cell activation. Although this protective response mainly depends on local release of pro-inflammatory cytokines by Th1 CD4(+) T cells, contribution of Vgamma9 / Vdelta2 T lymphocytes to immune protection against this pathogen is suggested by the antimycobacterial reactivity of this subset and its ability to produce large amounts of Th1 cytokines. Here we show that Vgamma9 / Vdelta2 T lymphocytes kill macrophages harboring live M. tuberculosis. The cytotoxic activity of Vgamma9 / Vdelta2 T lymphocytes was not MHC class I or class II restricted but was blocked by anti-TCR monoclonal antibodies, thus indicating that it involved specific interaction between the TCR and the target cell. The cytotoxicity of Vgamma9 / Vdelta2 T lymphocytes was not mediated by TNF-alpha or Fas-Fas ligand, but was shown to occur through a granule-dependent mechanism that resulted in reduction of the viability of intracellular bacilli. Perforin was shown to play an important role in killing of both infected macrophages and intracellular mycobacteria. These data strongly suggest that Vgamma9 / Vdelta2 T lymphocytes contribute to the host defense against M. tuberculosis infection.

Recessive expression of the H2A-controlled immune response phenotype depends critically on antigen dose

Major histocompatibility complex (MHC) alleles acting as immune response genes are coexpressed in heterozygous individuals and therefore control of immune responses is usually codominant. As an exception to this rule, however, several examples of recessive immune responses have been ascribed to regulatory, e.g. suppressive, interactions. We report here that the recessive phenotype of both antibody and T-cell responses to the mycobacterial 16 000-MW antigen depends critically on a low antigen dose for immunization. On the basis of similar responses in hemi- and heterozygous mice, we suggest that the mechanism of recessive MHC control does not involve regulation by the low-responder allele. We also demonstrated mixed haplotype restriction of peptide recognition for a significant fraction of high-antigen-dose primed T cells. Their paucity under limiting antigen dose conditions may lead to the recessive expression of MHC control. In conclusion, our results suggest that recessive MHC control can be explained as a simple gene dosage effect under conditions where antigen is limiting, without a need for regulatory mechanisms.

Ligand-specific alphabeta and gammadelta T cell responses in childhood tuberculosis

The alphabeta and gammadelta T cell responses were analyzed in the peripheral blood of children affected by active tuberculosis (TB) and in healthy children who tested positive (PPD+) or negative (PPD-) for purified protein derivative. PPD+ healthy and diseased children responded equally well to PPD in vitro. In contrast, only 18% of PPD+ TB patients responded to peptide p38G derived from the 38-kDa protein of Mycobacterium tuberculosis. Analysis of the whole gammadelta T cell population and of its Vgamma9/Vdelta2 subset showed similar frequencies in PPD+ children with TB and in healthy PPD+ and PPD- children. Vgamma9/Vdelta2 cells from children with TB responded to 5 different phosphoantigens similarly to those from healthy PPD+ children, but healthy PPD- children responded very poorly. Chemotherapy had contrasting effects on the tested lymphocyte population, represented by increase of alphabeta and decline of Vgamma9/Vdelta2 T cell responses. T cell responses in childhood TB may be similar to those in adult TB.

Enhancement of the T cell response to a mycobacterial peptide by conjugation to synthetic branched polypeptide

A peptide-based approach towards improving the immunodiagnosis of, and vaccination against, tuberculosis faces the problems of MHC restriction of T cell recognition and the poor immunogenicity of peptides in the absence of adjuvant. We sought to compensate this by the use of synthetic branched polypeptides of the poly[Lys-(Xi-DL-Alam)] type, containing a glutamic acid residue (EAK), and further modified either by succinylation (SucEAK) or acetylation (AcEAK). These carriers were conjugated to two permissively recognized peptides of Mycobacterium tuberculosis. The 38p350 - 369-SucEAK conjugate enhanced IFN-gamma production more than 13-fold (from 22.6 to 294 pg / ml, p = 0.001) in peripheral blood mononuclear cells from healthy subjects, and 8.7-fold (p = 0. 012) in cells from tuberculosis patients. The effect was dependent on the carrier used and on covalent linkage of SucEAK to 38p350 - 369. An increased response occurred best in cells from subjects bearing at least one HLA-DR allele for which 38p350 - 369 had high binding affinity and required cellular processing of the conjugate as inhibitors (chloroquine and wortmannin) blocked the IFN-gamma response. SucEAK conjugation of peptide 16p91 - 110 did not significantly increase IFN-gamma production, indicating that the ability of conjugation to enhance the response was peptide structure dependent. These data indicate that the use of SucEAK polymer coupled with permissively recognized peptides could contribute to the development of an improved immunodiagnostic or vaccine reagent for tuberculosis.

Broad clonal heterogeneity of antigen-specific CD4+ T-cells localizing at the site of disease during tuberculosis

The repertoire of CD4+ T-lymphocytes was investigated in six patients affected by tuberculosis, who had a negative PPD skin test at diagnosis. Polyclonal CD4+ T-cell lines from the peripheral blood failed to proliferate to PPD and to the 16- or 38-kDa proteins of Mycobacterium tuberculosis, while CD4+ T-cell lines from the site of disease responded to PPD, and to the 16- and 38-kDa proteins, and derived epitopes in vitro. The repertoire of CD4+ T-cells accumulating at the site of disease was found to be widely heterogeneous as demonstrated by the finding that at least seven different peptides from the 16- and 38-kDa proteins were recognized by every patient. These results indicate that CD4+ T-cells localized at the site of disease in tuberculosis recognize a vast array of M. tuberculosis epitopes.

Sequestration of T lymphocytes to body fluids in tuberculosis: reversal of anergy following chemotherapy

The specificity of CD4 T lymphocytes was investigated in 6 patients affected by tuberculosis who had negative tuberculin purified protein derivative (PPD) skin tests at diagnosis. Polyclonal CD4 T cell lines from the peripheral blood failed to proliferate to PPD and to the 16- or 38-kDa proteins of Mycobacterium tuberculosis, while CD4 cell lines from the disease site responded to PPD and to the 16- and 38-kDa proteins and derived epitopes in vitro. Four months after chemotherapy, the patients became responsive to PPD. The proliferative response to PPD and to the 16- or 38-kDa proteins and their derived peptides decreased in CD4 T cell lines from the disease site and increased in lines from the peripheral blood. These results indicate that CD4 T cells recognizing a vast array of M. tuberculosis epitopes are compartmentalized at the site of disease in anergic patients but appear in peripheral blood after chemotherapy.

The role of B cells in the establishment of T cell response in mice infected with an intracellular bacteria, Listeria monocytogenes

To clarify the role of B cells in the establishment of T cell response against intracellular bacteria, B-cell-deficient (muMT-/-) mice were infected with an intracellular bacteria, Listeria monocytogenes, and T cell response against the bacteria was analyzed. On day 6 of primary Listeria infection, spleen T cells of the muMT-/- mice showed significantly lower levels of proliferative response and IFN-gamma production than those of normal infected mice after in vitro stimulation with listerial antigen. Even in the secondary Listeria infection after immunization with viable bacteria, spleen T cells of the muMT-/- mice proliferated and produced IFN-gamma against listerial antigen at significantly lower levels than those of normal immunized mice. These results demonstrate participation of B cells in priming of Listeria-specific T cells in vivo. However, B cells failed to present Listeria antigen to Listeria-specific T cells in vitro unless Listeria antigen was solubilized. Furthermore, transfer of immune serum from Listeria-infected normal mice failed to enhance the Listeria-specific T cell response of muMT-/- mice. The results indicate that B cells support the T cell response against intracellular bacteria through a mechanism other than their Ig production or antigen presentation function.

Selection of distinct Valpha/beta T-cell receptor families during in vivo and in vitro T-cell maturation

The experimental conditions influencing the use of Valphabeta TCR families were examined in lymph node (LN) cells from peptide-immunized C57BL/6 and Vbeta8.2 transgenic mice. Expanded proportions of Vbeta5, Vbeta8.2, Vbeta9, Vbeta12 and Vbeta14 positive cells and an association of Vbeta8.2 with Valpha11 was found in freshly harvested 8-day or 34-day immune LN cells. In contrast, peptide-specific T-cell lines generated in vitro from 8-day immune lymph node cells were found to be almost exclusively of the Valpha2/Vbeta12 family. However, T-cell lines originating from Vbeta8.2 transgenic mice did not show preferential Valpha usage. Anti-Vbeta8.2 antibody produced different effects: when added to cultures of LN cells from C57BL/6 or Vbeta8.2 transgenic strains, the peptide-induced proliferation was suppressed; however, following the injection of mice, subsequent in vitro proliferation and cytokine production induced by both peptide and Concanavalin A was suppressed in Vbeta8.2 transgenic, but much less in C57BL/6 mice. Hence, compensatory expansion of different Vbeta gene products occurred in vivo, but not under the employed in vitro conditions. In conclusion, these results suggest that the TCR family usage is influenced by the experimental conditions in which the T cells are selected and expanded and by the genetic potentials of the precursor pool.

Immune responses to recombinant proteins of Mycobacterium leprae

Identification of antigenic determinants of the polar immune response in leprosy may illuminate both protection and pathogenesis. Thirty subjects were studied (22 with polar disease and 8 healthy controls who were heavily exposed but disease-free) by assaying the proliferative, interferon (IFN)-gamma, and antibody responses to recombinant antigens of Mycobacterium leprae (10, 28, 36, and 65 kDa). The 10-kDa antigen elicited IFN-gamma production from all tuberculoid (TT) and borderline tuberculoid (BT) patients but little from controls, lepromatous (LL), or borderline lepromatous (BL) patients (P<.05). Production of 65-kDa-specific IFN-gamma was higher in TT/BT than in controls or LL/BL patients (P<.006). All subjects produced 65-kDa-specific antibody, but it was higher in LL/BL patients than in healthy controls, whose responses were higher than in TT/BT subjects (P=.035). The 36-kDa antibody responses were selectively increased in LL/BL subjects (P<.02). The intermediate phenotype of the controls suggests that M. leprae-specific production of IFN-gamma may contribute to pathology and to protection in leprosy.

Specificity and function of immunogenic peptides from the 35-kilodalton protein of Mycobacterium leprae

We identified a T-cell determinant of the 35-kDa antigen of Mycobacterium leprae which is discriminatory against cross-sensitization by its closely related homologue in Mycobacterium avium. From synthetic peptides covering the entire sequence, those with the highest affinity and permissive binding to purified HLA-DR molecules were evaluated for the stimulation of proliferation of peripheral blood mononuclear cells (PBMCs) from leprosy patients and healthy sensitized controls. Responses to the peptide pair 206-224, differing by four residues between M. leprae and M. avium, involved both species-specific and cross-reactive T cells. Lymph node cell proliferation in HLA-DRB1*01 transgenic mice was reciprocally species specific, but only the response to the M. leprae peptide in the context of DR1 was immunodominant. Of the cytokines in human PBMC cultures, gamma interferon production was negligible, while interleukin 10 (IL-10) responses in both patients and controls were more pronounced. IL-10 was most frequently induced by the shared 241-255 peptide, indicating that environmental cross-sensitization may skew the response toward a potentially pathogenic cytokine phenotype.

38 000 MW antigen-specific major histocompatibility complex class I restricted interferon-gamma-secreting CD8+ T cells in healthy contacts of tuberculosis

CD8+ T lymphocytes are required to protect mice against Mycobacterium tuberculosis, although in early infection the mechanism appears not to be via perforin or granzyme-mediated lysis of the infected target, and may be via interferon-gamma (IFN-gamma) production. We therefore investigated whether CD8+ T cells specific for the immunoprotective 38 000 MW antigen of M. tuberculosis could be detected in infected humans. Using a recombinant vaccinia virus expressing the 38 000 MW antigen of M. tuberculosis (rV38) and a control vaccinia virus (rVras) we demonstrated that both viruses stimulated IFN-gamma production from freshly isolated peripheral blood mononuclear cells (PBMC) in a 36-hr enzyme-linked immunospot assay. Cell depletion and antibody blockade established that the bulk of the 38 000 MW antigen-specific IFN-gamma response was mediated by CD8+, major histocompatibility complex class I-restricted T cells, whereas the anti-vaccinia virus response was predominantly mediated by CD4+ T cells. In further evaluations PBMC from all seven healthy tuberculosis-exposed contacts had a 38 000 MW antigen-specific IFN-gamma response, whereas seven patients with untreated sputum-positive pulmonary tuberculosis had very low levels of 38 000 antigen-specific IFN-gamma-producing cells. These preliminary observations demonstrate the utility of recombinant vaccinia viruses in restimulating freshly isolated CD4+ and CD8+ T cells. The bias towards a higher frequency of IFN-gamma-producing CD8+ T cells in contacts rather than patients may indicate a protective role for CD8+ cells in human tuberculosis.

T-cell recognition of mycobacterial GroES peptides in Thai leprosy patients and contacts

We report here the mapping of T-cell-stimulatory determinants of the GroES 10-kDa heat shock protein homologues from Mycobacterium leprae and Mycobacterium tuberculosis, which are known as major immunogens in mycobacterial infections. Peripheral blood mononuclear cells (PBMC) from treated tuberculoid leprosy or lepromatous leprosy patients and from healthy household or hospital staff contacts of the patients were cultured with 20 16-mer peptides covering the entire sequences of both M. leprae and M. tuberculosis GroES. The total number of recognized peptides was found to be the largest in family contacts, while responder frequencies to the individual tested peptides varied (5 to 80%) with specificity between the patient and contact groups. Proliferative responses to some peptides showed positive or negative associations of low statistical significance with DR and DQ alleles, though responses to most GroES peptides were genetically permissive. Notably, the sequence of the 25-40 peptide of M. leprae, but not that of M. tuberculosis, was more frequently stimulatory in tuberculoid leprosy patients than in either group of sensitized healthy contacts. This peptide bound to a number of HLA-DR molecules, of which HLA-DRB5*0101 had the strongest affinity. The epitope core binding to this allele was localized to the 29-to-37 sequence, and its key residue was localized to the M. leprae-specific glutamic acid at position 32. This epitope may be of interest for the development of a blood test- or skin test-based diagnostic reagent for tuberculoid leprosy, subject to further clinical evaluation in untreated patients.

Human T- and B-cell reactivity to the 16kDa alpha-crystallin protein of Mycobacterium tuberculosis

The attributes of immunodominance, predominant expression during mycobacterial dormancy and restriction to the Mycobacterium tuberculosis complex make the 16 kDa protein an important candidate for the study of the immune response in humans. We therefore investigated the relationship between T- and B-cell reactivity to the recombinant antigen and disease in a total of 127 subjects. The percentage of T-cell responders towards both the intact antigen and its permissively recognised peptide 16p91-110 was highest in healthy bacillus Calmette-Guérin (BCG)-sensitized controls (96% and 68%, respectively) and lowest in those with extensive untreated tuberculosis (26% and 18%) (P < 0.001). By contrast, antibody levels (ABT50 > 100) were highest in patients with extensive disease (46-50%) (P < 0.005). There was significantly higher production of IFN-gamma in the BCG-sensitized controls by comparison with untreated patients (P < 0.05), but complete antituberculous chemotherapy abolished this deficit in patients. The significance of these findings to immunodiagnosis and protective immunity is discussed.

Synthesis and in vitro T-cell immunogenicity of conjugates with dual specificity: attachment of epitope peptides of 16 and 38 kDa proteins from Mycobacterium tuberculosis to branched polypeptide

T-cell epitope containing peptides covalently attached to macromolecular carriers can be considered as synthetic immunogens for the development of skin-test diagnostics and of vaccines. As a carrier, an amphoteric branched chain polypeptide, poly[Lys-(Glui-DL-Alam)] (EAK) with poly(L-lysine) backbone has been used. This polypeptide with free alpha-amino and gamma-carboxyl groups at the end of the side chains was conjugated with peptides representing two immunodominant regions of the 16 and 38 kDa proteins of Mycobacterium tuberculosis, respectively. Peptide C91SEFAYGSFVRTVSLPVGADE110 was elongated by Cys at the N-terminal and attached to the carrier containing protected SH groups to form disulfide bridges. Peptide 65FNLWGPAFHERYPNVTITA83 was conjugated to the 3-(2-pyridyldithio)propionic acid N-hydroxysuccinimide ester (SPDP) modified and acetylated EAK by introducing amide bond between the free alpha-amino group of peptide and the free gamma-COOH group of Glu at the terminal position of the branches. This strategy lead to chemically well-defined synthetic immunogens that contain two different epitopes in multiple copies covalently linked to a synthetic branched polypeptide carrier. In vitro T-cell immunogenicity of a prototype conjugate was studied using T-cell hybridomas, lymph node cells from 38 kDa protein immunized mice, and human peripheral blood mononuclear cell (PBMC) cultures from sensitized individuals. These data document that the specific T-cell stimulatory effect of each mycobacterial epitope was maintained in this conjugate. Taken together, these findings suggest that it is feasible to use a biodegradable polymeric polypeptide for producing macromolecular bioconjugates for the stimulation of T-cell responses.

Peptide-specific T cell response to Mycobacterium tuberculosis: clinical spectrum, compartmentalization, and effect of chemotherapy

The T cell repertoire of 59 patients with untreated tuberculosis was compared with that of 46 bacille Calmette-Guérin-vaccinated controls by assaying the proliferative responses to six permissively recognized peptides from the 16-, 19-, and 38-kDa molecules of Mycobacterium tuberculosis. A trend from higher to lower reactivity following this order: vaccinated controls > lymph node disease > localized extrapulmonary > pulmonary > pleural was seen for 4 of the peptides (P < .03). The decreased response of blood lymphocytes from patients with pleural tuberculosis was partially accounted for by sequestration of peptide-responsive cells within the pleural fluid. Chemotherapy "reversed" the depressed proliferative responses of patients with pulmonary and pleural tuberculosis depending on the peptide origin, being greatest for peptides of 16 kDa, transient for those of 19 kDa, and least for those of 38 kDa. These data demonstrate antigen specificity in the decreased responsiveness of patients with tuberculosis.

Predominant recognition of species-specific determinants of the GroES homologues from Mycobacterium leprae and M. tuberculosis

The Mycobacterium leprae and M. tuberculosis 10,000 MW heat-shock protein homologues of GroES have previously been identified as major immunogens for human T cells. We used synthetic peptides to characterize the determinants recognized by murine T cells. The findings suggest that, despite 90% sequence identity between these two proteins, T cells recognize prominently the species-specific determinants localized within amino acid residues 21-40 and 49-72. Analysis of the molecular determinants of species-specificity for the M. leprae GroES sequence 25-40, using T-cell hybridomas and major histocompatibility complex (MHC)-binding assays, led to the identification of epitope cores and critical residues. Interestingly, closely overlapping epitope cores were found to be restricted by either H-2Ad (24-34) or H-2Ed (28-34). Furthermore, the site recognized by the M. leprae-specific monoclonal antibodies ML06 and ML10 was also localized in the overlapping sequences 25-31 and 25-29. In conclusion, we demonstrated that immunodominant species-specific T- and B-cell epitopes can be found in a mycobacterial heat-shock protein despite its highly conserved amino acid sequence. This finding suggests the feasibility of identifying a sufficient number of M. leprae-specific determinants for a composite T-cell immunodiagnostic reagent for tuberculoid leprosy.

Modulation of peptide specific T cell responses by non-native flanking regions

The deduced core (75RYPNVTI81) from a T-cell stimulatory epitope of the 38 kDa protein of M. tuberculosis was studied to identify the structural elements required for the creation of a synthetic peptide antigen from an epitope core, which alone was not capable of inducing CD4+ T-cell responses. Peptides were prepared with extensions composed of native and/or non-native sequences to clarify the role of the flanking regions adjacent to the epitope core. Their binding to isolated H-2-Ab MHC glycoprotein as well as T-cell stimulatory capacity were assayed using a specific murine hybridoma T-cell line [38.H6], lymph node cells from the native 20-mer peptide primed C57BL/10 mice and human PBMCs from sensitised individuals. Elongation of the epitope core by four alanines at both N- and C-terminals resulted in a 15-mer peptide A4-75-81-A4 which was stimulatory for hybridoma T-cells and showed a small decrease in H-2-Ab binding. Substitution of one Ala by Ser in the N-terminal flank had pronounced effect and peptide A2SA-75-81-A4 proved to be more effective than the native 20-mer sequence in the hybridoma as well as in the LN cell proliferation assays. The binding of this peptide and that of the native one were similar. Testing in human PBMC cultures from eight PPD positive individuals showed that in 50% of the donors' cells responded to the 'artificial' A2SA-75-81-A4 peptide. These results suggest that it is possible to construct simple, synthetic CD4+ T-cell stimulatory peptides of high potency from a non-stimulatory, 'silent' epitope core by addition of flanking residues not part of the native sequence.

Specificity of CD8+ T cells from subunit-vaccinated and infected H-2b mice recognizing the 38 kDa antigen of Mycobacterium tuberculosis

CD8+ T cells have been implicated in protective anti-tuberculous immune responses, but little is known about the identity of mycobacterial antigens recognized by CD8+ T cells. In this study we identified the Mycobacterium tuberculosis 38 kDa protein as a target for murine CD8+ cytotoxic T lymphocytes (CTL) which were induced by vaccination of C57BL/6 mice with DNA delivered with a plasmid, with transfected tumour cells or by infection with tubercle bacilli. Using overlapping synthetic peptides covering the whole protein sequence, peptides predicted to contain H-2Kb or H-2Db motifs, as well as naturally processed peptides, we were able to identify CTL epitopes. Differences were demonstrated in peptide specificity between CTL from immunized or M. tuberculosis-infected mice. The identified CTL epitopes could be important for future analysis of the involvement of CD8+ T cells in M. tuberculosis infections and for vaccine development.

Vaccination with recombinant vaccinia viruses protects mice against Mycobacterium tuberculosis infection

A number of subunit-based vaccine candidates have recently begun to erode the exclusive position of Mycobacterium bovis bacillus Calmette-Guérin (BCG), which gives unpredictable and highly variable protection against tuberculosis. In this paper we investigated the protective capacity of the 19,000 MW and 38,000 MW glyco-lipoproteins of M. tuberculosis expressed by recombinant vaccinia viruses in a mouse Mycobacterium tuberculosis infection model. Both proteins were expressed at high levels by recombinant vaccinia-infected cells. In addition, two inoculations of C57B1/6 mice with either recombinant vaccinia virus significantly reduced the bacterial counts in the lungs of M. tuberculosis H37Rv-infected mice, when compared with the group infected with control virus. This is the first report of protection against tuberculous infection using recombinant vaccinia viruses with results that suggest that secreted glyco-lipoproteins in conjunction with the vaccinia vector represent suitable candidates for further vaccine-related studies.

The effect of glucosaminylmuramyl dipeptide injection to mice on the course of tuberculous infection and in vitro superoxide anion production

Immunotherapy as an adjunct to chemotherapy is of interest for optimizing therapeutic regimens for tuberculosis. In this context, we investigated the influence and mode of action ofglucosaminylmuramyl dipeptide (GMDP) in mouse experimental models. Intermittent injections of GMDP to Mycobacterium tuberculosis-infected mice reduced the viable bacilli in the lungs, but increased the counts in the spleens at 16 weeks, but not at earlier harvests after infection. Injections of GMDP selectively ameliorated also in the lungs the spontaneous relapse of infection following chemotherapy. The mode of GMDP action was examined in respect of superoxide anion production. The O2 production by phorbol myristate-induced peritoneal macrophages in vitro was reduced by preinjection of mice with 100 microg of GMDP. Notably, this outcome contrasts and can also override the previously known enhancing effect of MDP on O2- production. The inhibitory activity of GMDP became even more pronounced when testing macrophages from Mycobacterium bovis BCG-infected mice. However, these results do not explain readily the grounds for the contrasting effects of GMDP on the growth patterns of tubercle bacilli in the lungs and spleens. Although the observed effects on bacillary counts have been modest, such action of GMDP could represent a beneficial adjunct to suitably formulated chemotherapeutic regimens.

Functions and specificity of T cells following nucleic acid vaccination of mice against Mycobacterium tuberculosis infection

The 38-kDa glycolipoprotein of Mycobacterium tuberculosis has been known to evoke prominent T cell and Ab responses in patients with active tuberculosis. In this study, we investigated its protective capacity using plasmid DNA immunization in a mouse experimental model. Prior knowledge of several antigenic determinants has been beneficial for analyzing the phenotype and specificity of T cells, which determine the efficacy of this vaccination procedure. C57BL/6 mice responded to the 38-kDa gene-pcDNA3 plasmid with strong CD4+ Th1 and CD8+ cytotoxic T cell responses of the IFN-gamma-producing Tc1 phenotype. After challenge with virulent tubercle bacilli, the bacterial load in the spleens and lungs of vaccinated mice was reduced to a level similar to that imparted by Mycobacterium bovis Bacille Calmette-Guérin vaccination. Notably, the specificity of CD4+ and CD8+ T cells from DNA-vaccinated and tubercle-infected mice was found to be strikingly different in respect of several peptide epitopes. The identified peptides recognized by T cells from protected mice are of further interest for the development of subunit-based vaccines against tuberculosis.

Functions and specificity of T cells following nucleic acid vaccination of mice against Mycobacterium tuberculosis infection

The 38-kDa glycolipoprotein of Mycobacterium tuberculosis has been known to evoke prominent T cell and Ab responses in patients with active tuberculosis. In this study, we investigated its protective capacity using plasmid DNA immunization in a mouse experimental model. Prior knowledge of several antigenic determinants has been beneficial for analyzing the phenotype and specificity of T cells, which determine the efficacy of this vaccination procedure. C57BL/6 mice responded to the 38-kDa gene-pcDNA3 plasmid with strong CD4+ Th1 and CD8+ cytotoxic T cell responses of the IFN-gamma-producing Tc1 phenotype. After challenge with virulent tubercle bacilli, the bacterial load in the spleens and lungs of vaccinated mice was reduced to a level similar to that imparted by Mycobacterium bovis Bacille Calmette-Guérin vaccination. Notably, the specificity of CD4+ and CD8+ T cells from DNA-vaccinated and tubercle-infected mice was found to be strikingly different in respect of several peptide epitopes. The identified peptides recognized by T cells from protected mice are of further interest for the development of subunit-based vaccines against tuberculosis.

Mutagenesis of an immunodominant T cell epitope can affect recognition of different T and B determinants within the same antigen

The effects of mutagenesis of residues of a major T cell epitope were investigated in order to expand knowledge from synthetic peptides to the naturally processed antigen. The impact of substitutions within the core of the immunodominant p61-80/PT19 mycobacterial epitope was ascertained in respect of this epitope per se, or of a C-terminal (140-159) overlapping T/B epitope and of a conformational B epitope. The core substitution A71L impaired T immunogenicity of the target epitope within the protein, but not in the peptide, whereas the N73A substitution impaired the responses in both instances. Notably, each of these single amino acid mutations abrogated the T but not the B immunogenicity of the C-terminal epitope. Furthermore, mutation of five core residues (71-76) also ablated expression of a monoclonal antibody defined conformational B epitope. In conclusion, immunological analysis of mutated proteins revealed functional associations between topographically distinct antigenic determinants which may account for the previously observed differences in the specificity of immune responses between immunised and infected hosts.

Evaluation of the recombinant 38-kilodalton antigen of Mycobacterium tuberculosis as a potential immunodiagnostic reagent

The diagnosis of infection caused by Mycobacterium tuberculosis is of increased public health concern following increases in the number of cases in developed countries and major increases in developing countries associated with the spread of human immunodeficiency virus (HIV) infection. The specificity of purified protein derivative skin testing for the detection of infection is compromised by exposure to environmental mycobacteria. Examination of sputum detects the most infectious patients, but not those with extrapulmonary disease. The 38-kDa antigen of M. tuberculosis contains two M. tuberculosis-specific B-cell epitopes. We overexpressed the gene for this antigen in Escherichia coli and evaluated the recombinant product in in vitro assays of T-cell function and as a target for the antibody response in humans. The sensitivity and specificity of the antigen as a skin test reagent were also assessed in outbred guinea pigs. We found that 69% of healthy sensitized humans recognize the antigen in vitro, as manifested by both cell proliferation and the production of gamma interferon. Untreated patients initially have a lower frequency of response (38%); this recovers to 72% during therapy. A total of 292 patients (20 with HIV coinfection) and 58 controls were examined for production of antibody to the 38-kDa antigen by using a commercially available kit. The sensitivity of the test in comparison with that of culture was 72.6%, and the specificity was 94.9%. The antigen was also tested for its ability to induce skin reactions in outbred guinea pigs sensitized by various mycobacterial species. The antigen provoked significant skin reactions in M. tuberculosis-, M. bovis BCG-, and M. intracellulare-sensitized animals. The significance of these findings and the usefulness of this antigen in immunodiagnosis are discussed.

Distinct conformations of a peptide bound to HLA-DR1 or DRB5*0101 suggested by molecular modelling

The conformation of peptides when bound to different HLA class II molecules is of interest in the study of specificity and function of responding T cells. Here, we report the investigation of the HLA-DR binding profiles of an immunodominant and HLA-promiscuous mycobacterial peptide, p38G. Its binding affinities were found to be high for DR1, moderate for DR2, DR7 and DR8, low for DR4, DR5, DR6 and DR9, and below detection for DR3. The minimum peptide length required for binding was, in the majority of cases, nine residues and 11 in two instances (DR2 and DR4). Peptide binding to DR2 was attributed to the DRB5*0101 and not to the DRB1*1501 gene product. Substitution analysis of the amino acid residues involved in binding to DR1 and DRB5*0101 identified F-354 as the common primary contact residue (P1), while allele-specific differences were found in positions P4, P6 and in the C-terminal anchor residue (valine at P9 for DR1 or lysine at P10 for DRB5*0101). Computer-assisted evaluation of these empirical data produced a molecular model, suggesting that the peptide binds to DR1 in an elongated conformation, similar to that of other peptide MHC class II complexes. In contrast, the DRB5*0101 bound peptide is likely to be kinked, which so far was considered characteristic only for peptides within MHC class I complexes. The different conformations imposed on the same peptide by distinct HLA alleles may represent an important mechanism for the control of T cell responses.

Increase of tuberculous infection in the organs of B cell-deficient mice

Protective immunity against infection with Mycobacterium tuberculosis is imparted by T cells rather than antibodies, but B cells can play a role as antigen-presenting cells and in granuloma formation. We re-evaluated the role of B cells in the course of tuberculous infection in mu-chain knock-out (Ig-) mice. Surprisingly, the organs of M. tuberculosis-infected Ig- mice were found to have three- to eight-fold elevated counts of viable bacilli compared with normal littermates at 3-6 weeks post-infection. Splenic interferon-gamma responses to whole antigen were unimpaired, whilst proliferation to certain mycobacterial peptides was found to be diminished. However, bacille Calmette-Guérin (BCG) vaccination significantly reduced the infection in Ig- mice. The mechanisms by which B cells can influence primary tuberculous infection need further study.

Duplication of genes encoding the immunodominant 38 kDa antigen in Mycobacterium intracellulare

Mycobacterium avium is a causative agent of mycobacterioses in systemically immunocompromised individuals, whereas Mycobacterium intracellulare is responsible for causing infections in relatively immunocompetent hosts. In an attempt to identify components that could be involved in virulence, we characterised the 38 kDa-encoding gene of M intracellulare that is absent in M. avium. This antigen cross reacts immunologically with a major 38 kDa antigen of M. tuberculosis, and both antigens are homologues of the phosphate transport subunit S (PstS) of the pst complex of Escherichia coli. Unlike the M. tuberculosis complex the M. intracellulare coding gene was found to be duplicated. We also identified and characterised other pst genes that may constitute an operon. Considering that multiple isoforms of PstS are present in mycobacteria the possible role of pstS1 genes for pathogenesis is discussed.

T cell responses to a mixture of Mycobacterium tuberculosis peptides with complementary HLA-DR binding profiles

The T cell response to a mixture of eight peptides derived from sequences of the Mycobacterium tuberculosis 16-, 19- and 38-kD antigens (MTBmix-8) has been studied. The peptides were selected on the basis of complementary binding to nine HLA-DR molecules (HLA-DR1 to DR9). MTBmix-8 at 6.25 and 50 micrograms/ml gave rise to significant stimulation (P < 0.05) of peripheral blood mononuclear cells (PBMC) from healthy tuberculin-positive and both untreated and treated diseased subjects, but not in any of a control group of healthy tuberculin-negative subjects. MTB-mix-8 stimulated proliferation of PBMC from healthy tuberculin-positive individuals at lower concentrations than the individual component peptides. However, the maximal stimulation achieved was only slightly higher than that achieved with individual peptides. MTBmix-8 also stimulated the production of interferon-gamma (IFN-gamma) in vitro. Using the mean +/- 2 s.d. of the values for IFN-gamma production in the tuberculin-negative population as a cut-off, MTBmix-8 at 6.25 micrograms/ml was able to detect infection with a sensitivity of 100% in untreated patients, 87% in treated patients, and 82% in tuberculin-positive controls. The corresponding figures for the most potent single peptide (16p91-110) were: 66% in untreated patients, 71% in treated patients and only 42% in controls. Thus, using the IFN-gamma-based assay, which has the additional advantages of speed and does not require radioactivity, the mixture of peptides is more sensitive than single peptides in diagnosing infection.

Immunogenicity of peptides for B cells is not impaired by overlapping T-cell epitope topology

The epitope specificity of T-cell help to B cells and of surface immunoglobulin-mediated B-cell-binding of antigens usually involves topographically distinct antigenic determinants. The possibility of cross-recognition of the same peptide sequence by both T cells and antibodies has been a matter of conflicting opinions. We investigated this subject by detailed mapping of T- and B-cell epitopes within four immunogenic mycobacterial peptides. The identified core sequences of T- and B-cell epitopes showed different topology within each peptide: they were partially overlapping or adjacent in two P38-derived peptides, but entirely overlapping in two P19-derived peptides. The critically important result using the two truncated peptides (P19/67-78 and P19/146-155) containing only the fully overlapping epitope cores was, that they retained full potency for inducing antibody responses. However, despite this desirable overlap of determinants, antipeptide sera failed to block the proliferation of corresponding T-cell hybridomas. We conclude, that our study, in contrast to previous findings, suggests that overlapping topology of T- and B-cell epitopes within synthetic peptides does not necessarily impair B-cell immunogenicity.

Multiple sclerosis: a protective or a pathogenic role for heat shock protein 60 in the central nervous system?

The stress proteins belonging to the heat shock protein 60 (hsp6O) family of molecular chaperones with known immunogenic properties are expressed at increased levels in a number of autoimmune conditions. Because previous studies from this laboratory suggested that hsp6O may be involved in the pathogenesis of the chronic multiple sclerosis (MS) plaque, we have examined autopsied central nervous system tissue from 10 cases of MS, ranging in clinical history from acute to chronic inactive. MS lesions ranged from acute, actively demyelinating and edematous, to fibrous astrogliotic and chronically demyelinated. As controls, central nervous system tissue from other neurologic diseases and nonneurologic conditions was used. Frozen, paraffin, and epoxy-embedded sections were studied immunocytochemically with the ML30 mAb to hsp6O. Acute MS lesions displayed the greatest reactivity, with particularly prominent staining of hypertrophic astrocytes, reactive macrophages, and hyperplastic oligodendrocytes. In all these cells, elevated expression occurred in the constitutive site for hsp6O (mitochondria) and within the cytosol, which is suggestive of a shift in expression. The hsp6O-reactive oligodendrocytes were structurally intact. Chronic active MS lesions also revealed the highest levels of hsp6O in hypertrophic astrocytes and oligodendrocytes. Chronic silent MS lesions displayed elevated hsp6O in hypertrophic astrocytes only while constitutive expression occurred elsewhere in the central nervous system at levels slightly higher than normal. Other neurologic disease tissue displayed expression elevated above that found in nonneurologic cases, but this was considerably less than that seen in acute MS. Of the other neurologic diseases, AIDS encephalitis revealed the greatest activity for hsp6O, with both mitochondrial and cytosolic staining of astrocytes. It is proposed that the high levels of hsp6O in hyperplastic, structurally intact oligodendrocytes in acute MS lesions may bespeak a protective mechanism, whereas hsp6O in chronic active lesions may serve a pathogenic role in the later depletion of these cells.

Lack of production of the 19-kDa glycolipoprotein in certain strains of Mycobacterium tuberculosis

The 19-kDa glycolipoprotein of Mycobacterium tuberculosis (PT19) is a prominent antigen recognized by both T cells and antibodies from tuberculosis patients. We report here that two strains, I2646 and S1, when grown either in bacteriological culture or during infection of mice, do not produce this constituent, as judged by ELISA and Western blot assays. Southern blot analysis of the chromosomal DNA showed that both strains displayed the restriction fragment as in H37Rv DNA, suggesting the lack of gross gene alterations. Sequence analysis revealed multiple microlesions including small deletions, point mutations and nucleotide insertions, leading to either premature termination or alteration of open reading frame in both strains. Transformation of both mutant strains with the wild-type gene on a multicopy plasmid resulted in overproduction of native PT19. Infection of mice suggested that the I2646 is of low virulence and that the transformant-producing native PT19 exhibited higher virulence, as assessed by viable counts and gross lesions in the infected organs. The mechanisms and significance of the lack of PT19 production in certain M. tuberculosis strains is discussed.

Genetic and serovar typing of clinical isolates of the Mycobacterium avium-intracellulare complex

SETTING

One hundred and thirty-four Mycobacterium avium-intracellulare complex (MAC) isolates were obtained from 121 patients in the UK.

OBJECTIVE

To compare serotyping and genetic analysis for species identification of MAC isolates from patients with and without the acquired immunodeficiency syndrome (AIDS).

DESIGN

Clinical MAC isolates were cultured and analyzed by serotyping, the commercially available Accuprobe kit, hybridization with genes coding for the 19 kDa and 38 kDa antigens of M. tuberculosis and fingerprinting with the pMB22 probe derived from M. paratuberculosis.

RESULTS

Species classification on the basis of genetic analysis was similar to serovar typing, with only exceptional discrepancies. Serovar prevalence was different in the two groups of patients, and different from those reported in other countries. MAC isolates from AIDS patients were exclusively M. avium, whereas patients without AIDS had MAC infections with M. avium and M. intracellulare in about equal proportion. M. intracellulare clinical isolates were genetically more heterogeneous than M. avium. Only M. intracellulare hybridized with the 38 kDa gene probe.

CONCLUSIONS

Serovars are strongly linked with species in clinical MAC isolates, confirming results previously obtained with reference strains. M. intracellulare can be easily identified by the presence of a 38 kDa gene.

Cross-recognition by T cells of an epitope shared by two unrelated mycobacterial antigens

The molecular mimicry represented by cross-recognition of determinants shared by unrelated antigens by antibodies or T cells is of broad immunological interest. In this study, we analyzed the cross-recognition by CD4+ T cells of a peptide epitope shared by two mycobacterial proteins of diverse sequence, represented by the 19-kDa antigen of Mycobacterium tuberculosis and the 28-kDa antigen of Mycobacterium leprae. This epitope was immunodominant with respect to the 19-kDa antigen, but cryptic in relation to the 28-kDa antigen. The cross-reactive epitope cores were identified by Pepscan window analysis and found to be eight residues long in both antigens (residues 69-76 and 127-134). Alignment of these octameric sequences revealed two identical and five conservatively related amino acids. Within the epitope core, two residues (73Asn and 76Ile) were identified as critical for recognition on the basis of inhibition of the cross-reactive T cell proliferative response using singly substituted analog peptides. These results suggest that T cell cross-reactive epitopes can exist in proteins with apparently not more than random levels of sequence homology. Their potential for unsuspected cross-sensitization may play a role in the maintenance of T cell memory, in the pathogenesis of autoimmune diseases and possibly in a wide range of host immune responses to infectious pathogens.

H-2-associated effects of flanking residues on the recognition of a permissive mycobacterial T-cell epitope

Previously we have identified an immunodominant, eight-residue, epitope core sequence (TAAGNVNI) from the 19,000 MW protein of Mycobacterium tuberculosis, which is recognized in the context of multiple H-2 I-A molecules. In this study, the role of residues flanking this T-cell epitope core was examined, using a series of 20 mer analogue peptides in which the native flanking residues were progressively replaced with L-alanine. Analogue peptides were tested for their capacity to stimulate a CD4+ 19,000 MW protein-specific T-cell line, revealing that all but one N-terminal flanking residue could be replaced collectively by alanine without significant loss of stimulatory activity. However, clear H-2-associated differences in the requirement for flanking residues were demonstrated with peptide-specific T-cell hybridomas. In particular, H-2d-derived hybridomas were much more stringent in their requirement for flanking residues than were H-2b hybridomas. All polyalanine-substituted peptides bound I-Ab molecules, with affinities similar to the native unsubstituted peptide. In contrast, significantly reduced binding to I-Ad was observed with several analogue peptides, although without a clear relationship to the degree of substitution. Furthermore, in H-2b mice, neither immunogenicity nor cross-reactivity with the native peptide showed a clear inverse relationship with respect to the degree of alanine substitution. The results presented in this paper indicate that flanking residues can influence T-cell specificity and that these effects may be controlled by major histocompatibility complex (MHC) haplotype.

Ribosomal internal transcribed spacer sequences are identical among Mycobacterium avium-intracellulare complex isolates from AIDS patients, but vary among isolates from elderly pulmonary disease patients

Sequencing 280 bp of the internal transcribed spacer (ITS) between the 16S and 23S rRNA genes in a collection of 46 clinical isolates of the Mycobacterium avium-intracellulare complex (MAI complex) identified nine different sequences, grouping these isolates in nine 'ITS sequevars'. This analysis extends the subdivision within the MAI complex to 18 ITS sequevars and also improves discrimination from other mycobacterial species. Evaluation of the sequevar grouping among different clinical sources revealed strong association of the M. avium sequevar Mav-B with AIDS and with lymphadenitis in children (18 out of 20 and 3 out of 3 respectively). Isolates from elderly patients with pulmonary disease and not suspected of being HIV infected belonged predominantly to M. intracellulare ITS sequevars and sequevars not assigned to either M. avium or M. intracellulare. On the other hand, animal isolates were of both the Mav-A and Mav-B sequevars. We conclude that ITS sequevar typing is an accurate way of identifying distinct MAI complex strains. The observed differences between clinical sources suggest that ITS sequevars reflect possibly important, biologically and clinically relevant polymorphisms between MAI complex organisms.