In vivo and in vitro characterization of murine T-cell clones reactive to Mycobacterium tuberculosis

Scrutiny of Mycobacterium tuberculosis 19 kDa antigen proteoforms provides new insights in the lipoglycoprotein biogenesis paradigm

Post-translational modifications (PTMs) are essential processes conditioning the biophysical properties and biological activities of the vast majority of mature proteins. However, occurrence of several distinct PTMs on a same protein dramatically increases its molecular diversity. The comprehensive understanding of the functionalities resulting from any particular PTM association requires a highly challenging full structural description of the PTM combinations. Here, we report the in-depth exploration of the natural structural diversity of the M. tuberculosis (Mtb) virulence associated 19 kDa lipoglycoprotein antigen (LpqH) using intact protein high-resolution mass spectrometry (HR-MS) coupled to liquid chromatography. Combined top-down and bottom-up HR-MS analyses of the purified Mtb LpqH protein allow, for the first time, to uncover a complex repertoire of about 130 molecular species resulting from the intrinsically heterogeneous combination of lipidation and glycosylation together with some truncations. Direct view on the co-occurring PTMs stoichiometry reveals the presence of functionally distinct LpqH lipidation states and indicates that glycosylation is independent from lipidation. This work allowed the identification of a novel unsuspected phosphorylated form of the unprocessed preprolipoglycoprotein totally absent from the current lipoglycoprotein biogenesis pathway and providing new insights into the biogenesis and functional determinants of the mycobacterial lipoglycoprotein interacting with the host immune PRRs.

Immunoreactivity of the Mycobacterium avium subsp. paratuberculosis 19-kDa lipoprotein

BACKGROUND

The Mycobacterium tuberculosis 19-kDa lipoprotein has been reported to stimulate both T and B cell responses as well as induce a number of Th1 cytokines. In order to evaluate the Mycobacterium avium subsp. paratuberculosis (M. avium subsp. paratuberculosis) 19-kDa lipoprotein as an immunomodulator in cattle with Johne's disease, the gene encoding the 19-kDa protein (MAP0261c) was analyzed.

RESULTS

MAP0261c is conserved in mycobacteria, showing a 95% amino acid identity in M. avium subspecies avium, 84% in M. intracellulare and 76% in M. bovis and M. tuberculosis. MAP0261c was cloned, expressed, and purified as a fusion protein with the maltose-binding protein (MBP-19 kDa) in Escherichia coli. IFN-gamma production was measured from 21 naturally infected and 9 control cattle after peripheral blood mononuclear cells (PBMCs) were stimulated with a whole cell lysate (WCL) of M. avium subsp. paratuberculosis or the recombinant MBP-19 kDa. Overall, the mean response to MBP-19 kDa was not as strong as the mean response to the WCL. By comparison, cells from control, non-infected cattle did not produce IFN-gamma after stimulation with either WCL or MBP-19 kDa. To assess the humoral immune response to the 19-kDa protein, sera from cattle with clinical Johne's disease were used in immunoblot analysis. Reactivity to MBP-19 kDa protein, but not MBP alone, was observed in 9 of 14 infected cattle. Antibodies to the 19-kDa protein were not observed in 8 of 9 control cows.

CONCLUSIONS

Collectively, these results demonstrate that while the 19-kDa protein from M. avium subsp. paratuberculosis stimulates a humoral immune response and weak IFN-gamma production in infected cattle, the elicited responses are not strong enough to be used in a sensitive diagnostic assay.

Down-modulation of lung immune responses by interleukin-10 and transforming growth factor beta (TGF-beta) and analysis of TGF-beta receptors I and II in active tuberculosis

Immune factors influencing progression to active tuberculosis (TB) remain poorly defined. In this study, we investigated the expression of immunoregulatory cytokines and receptors by using lung bronchoalveolar lavage cells obtained from patients with pulmonary TB, patients with other lung diseases (OLD patients), and healthy volunteers (VOL) by using reverse transcriptase PCR, a transforming growth factor beta (TGF-beta) bioactivity assay, and an enzyme immunoassay. TB patients were significantly more likely than OLD patients to coexpress TGF-beta receptor I (RI) and RII mRNA, as well as interleukin-10 (IL-10) mRNA (thereby indicating the state of active gene transcription in the alveolar cells at harvest). In contrast, gamma interferon (IFN-gamma) and IL-2 mRNA was seen in both TB and OLD patients. Likewise, significantly elevated pulmonary steady-state protein levels of IL-10, IFN-gamma, and bioactive TGF-beta were found in TB patients versus those in OLD patients and VOL. These data suggest that the combined production of the immunosuppressants IL-10 and TGF-beta, as well as coexpression of TGF-beta RI and RII (required for cellular response to TGF-beta), may act to down-modulate host anti-Mycobacterium tuberculosis immunity and thereby allow uncontrolled bacterial replication and overt disease. Delineating the underlying mechanisms of M. tuberculosis-triggered expression of these immune elements may provide a molecular-level understanding of TB immunopathogenesis.

The alternative sigma factor SigH regulates major components of oxidative and heat stress responses in Mycobacterium tuberculosis

Mycobacterium tuberculosis is a specialized intracellular pathogen that must regulate gene expression to overcome stresses produced by host defenses during infection. SigH is an alternative sigma factor that we have previously shown plays a role in the response to stress of the saprophyte Mycobacterium smegmatis. In this work we investigated the role of sigH in the M. tuberculosis response to heat and oxidative stress. We determined that a M. tuberculosis sigH mutant is more susceptible to oxidative stresses and that the inducible expression of the thioredoxin reductase/thioredoxin genes trxB2/trxC and a gene of unknown function, Rv2466c, is regulated by sigH via expression from promoters directly recognized by SigH. We also determined that the sigH mutant is more susceptible to heat stress and that inducible expression of the heat shock genes dnaK and clpB is positively regulated by sigH. The induction of these heat shock gene promoters but not of other SigH-dependent promoters was markedly greater in response to heat versus oxidative stress, consistent with their additional regulation by a heat-labile repressor. To further understand the role of sigH in the M. tuberculosis stress response, we investigated the regulation of the stress-responsive sigma factor genes sigE and sigB. We determined that inducible expression of sigE is regulated by sigH and that basal and inducible expression of sigB is dependent on sigE and sigH. These data indicate that sigH plays a central role in a network that regulates heat and oxidative-stress responses that are likely to be important in M. tuberculosis pathogenesis.

Evaluation of T-cell responses to peptides and lipopeptides with MHC class I binding motifs derived from the amino acid sequence of the 19-kDa lipoprotein of Mycobacterium tuberculosis

Cytotoxic T-lymphocyte (CTL) epitopes on the 19-kDa lipoprotein from Mycobacterium tuberculosis were identified by the use of lipopeptides and their cytokine profile studied. Selection of candidate CTL epitopes was based on synthetic peptides derived from the amino acid sequence of the 19-kDa lipoprotein showing major histocompatibility complex class I (MHC-I) binding motifs (H-2D(b) and H-2L(d)). Their ability to up-regulate and stabilize MHC-I molecules on the mouse lymphoma cell line RMA-S was studied. Similar studies were performed with peptides, in which the anchor amino acid of the H-2D(b) MHC-I motif was replaced by alanine. Three out of five peptides with H-2D(b) or H-2L(d) binding motifs and their corresponding lipopeptides as well, up-regulated and stabilized the H-2D(b) molecules on RMA-S cells. Replacement of the anchor amino acid residues of the H-2D(b) MHC-I motif by alanine revealed that the anchor amino acid asparagine at position 5, contributed more to binding of peptide to H-2D(b) molecules than leucine at position 11. The closely related lipopeptides LP19c and LP19d, in combination with incomplete Freund's adjuvant (IFA), induced CTL responses in C57BL/6 (H-2(b)) mice. These CTLs could recognize the naturally processed antigen, i.e. the 19-kDa antigen protein produced and processed by the EX-19 cell line. The capacity of the various lipopeptides to induce CTL correlated well with the ability of the (lipo)peptide to up-regulate and to stabilize H-2D(b) molecules. Lipopeptide LP19c primed spleen cells showed a T helper type one profile after in vitro stimulation with P19c and P19d 19 kDa peptides. The approach to characterize presumptive 19-kDa CTL epitopes might lead to selection of promising CTL epitopes, which can be applied in the development of subunit tuberculosis vaccines.

Early emergence of CD8(+) T cells primed for production of type 1 cytokines in the lungs of Mycobacterium tuberculosis-infected mice

Several lines of evidence suggest that CD8 T cells are important in protection against tuberculosis. To understand the function of this cell population in the immune response against Mycobacterium tuberculosis, T cells from lungs of M. tuberculosis-infected mice were examined by flow cytometry. The kinetics of the appearance of CD8 T cells in lungs of infected mice closely paralleled that of CD4 T cells. Both CD4(+) and CD8(+) T cells displaying an activated phenotype were found in the lungs as early as 1 week postinfection. By 2 weeks, total cell numbers in the lungs had tripled and percentages of T cells were increased two- to threefold; the percentages of CD4(+) T cells were ca. twofold higher than those of CD8(+) T cells. Short-term stimulation with M. tuberculosis-infected antigen-presenting cells induced cytokine production by primed CD4(+) and CD8(+) T cells. Intracellular cytokine staining revealed that 30% +/- 5% of CD4(+) and 23% +/- 4% of CD8(+) T cells were primed for production of gamma interferon (IFN-gamma). However, a difference in in vivo IFN-gamma production by T cells was observed with approximately 12% of CD4(+) T cells and approximately 5% of CD8(+) T cells secreting cytokine in the lungs at any given time during infection. The data presented indicate that although early in infection the majority of IFN-gamma is produced by CD4(+) T cells, cytokine-producing CD8(+) T cells are readily available when triggered by the appropriate stimuli.

Mycobacterial crossreactivity of M. tuberculosis reactive T cell clones from naturally converted PPD positive healthy subjects

Mycobacterium tuberculosis reactive CD4+, CD8- T cell clones were established from six naturally converted PPD positive healthy subjects by using whole bacilli as the primary stimulation antigen in vitro. Antigen specificity of the T cell clones was mapped by testing their proliferative response against a panel of pathogenic and environmental mycobacterial species. The crossreactivity patterns obtained showed that the T cell clones distributed along a spectrum from reactivity restricted to the M. tuberculosis complex to broadly crossreactive clones recognizing all mycobacterial species tested. Two of the T cell clones were able to discriminate between M. tuberculosis and M. bovis BCG, and importantly one of these clones was exclusively specific to M. tuberculosis. All of the CD4+ T cell clones tested, displayed MHC class II restricted cytotoxicity against macrophages pulsed with M. tuberculosis. In addition, some of these clones secreted GM-CSF upon antigen stimulation. The T cell clones described here represent relevant tools to identify and characterize target antigens of the immune response against M. tuberculosis with relevance to diagnosis and subunit vaccine design.

A sequential study of the bovine tuberculin reaction

The sequential histopathological and immunocytochemical changes that characterize the tuberculin reaction were studied in 13 cattle experimentally sensitized to Mycobacterium bovis, and 14 cattle naturally infected with M. bovis. There were two distinct, temporally related patterns of morphological change that were similar for both groups of cattle. The first phase, between 6 hr and 24 hr after the intradermal injection of purified protein derivative (PPD), was characterized by a perivascular aggregation of WC1+ gamma delta T cells and neutrophils and the presence of leucocytoclastic vasculitis within the papillary dermis. The second phase of the reaction was characterized by increased numbers of infiltrating BoCD4+ cells, BoCD8+ cells and macrophages, as well as an increase in expression of the interleukin-2 (IL-2) receptor and the ACT2 antigen. Macrophages were the most numerous infiltrating leucocytes between 24 hr and 72 hr after the intradermal injection of PPD. At 72 hr, the reaction was characterized by intense perivascular cuffing with BoCD4+ cells, BoCD8+ cells and macrophages; gamma delta T cells and neutrophils were a minor component of the reaction and leucocytoclastic vasculitis was no longer observed. No B cells were detected in the dermis throughout the period of study. The increase in skin thickness was primarily because of inflammatory oedema that was contained within the area by a meshwork of fibrin deposited around the collagen bundles of the reticular dermis.

Characterization of an inhibitory seric factor from tuberculosis anergic patients that acts on non-adherent PPD reactive cells

Non-adherent cells from PPD+ tuberculosis patients (TBP PPD+) and from healthy individuals treated with whole tuberculosis anergic immune sera or with its protein A-Sepharose IgG fraction, or with sera fraction separated by PPD-Sepharose chromatography, were submitted to immunofluorescence assays. Anti-human IgG or IgM FITC-conjugate were used to reveal the assays, and results were expressed by a fluorescence percentage or fluorescence index. The presence of IgG over the surface of PPD+ non-adherent cells was detected. High fluorescence percentages were observed only in those PPD+ cells treated with whole anergic serum or with its IgG fraction. Positive fluorescence index values were obtained only in those PPD+ cells treated with anergic serum, meanwhile fluorescence index was always negative when non-bound fractions from PPD-Sepharose were used. Results suggest that non-adherent population are the cell targets for the serum inhibitory factor, which previously has been detected to inhibit antigen response in PPD reactive cells and, point out the specific behavior of this factor, since it was eliminate by PPD-Sepharose chromatography. The IgG nature of the factor was demonstrated by SDS-PAGE and immunoelectrophoresis.

The role of interleukin-12 in acquired immunity to Mycobacterium tuberculosis infection

The early phase of acquired cellular immunity to Mycobacterium tuberculosis infection is mediated by the emergence of protective CD4 T lymphocytes that secrete cytokines including interferon-gamma (IFN-gamma), a molecule which is pivotal in the expression of resistance to tuberculosis. Recent evidence demonstrates that infection with M. tuberculosis induces peripheral blood mononuclear cells to release the cytokine interleukin-12 (IL-12), a molecule that promotes the emergence of T-helper type-1 (Th1), IFN-gamma-producing T cells. We demonstrate here that IL-12 mRNA expression was induced by M. tuberculosis infection both in vivo and in vitro and that exogenous administration of IL-12 to mice transiently resulted in increased resistance to the infection. IL-12 also increased the production of IFN-gamma by both splenocytes derived from infected animals treated in vivo and by antigen-stimulated CD4 cells from untreated infected animals, with maximal effects at times associated with the expansion of antigen-specific CD4 T cells in vivo. In the absence of a T-cell response, as seen in SCID mice or nude mice, IL-12 only slightly augmented the moderate bacteriostatic capacity of these immunocompromised mice. Neutralization of IL-12 by specific monoclonal antibodies resulted in a reduction in granuloma integrity and slowing of the capacity of the animal to control bacterial growth.

Infection of Mycobacterium bovis bacillus Calmette-Guérin in antibody-mediated gamma delta T-cell-depleted mice

To evaluate the hypothesis that gamma delta T cells participate in protective immunity against mycobacterial infection, we depleted gamma delta T cells from mice by administration of anti-T-cell receptor (TCR)gamma delta monoclonal antibody (mAb) and analysed protection against Mycobacterium bovis bacillus Calmette-Guérin (BCG). The gamma delta T-cell-depleted mice did not show any exaggerated bacterial multiplication compared with control mice. In contrast, alpha beta T-cell-depleted mice, which were administrated anti-TCR alpha beta mAb before BCG infection, showed a depressed protective immunity. These results suggest that gamma delta T cells are not essential for coping with a primary BCG infection.

A Salmonella enteritidis 11RX pilin induces strong T-lymphocyte responses

Our previous work, using proteins fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to define antigens of Salmonella enteritidis 11RX able to stimulate T cells from S. enteritidis 11RX-primed (BALB/c x C57BL/6)F1 mice, had indicated the presence of a major antigenic determinant of 14 to 18 kDa (H.-M. Vordermeier and I. Kotlarski, Immunol. Cell. Biol. 68:299-305, 1990). The 14-kDa size is similar to that of the monomeric units of one of the fimbrial structures, SEF14, produced by a human enteropathogen, S. enteritidis 27655 (J. Feutrier, W. W. Kay, and T. J. Trust, J. Bacteriol. 168:221-227, 1986). Here we present data which indicate that S. enteritidis 11RX also produces this protein and that it is able to elicit delayed-type hypersensitivity reactions in S. enteritidis 11RX-primed animals and to stimulate in vitro proliferation of, and cytokine release from, T cells obtained from these animals, implying that this fimbrial protein is likely to be an important immunogen of S. enteritidis. The protein was purified to homogeneity and is free from contamination with lipopolysaccharide. Standard immunoblot analysis with unabsorbed S. enteritidis 11RX antiserum and antiserum absorbed with Salmonella typhimurium C5 and various strains of Escherichia coli, as well as a panel of anti-14-kDa-protein monoclonal antibodies, suggests that this fimbrial protein is not the common antigen expressed by a number of organisms belonging to the family Enterobacteriaceae. Immunogold electron microscopy with one of these monoclonal antibodies confirms that the 14-kDa protein and SEF14 are identical.

Cellular and humoral immune responses of cattle to purified Mycobacterium bovis antigens

Cellular responses to several purified antigens of Mycobacterium bovis were examined in experimentally infected cattle over a period of 36 months, using in vitro cellular proliferation and interferon-gamma assays. These antigens (12, 19, 22a, b, 24, 25, 30, 32, 39, 65 and 70 kDa) included the majority of M. bovis protein antigens described to date and are highly homologous to those purified from M. tuberculosis. Cellular responses were examined at 3-month time intervals during the 36-month course of infection. All purified antigens induced cellular immune responses in the infected animals. The onset and magnitude of response to individual antigens varied among the animals. At any specific time during the period of infection one or more antigens appeared to be immunodominant but the immunodominance profile changed as the infection progressed. Humoral immune responses were low or absent in the first half of the infection period, but increased substantially for some of the antigens during the second half. Variation was observed among the different animals as to which antigens they recognized.

In vivo depletion of CD4 and CD8 T lymphocytes impairs Mycobacterium w vaccine-induced protection against M. tuberculosis in mice

In the present study we sought to determine the relative role of CD4 and CD8 T cells in Mycobacterium w-induced protective immunity against tuberculosis of mice by in vivo depletion with specific monoclonal antibodies (mAb). Mice were immunized first with M.w, 4 weeks later treated with anti-CD4, anti-CD8 or a combination of both mAb and subsequently infected with M. tuberculosis H37Rv i.v. Numbers of colony-forming units in animals depleted of CD4 T cells, CD8 T cells or both T cell populations were significantly higher than those in control mice receiving irrelevant mAb or no mAb. Cytokine production by T cell subsets was also determined by culturing the cells remaining after in vivo depletion in the presence or absence of mycobacterial antigens. CD8 (CD4 depleted) T cells produced lower levels of interferon-gamma than CD4 (CD8 depleted) T cells. These data suggest that both CD4 and CD8 T cells participate in resistance against tuberculosis induced by vaccination with M.w.

Tuberculosis--immunopathogenesis and therapy

Infection with Mycobacterium tuberculosis (TB) has returned to the forefront of public and medical concern because of the recent sharp increase in the number of cases. Major strides have been made in understanding the pathogenesis of TB, and some of these basic advances are being applied clinically. This review focuses on current concepts of the host response to TB, the changing epidemiology of TB, and optimal treatment strategies.

M. tuberculosis-complex specific T-cell stimulation and DTH reactions induced with a peptide from the 38-kDa protein

An immunodominant T-cell-stimulatory epitope located near the carboxy terminus of the 38-kDa antigen from M. tuberculosis (38.G, residues 350-369) was found to be M. tuberculosis-complex specific. This was demonstrated by the presence of proliferative and delayed type hypersensitivity (DTH) responses in mice immunized with Mycobacterium tuberculosis and Mycobacterium bovis BCG, whereas mice immunized with M. avium or other non-tuberculous species of mycobacteria showed no such responses. Peptide 38.G stimulated the proliferation of peripheral blood lymphocytes from healthy purified protein derivative (PPD)-positive individuals but not from PPD-negative individuals. It also elicited DTH responses in M. tuberculosis sensitized mice and in PPD-positive healthy human volunteers. Peptide 38.G could therefore prove to be an important component in any new molecularly defined reagent used in the immunodiagnosis of tuberculous infection.

In vitro characterization of T cells from Mycobacterium w-vaccinated mice

Tuberculosis caused by the intracellular bacterial pathogen Mycobacterium tuberculosis still represents a major health problem, and its effective control would best be accomplished by active vaccination. Although vaccination with M. bovis BCG has proven highly effective in certain parts of the world, in several developing countries it has been found to confer only marginal protection. Hence, novel vaccination strategies are warranted. Mycobacterium w is a saprophytic cultivable mycobacterium which shares several antigens with M. tuberculosis. In the murine system, vaccination with killed M. w was found to protect against subsequent tuberculosis. In order to characterize the responsible immune mechanisms more precisely, mice were vaccinated with killed M. w and T cells restimulated in vitro with mycobacterial antigens. These T cells produced interleukin 2 and gamma interferon but no detectable interleukin 4 and interleukin 5. Killed M. w induced significantly stronger T-cell responses than killed M. tuberculosis, and both vaccination regimes were markedly improved by administration in a mild adjuvant, i.e., the Ribi adjuvant containing trehalose dimycolate, monophosphoryl lipid A, and mycobacterial cell wall skeleton. Our data suggest that M. w-induced immunity against M. tuberculosis rests primarily on TH1 cells, which are thought to be of major relevance for acquired antituberculosis resistance. Our study therefore provides a further step toward the identification of a novel tuberculosis vaccine.

Tuberculosis in domesticated red deer: comparison of purified protein derivative and the specific protein MPB70 for in vitro diagnosis

The use of a Mycobacterium bovis-specific protein, mycobacterial protein bovis 70 (MPB70), was compared with complex, M bovis-derived purified protein derivative (bovine PPD), for its ability to improve the diagnostic precision of in vitro assays for tuberculosis in farmed deer. A combination of lymphocyte transformation and enzyme-linked immunosorbent assay (ELISA) was used to differentiate between specific M bovis reactivity and crossreactivity due to sensitisation with saprophytic mycobacteria such as Mycobacterium avium. In the lymphocyte transformation assay the response of mononuclear cells, from red deer, to MPB70 was found to be more specific, but less sensitive, as an indicator of infection by M bovis when compared with the complex antigen bovine PPD. When used in conjunction with bovine PPD alone, MPB70 was found to increase the specificity of the ELISA in diagnosing animals with disease.

Human immune response to Mycobacterium tuberculosis antigens

Little is known about the immunodominant or protective antigens of Mycobacterium tuberculosis in humans. Cell-mediated immunity is necessary for protection, and healthy tuberculin-positive individuals are relatively resistant to exogenous reinfection. We compared the targets of the cell-mediated immune response in healthy tuberculin-positive individuals to those of tuberculosis patients and tuberculin-negative persons. By using T-cell Western blotting (immunoblotting) of nitrocellulose-bound M. tuberculosis culture filtrate, peaks of T-cell blastogenic activity were identified in the healthy tuberculin reactors at 30, 37, 44, 57, 64, 71 and 88 kDa. Three of these fractions (30, 64, and 71 kDa) coincided with previously characterized proteins: antigen 6/alpha antigen, HSP60, and HSP70, respectively. The blastogenic responses to purified M. tuberculosis antigen 6/alpha antigen and BCG HSP60 were assessed. When cultured with purified antigen 6/alpha antigen, lymphocytes of healthy tuberculin reactors demonstrated greater [3H]thymidine incorporation than either healthy tuberculin-negative controls or tuberculous patients (8,113 +/- 1,939 delta cpm versus 645 +/- 425 delta cpm and 1,019 +/- 710 delta cpm, respectively; P less than 0.01). Healthy reactors also responded to HSP60, although to a lesser degree than antigen 6/alpha antigen (4,276 +/- 1,095 delta cpm; P less than 0.05). Partially purified HSP70 bound to nitrocellulose paper elicited a significant lymphocyte blastogenic response in two of six of the tuberculous patients but in none of the eight healthy tuberculin reactors. Lymphocytes of none of five tuberculin-negative controls responded to recombinant antigens at 14 or 19 kDa or to HSP70. Antibody reactivity generally was inversely correlated with blastogenic response: tuberculous sera had high titer antibody to M. tuberculosis culture filtrate in a range from 35 to 180 kDa. This is the first systematic evaluation of the human response to a panel of native and recombinant antigens in healthy tuberculin reactors and tuberculous patients. Antigens which stimulated prominent lymphocyte blastogenic responses were identified in seven fractions on T-cell Western blot analysis. Two of these may represent previously characterized proteins; the others may contain immunodominant proteins that will require further characterization.

Legionella pneumophila htpAB heat shock operon: nucleotide sequence and expression of the 60-kilodalton antigen in L. pneumophila-infected HeLa cells

A 60-kilodalton (kDa) immunodominant antigen of Legionella pneumophila is a heat shock protein (HSP) of the GroEL class of HSPs. The gene (htpB) coding the 60-kDa protein was localized to a 3.2-kilobase DNA fragment of L. pneumophila cloned into pUC19 (pSH16) (P. S. Hoffman, C. A. Butler, and F. D. Quinn, Infect. Immun. 57:1731-1739, 1989). The nucleotide sequence of the DNA fragment cloned into M13 confirmed two open reading frames, htpA and htpB, that code for proteins of 96 and 548 amino acids, respectively. A consensus heat shock promoter sequence upstream of the start of htpA was identified, and no obvious promoter sequences were detected upstream of htpB. Amino acid sequence comparison studies revealed that the L. pneumophila HtpB protein exhibited 76% homology with the 65-kDa protein of Mycobacterium tuberculosis and 85% homology with both GroEL of Escherichia coli and HtpB of Coxiella burnetii. A comparison of the amino acid sequences among these proteins revealed several regions of nearly absolute sequence conservation, with the variable regions occurring in common areas. The purified L. pneumophila 60-kDa protein was antigenic for human T lymphocytes. Indirect fluorescent antibody studies indicated that the 60-kDa protein may be located in the periplasm or expressed on the surface by intracellular bacteria, suggesting that a stress-related mechanism may be involved in the expression of this immunodominant antigen.

Partial purification and characterization of low molecular weight antigens of Salmonella enteritidis 11RX

Sephadex G100 chromatography and preparative sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) using 16% polyacrylamide gels were used for the partial purification of 16-18 kDa proteins able to stimulate Salmonella enteritidis 11RX-primed T cells of (BALB/c x C57BL/6J)F1 mice. A soluble antigen (Ag) extract of S. enteritidis 11RX (s11RX) was used as the starting material for purification for two reasons. First, s11RX had been previously shown to induce in vitro proliferation of Salmonella-primed T cells; second, initial analysis of SDS-PAGE fractionated s11RX Ag using the 'T cell western blot' technique indicated that T cell stimulatory activity was located only in the 16-18 kDa region. The partially purified antigens were able to elicit delayed-type hypersensitivity reactions in vivo, and stimulated in vitro proliferation and interleukin-2 release from 11RX-primed T cells and T cell lines and clones derived from these cells, indicating that they are major antigenic determinants of S. enteritidis 11RX. Testing of 16-18 kDa proteins of several other bacteria indicated that these antigens may be 'common' and expressed by a number of organisms belonging to the Enterobacteriaceae.

Identification of antigens which stimulate T lymphocytes of Salmonella enteritidis 11RX immunized mice

The technique of using sodium dodecylsulfate-polyacrylamide gel electrophoresis fractionated antigens (Ag) transferred to nitrocellulose filters was adopted to analyse T cell responses to Salmonella enteritidis 11RX Ag. Employing in vitro proliferation assays with T cells from S. enteritidis 11RX-primed (BALB/c x C57BL/6J)F1 mice as the measure of T cell stimulation, we have identified Ag able to stimulate T cells in the regions containing 16, 24, 34 and 50-60 kDa proteins, with dominant Ag activity at about 16 kDa. These results were confirmed with long-term, Ag-specific L3T4+ T cell lines which responded to molecules in the same four Mr regions, suggesting that no selection by a single antigenic determinant had occurred during more than 3 months of in vitro culture, or that all the molecules which were stimulatory shared at least one antigenic determinant. Because the seven clones we examined responded only to 16 kDa molecules, the former alternative is the more likely. Standard immunoblot analysis indicated that these Ag also act as major B cell stimulating determinants. T cells of BALB/c mice, which are 5-10 times more resistant to S. enteritidis 11RX than C57BL/6J mice, showed the same pattern of reactivity as F1 mice whereas the major antigenic region for T cells of C57BL/6J mice was located between 50 and 60 kDa.

Presentation of Salmonella antigens by peritoneal cells of normal and Salmonella-infected mice

A comparison of the ability of normal peritoneal cells (PC) and those harvested from mice 1-3 days after intraperitoneal immunization with live Salmonella enteritidis 11RX (11RX) to present antigen to 11RX-primed T cells was made using formalin-killed 11RX and a soluble 11RX antigen extract as antigens. Unfractionated PC and the adherent and non-adherent PC populations were analysed separately and the effects of the lysosomal function-impairing drug chloroquine and the fixative paraformaldehyde, used before or after antigen-pulsing, were also determined. The results presented indicate that immunization with live 11RX did not induce any detectable modulation of APC function which could account for the ability of live 11RX to induce cell-mediated immune responses involving Lyt 2+ T cells.

Francisella tularensis-specific T-cell clones are human leukocyte antigen class II restricted, secrete interleukin-2 and gamma interferon, and induce immunoglobulin production

T-cell clones (TLC) were established from a Francisella tularensis-vaccinated subject in order to study the cells responsive for cell-mediated immunity against F. tularensis. All the clones were human leukocyte antigen (HLA) class II restricted to one of the HLA-DR specificities of the original donor. The TLC cells were CD4+ and produced interleukin-2 and gamma interferon after stimulation with specific antigen. Seven of the eight clones tested assisted in the production of immunoglobulin G (IgG), IgA, and IgM antibodies.

Molecular cloning and expression of a T-cell stimulating membrane protein of Francisella tularensis

The isolation and expression in Escherichia coli of a gene encoding a T-cell stimulating 17 kiloDalton (kDa) membrane protein of Francisella tularensis is described. A genomic library of DNA from the live vaccine strain LVS of F. tularensis was constructed in the E. coli expression vector phage lambda gt11. The library was probed with antibodies directed against the 17 kDa protein. One recombinant phage was isolated, containing a 2.8 kilobase (kb) DNA insert. The insert was cleaved and a resulting 1.2 kb fragment was found to express the 17 kDa protein. The 1.2 kb fragment was inserted in the high copy number plasmid pUC18 and expressed in E. coli. Membrane preparations of these bacteria induced a response in T cells from F. tularensis-primed individuals but not in T cells from non-primed individuals. The cloned gene may become useful in studies on host interaction with F. tularensis and enable a precise identification of bacterial structures involved in the T-cell response.

Cloning and temperature-dependent expression in Escherichia coli of a Legionella pneumophila gene coding for a genus-common 60-kilodalton antigen

All Legionella species express a 60-kilodalton (kDa) protein which contains a genus-specific epitope recognized by murine monoclonal antibody GW2X4B8B2H6. A genomic cosmid library of Legionella pneumophila chromosomal DNA was constructed in pHC79 and screened for 60-kDa antigen-expressing clones with the monoclonal antibody. A 3.2-kilobase EcoRI fragment from cosmid 14B11 expressing a 60-kDa protein was subcloned into pUC19 (pSH16), and deletion of a 1.2-kilobase HindIII fragment (pSH16A) generated a 33-kDa truncated polypeptide no longer reactive with the monoclonal antibody. Southern blot analysis of chromosomal DNA from selected Legionella species restricted with EcoRI and probed with the 1.2-kilobase fragment coding for the carboxyl region of the protein revealed DNA homology which was not observed with DNA from Escherichia coli. Maxicell analysis of pSH16 identified a second polypeptide of approximately 15 kDa expressed from a gene (htpA) upstream of the gene coding the 60-kDa protein (htpB). Both proteins were preferentially synthesized by L. pneumophila following heat shock (temperature shift from 25 to 42 degrees C), and under steady-state growth conditions the relative level of 60-kDa protein was unaffected by temperature. In E. coli, expression of a 60-kDa protein from pSH16 also increased following heat shock (25 to 42 degrees C), but under steady-state conditions expression was temperature dependent. Temperature-dependent expression from pSH16 was not observed in an rpoH (htpR) mutant strain of E. coli. The Legionella 60-kDa protein appears to be a heat shock protein which shares cross-reactive epitopes with the GroEL homolog of E. coli. In addition, a region of htpB encoding the 27-kDa carboxyl portion of the protein containing the monoclonal antibody-reactive epitope also contains DNA sequences unique to and conserved within the genus.

The generation of guinea pig T-cell lines reactive to antigens from Mycobacterium tuberculosis. Selected lines induce erythematous skin reactions

We describe methods for the development and partial characterization of antigen-specific T-cell lines from the guinea pig, which is the classical experimental animal in tuberculosis research. T cells were obtained from strain 2 guinea pigs immunized with BCG vaccine or with killed Mycobacterium tuberculosis in oil. T-cell lines were obtained from limited dilution cloning of antigen-stimulated, blast-enriched lymphocyte cultures. The lines were grown with weekly reseedings in the alternating absence and presence of mycobacterial antigen. Antigen reactivity of the cell lines was studied with lymphocyte stimulation tests. With these methods we have consistently obtained antigen-reactive cell lines. When injected in small numbers intradermally in the presence of antigen in syngeneic guinea pigs, some of these cell lines gave rise to antigen-specific erythematous tuberculin-like skin reactions. The skin reactions, which were usually without induration, were most pronounced after 24 h. Histological examinations of skin undergoing such reactions showed that the erythemas were not accompanied by mononuclear infiltrations. We expect that transfer experiments with guinea pig T-cell lines will prove useful tools in the analysis of the contribution of defined mycobacterial antigen preparations to tuberculosis immunity.

Induction of nonspecific acquired resistance and delayed-type hypersensitivity, but not specific acquired resistance in mice inoculated with killed mycobacterial vaccines

A number of nonliving mycobacterial preparations were tested in vivo for their capacity to generate various relevant parameters of cellular immunity. All preparations tested had some detectable activity in raising resistance to challenge with Mycobacterium tuberculosis or with Listeria monocytogenes and in conferring the ability to mount a delayed-type hypersensitivity response to tuberculin. This report presents the first evidence, however, that none of these preparations were able to generate protective T cells capable of adoptive immunization against virulent tuberculosis. These data are discussed in terms of the use of these preparations in generating M. tuberculosis-reactive T-cell lines and the application of these lines in the continuing search for an improved vaccine against tuberculosis.

Evidence for a biphasic memory T-cell response to high dose BCG vaccination in mice

Memory immunity in mice to BCG vaccination is mediated by Thy-1.2+ L3T4+ Lyt-2- cyclophosphamide-resistant T-lymphocytes. The time required for the emergence of acquired memory immunity was inversely proportional to the BCG inoculum size, although the level of memory expressed, once established, was equivalent regardless of the original dose of BCG administered. In mice given a high intravenous dose (10(8)) of BCG, an apparently biphasic memory response was observed, initially peaking on day 15-20, then declining for 10 days or so before increasing again to maximal levels between day 30 and 60 of the infection. This trough in resistance was not due to an active immunosuppressive mechanism; instead, it is suggested that it represents an initial loss or consumption of memory T-cells generated early during the infection which are stimulated to give rise to a state of active immunity as a result of the persisting high mycobacterial load.

Prediction and identification of an HLA-DR-restricted T cell determinant in the 19-kDa protein of Mycobacterium tuberculosis

An allele-specific motif has been identified in the sequence of several peptides which are recognized by T cells in association with HLA-DR1. In order to test the predictive values of such a motif we analyzed the 19-kDa antigen from Mycobacterium tuberculosis and identified a sequence containing a pattern characteristic of DR1 restriction. Peripheral blood mononuclear leukocytes from every DR1 and 4 individual tested responded to the corresponding synthetic peptide. Nine other donors, constituting seven different DR alleles, failed to recognize this sequence. Recognition of the peptide in association with DR1 and DR4 was confirmed using T cell clones and transfected murine L cell lines expressing DR molecules.

Stress proteins are immune targets in leprosy and tuberculosis

To understand the immune response to infection by tuberculosis and leprosy bacilli and to develop improved vaccines, the nature of antigens that are involved in humoral and cell-mediated immunity was investigated. We have determined that five immunodominant protein antigens under study are homologues of stress proteins. This finding and observations with other pathogens suggest that infectious agents may respond to the host environment by producing stress proteins and that these proteins can be important immune targets. We postulate that abundant and highly conserved stress proteins may have "immunoprophylactic" potential for a broad spectrum of human pathogens.

Heterogeneity of helper/inducer T lymphocytes. I. Lymphokine production and lymphokine responsiveness

Antigen-specific, Ia-restricted helper/inducer T lymphocytes consist of subsets that can be distinguished by lymphokine secretion. One, called Th1, secretes IL-2 and the other, termed Th2, produces BSF-1/IL-4 in response to stimulation by lectin or antigen receptor signals, and each uses the respective lymphokine as its autocrine growth factor. Cloned lines representing Th2 cells proliferate in response to both IL-2 and their autocrine lymphokine, BSF-1/IL-4, but this proliferation is dependent on the synergistic costimulator activity of the monokine, IL-1. In contrast, Th1 clones proliferate only in response to IL-2, are unresponsive to BSF-1/IL-4, and their growth is unaffected by IL-1. These response patterns are not attributable to variations in culture conditions but apparently reflect intrinsic properties of the two T cell subsets. Moreover, the unresponsiveness of Th1 cells to BSF-1/IL-4 may be related to lower levels of expression of surface receptors for this lymphokine. These results may explain the observed heterogeneity among bulk populations of T cells in terms of lymphokine responsiveness and requirement for accessory factors (costimulators). In addition, our findings suggest that IL-2, unlike BSF-1/IL-4, is a fully competent growth factor that is potentially involved in antigen-independent expansion of bystander T cells present at sites of immune stimulation.