Immunogenicity of Mycobacterium tuberculosis antigens in Mycobacterium bovis BCG-vaccinated and M. bovis-infected cattle

The development of novel vaccine strategies supplementing Mycobacterium bovis BCG (BCG) constitutes an urgent research challenge. To identify potential subunit vaccine candidates, we have tested a series of eight recently identified Mycobacterium tuberculosis antigens in M. bovis-infected and BCG-vaccinated cattle. These antigens were characterized on the basis of their ability to induce in vitro gamma interferon responses in infected or BCG-vaccinated calves. We were able to establish a hierarchy of these antigens based on how frequently they were recognized in both groups of animals. In particular, we were able to prioritize frequently recognized proteins like Rv0287, Rv1174, and Rv1196 for future evaluation as subunit vaccines to be used in BCG-protein heterologous prime-boost vaccination scenarios. In addition, the antigen most dominantly recognized in M. bovis-infected cattle in this study, Rv3616c, was significantly less frequently recognized by BCG vaccinees and could be a target to improve BCG, for example, by increasing its secretion, in a recombinant BCG vaccine.

Evaluation of DPPD, a single recombinant Mycobacterium tuberculosis protein as an alternative antigen for the Mantoux test

Although the tuberculin test has aided in the diagnosis of tuberculosis for more than 85 years, its interpretation is difficult particularly because sensitization with non-tuberculous mycobacteria leads to false positive tests. Using the guinea pig model of tuberculosis, we have recently described a recombinant antigen (DPPD) that could circumvent this problem. The DPPD gene is unique to the M. tuberculosis complex organisms and is absent in the organisms representative of all other members of the Mycobacterium genus. Moreover, DPPD induced strong DTH in 100% of the guinea pigs infected with M. tuberculosis and in none of the guinea pigs immunized with nine different species of Mycobacterium. Here we present results of a clinical investigation using DPPD. Mantoux test using both PPD and DPPD was initially performed in 26 patients with confirmed pulmonary tuberculosis and in 25 healthy PPD negative individuals. The results indicated that both PPD and DPPD elicited DTH in 24 out of the 26 patients. No DTH was observed in any of the PPD negative individuals. In addition, a small clinical trial was performed in a population of 270 clinically healthy and randomly selected individuals. DPPD produced a bimodal histogram of skin reaction size and PPD produced a skewed histogram. Because the DPPD gene is not present in non-tuberculous bacilli, these results suggest that this molecule can be an additional tool for a more specific diagnosis of tuberculosis.

Potent stimulation of the innate immune system by a Leishmania brasiliensis recombinant protein

The interaction of the innate immune system with the microbial world involves primarily two sets of molecules generally known as microbial pattern recognition receptors and microbial pattern recognition molecules, respectively. Examples of the former are the Toll receptors present particularly in macrophages and dendritic cells. Conversely, the microbial pattern recognition molecules are conserved protist homopolymers, such as bacterial lipopolysaccharides, lipoteichoic acids, peptidoglycans, glucans, mannans, unmethylated bacterial DNA, and double-strand viral RNA. However, for protists that lack most of these molecules, such as protozoans, the innate immune system must have evolved receptors that recognize other groups of microbial molecules. Here we present evidence that a highly purified protein encoded by a Leishmania brasiliensis gene may be one such molecule. This recombinant leishmanial molecule, a homologue of eukaryotic ribosomal elongation and initiation factor 4a (LeIF), strongly stimulates spleen cells from severe combined immunodeficient (SCID) mice to produce interleukin-12 (IL-12), IL-18, and high levels of gamma interferon. In addition, LeIF potentiates the cytotoxic activity of the NK cells of these animals. Because LeIF is a conserved molecule and because SCID mice lack T and B lymphocytes but have a normal innate immune system (normal reticuloendothelial system and NK cells), these results suggest that proteins may also be included as microbial pattern recognition molecules. The nature of the receptor involved in this innate recognition is unknown. However, it is possible to exclude the Toll receptor Tlr4 as a putative LeIF receptor because the gene encoding this receptor is defective in C3H/HeJ mice, the mouse strain used in the present studies.

Serological expression cloning and immunological evaluation of MTB48, a novel Mycobacterium tuberculosis antigen

Improved diagnostics are needed for the detection of Mycobacterium tuberculosis, especially for patients with smear-negative disease. To address this problem, we have screened M. tuberculosis (H37Rv and Erdman strains) genomic expression libraries with pooled sera from patients with extrapulmonary disease and with sera from patients with elevated reactivity with M. tuberculosis lysate. Both serum pools were reactive with clones expressing a recombinant protein referred to here as MTB48. The genomic sequence of the resulting clones was identical to that of the M. tuberculosis H37Rv isolate and showed 99% identity to the Mycobacterium bovis and M. bovis BCG isolate sequences. The genomic location of this sequence is 826 bp upstream of a region containing the esat-6 gene that is deleted in the M. bovis BCG isolate. The mtb48 1,380-bp open reading frame encodes a predicted 47.6-kDa polypeptide with no known function. Southern and Western blot analyses indicate that this sequence is present in a single copy and is conserved in the M. tuberculosis and M. bovis isolates tested but not in other mycobacterial species tested, including Mycobacterium leprae and Mycobacterium avium. In addition, the native protein was detected in the cytoplasm, as was a processed form that was also shed into the medium during culture. Serological analysis of recombinant MTB48 and the M. tuberculosis 38-kDa antigen with a panel of patient and control sera indicates that the inclusion of recombinant MTB48 in a prototype serodiagnostic test increases assay sensitivity for M. tuberculosis infection when it is combined with other known immunodominant antigens, such as the 38-kDa antigen.

Assessment of the serodiagnostic potential of nine novel proteins from Mycobacterium tuberculosis

To identify antigens that would improve the accuracy of serological diagnosis of active tuberculosis, we cloned the genes encoding nine potentially immunogenic secreted or surface-associated proteins of Mycobacterium tuberculosis. Recombinant proteins were reacted with sera from HIV-negative individuals with extrapulmonary tuberculosis (EP-TB) or HIV-positive individuals with pulmonary tuberculosis (TBH). Specific and high level antibody responses were obtained for four recombinant proteins, of which antigen GST-822 was recognized by 60% of EP-TB and 42% of TBH and antigen MBP-506 was recognized by 45% of EP-TB and 61% of TBH. These results suggest that these proteins are strong candidates as subunits in a polyvalent serodiagnostic test.

The potency and durability of DNA- and protein-based vaccines against Leishmania major evaluated using low-dose, intradermal challenge

DNA- and protein- based vaccines against cutaneous leishmaniasis due to Leishmania major were evaluated using a challenge model that more closely reproduces the pathology and immunity associated with sand fly-transmitted infection. C57BL/6 mice were vaccinated s.c. with a mixture of plasmid DNAs encoding the Leishmania Ags LACK, LmSTI1, and TSA (AgDNA), or with autoclaved L. major promastigotes (ALM) plus rIL-12, and the mice were challenged by inoculation of 100 metacyclic promastigotes in the ear dermis. When challenged at 2 wk postvaccination, mice receiving AgDNA or ALM/rIL-12 were completely protected against the development of dermal lesions, and both groups had a 100-fold reduction in peak dermal parasite loads compared with controls. When challenged at 12 wk, mice vaccinated with ALM/rIL-12 maintained partial protection against dermal lesions and their parasite loads were no longer significantly reduced, whereas the mice vaccinated with AgDNA remained completely protected and had a 1000-fold reduction in dermal parasite loads. Mice vaccinated with AgDNA also harbored few, if any, parasites in the skin during the chronic phase, and their ability to transmit L. major to vector sand flies was completely abrogated. The durable protection in mice vaccinated with AgDNA was associated with the recruitment of both CD8(+) and CD4(+) T cells to the site of intradermal challenge and with IFN-gamma production by CD8(+) T cells in lymph nodes draining the challenge site. These data suggest that under conditions of natural challenge, DNA vaccination has the capacity to confer complete protection against cutaneous leishmaniasis and to prevent the establishment of infection reservoirs.

WT1-specific serum antibodies in patients with leukemia

WT1 is an oncogenic protein expressed by the Wilms' tumor gene and overexpressed in the majority of acute myelogenous leukemias (AMLs) and chronic myelogenous leukemias (CMLs). The current study analyzed the sera of patients with AML and CML for the presence of antibodies to full-length and truncated WT1 proteins. Sixteen of 63 patients (25%) with AML had serum antibodies reactive with WT1/full-length protein. Serum antibodies from all 16 were also reactive with WT1/NH2-terminal protein. By marked contrast, only 2 had reactivity to WT1/COOH-terminal protein. Thus, the level of immunological tolerance to the COOH terminus may be higher than to the NH2 terminus. The WT1/COOH-terminal protein contains four zinc finger domains with homology to other self-proteins. By implication, these homologies may be related to the increased immunological tolerance. Results in patients with CML were similar with antibodies reactive to WT1/full-length protein detectable in serum of 15 of 81 patients (19%). Antibodies reactive with WT1/NH2-terminal protein were present in the serum of all 15, whereas antibodies reactive with WT1/COOH-terminal protein were present in only 3. By contrast to results in leukemia patients, antibodies reactive with WT1/full-length protein were detected in only 2 of 96 normal individuals. The greater incidence of antibody in leukemia patients provides strong evidence that immunization to the WT1 protein occurred as a result of patients bearing malignancy that expresses WT1. These data provide further stimulus to test therapeutic vaccines directed against WT1 with increased expectation that the vaccines will be able to elicit and/or boost an immune response to WT1.

T cell expression cloning of a Mycobacterium tuberculosis gene encoding a protective antigen associated with the early control of infection

Infection of C57BL/6 mice with Mycobacterium tuberculosis results in the development of a progressive disease during the first 2 wk after challenge. Thereafter, the disease is controlled by the emergence of protective T cells. We have used this infection model in conjunction with direct T cell expression cloning to identify Ags involved with the early control of the disease. A protective M. tuberculosis-specific CD4 T cell line derived from mice at 3 wk postchallenge was used to directly screen an M. tuberculosis genomic expression library. This screen resulted in the identification of a genomic clone comprising two putative adjacent genes with predicted open reading frames of 10 and 41 kDa, MTB10 and MTB41, respectively (the products of Rv0916c and Rv0915c, respectively, in the TubercuList H37Rv database). MTB10 and MTB41 belong to the PE and PPE family of proteins recently identified to comprise 10% of the M. tuberculosis genome. Evaluation of the recombinant proteins revealed that MTB41, but not MTB10, is the Ag recognized by the cell line and by M. tuberculosis-sensitized human PBMC. Moreover, C57BL/6 mice immunized with MTB41 DNA developed both CD4- (predominantly Th1) and CD8-specific T cell responses to rMTB41 protein. More importantly, immunization of C57BL/6 mice with MTB41 DNA induced protection against infection with M. tuberculosis comparable to that induced by bacillus Calmette-Guérin. Thus, the use of a proven protective T cell line in conjunction with the T cell expression cloning approach resulted in the identification of a candidate Ag for a subunit vaccine against tuberculosis.

Molecular and immunological characterization of Mycobacterium tuberculosis CFP-10, an immunodiagnostic antigen missing in Mycobacterium bovis BCG

In order to identify antigens that may be used in the serodiagnosis of active tuberculosis (TB), we screened a Mycobacterium tuberculosis genomic expression library with a pool of sera from patients diagnosed with active pulmonary TB. The sera used lacked reactivity with a recombinant form of the M. tuberculosis 38-kDa antigen (r38kDa), and the goal was to identify antigens that might complement r38kDa in a serodiagnostic assay. Utilizing this strategy, we identified a gene, previously designated lhp, which encodes a 100-amino-acid protein referred to as culture filtrate protein 10 (CFP-10). The lhp gene is located directly upstream of esat-6, within a region missing in M. bovis BCG. Immunoblot analysis demonstrated that CFP-10 is present in M. tuberculosis CFP, indicating that it is likely a secreted or shed antigen. Purified recombinant CFP-10 (rCFP-10) was shown to be capable of detecting specific antibody in a percentage of TB patients that lack reactivity with r38kDa, most notably in smear-negative cases, where sensitivity was increased from 21% for r38kDa alone to 40% with the inclusion of rCFP-10. In smear-positive patient sera, sensitivity was increased from 49% for r38kDa alone to 58% with the inclusion of rCFP-10. In addition, rCFP-10 was shown to be a potent T-cell antigen, eliciting proliferative responses and gamma interferon production from peripheral blood mononuclear cells in 70% of purified protein derivative-positive individuals without evident disease. The responses to this antigen argue for the inclusion of rCFP-10 in a polyvalent serodiagnostic test for detection of active TB infection. rCFP-10 could also contribute to the development of a recombinant T-cell diagnostic test capable of detecting exposure to M. tuberculosis.

Cloning of a Mycobacterium tuberculosis gene encoding a purifed protein derivative protein that elicits strong tuberculosis-specific delayed-type hypersensitivity

The purified protein derivative (PPD) skin test has been used for the diagnosis of tuberculosis for more than 75 years. However, the test lacks specificity because all mycobacteria share antigens present in PPD. Therefore, sensitization with nontuberculous pathogenic or with environmental nonpathogenic mycobacteria can lead to positive skin tests. This communication describes a novel PPD protein present only in tuberculous complex mycobacteria. A recombinant protein was obtained and named DPPD on the basis of the first 4 amino acids of its N-terminus sequence. DPPD elicited delayed-type hypersensitivity (DTH) in 100% of Mycobacterium tuberculosis-infected guinea pigs but in no animals sensitized with several organisms representative of all members of the Mycobacterium genus. Preliminary results indicate that DPPD induces strong and specific DTH in humans. This work points to the definition of a single recombinant M. tuberculosis protein that may be an alternative to the PPD test.

Expression cloning of an immunodominant family of Mycobacterium tuberculosis antigens using human CD4(+) T cells

Development of a subunit vaccine for Mycobacterium tuberculosis (Mtb) is likely to be dependent on the identification of T cell antigens that induce strong proliferation and interferon gamma production from healthy purified protein derivative (PPD)(+) donors. We have developed a sensitive and rapid technique for screening an Mtb genomic library expressed in Escherichia coli using Mtb-specific CD4(+) T cells. Using this technique, we identified a family of highly related Mtb antigens. The gene of one family member encodes a 9.9-kD antigen, termed Mtb9.9A. Recombinant Mtb9.9A protein, expressed and purified from E. coli, elicited strong T cell proliferation and IFN-gamma production by peripheral blood mononuclear cells from PPD(+) but not PPD(-) individuals. Southern blot analysis and examination of the Mtb genome sequence revealed a family of highly related genes. A T cell line from a PPD(+) donor that failed to react with recombinant Mtb9.9A recognized one of the other family members, Mtb9.9C. Synthetic peptides were used to map the T cell epitope recognized by this line, and revealed a single amino acid substitution in this region when compared with Mtb9.9A. The direct identification of antigens using T cells from immune donors will undoubtedly be critical for the development of vaccines to several intracellular pathogens.

Multiepitope synthetic peptide and recombinant protein for the detection of antibodies to Trypanosoma cruzi in patients with treated or untreated Chagas' disease

A tetrapeptide and a recombinant protein, each representing 4 immunodominant epitopes of Trypanosoma cruzi, were tested by use of ELISA for the detection of serum antibodies. Sera from individuals with Chagas' disease, including persons untreated and successfully or unsuccessfully treated, were tested. These assays detected antibody in 100% of the parasitemias. The antibody reactivity decreased based on the success of treatment. Higher sensitivity was observed for tetrapeptide/recombinant protein assays than for lysate-based ELISA, and specificity was improved, particularly with Leishmania sera. The results indicate that multiepitope antigens provide a more sensitive and specific alternative to lysate for detection of anti-T. cruzi antibodies, as required for developing blood screening assays.

Cloning, characterization and serological evaluation of K9 and K26: two related hydrophilic antigens of Leishmania chagasi

We report here the molecular cloning and characterization of two related hydrophilic antigens of Leishmania chagasi. These two antigens have predicted molecular weights of approximately 9 and 26 kDa and detect antibodies in sera of patients with kala-azar (k). Thus, to maintain consistency with nomenclature of the previously described 39 kDa diagnostic antigen of L. chagasi (k39 [1]), these antigens are being referred to as k9 and k26. A significant difference between k9 and k26 is the presence of 11 copies of a 14 amino acid repeat in the open reading frame of k26. The region flanking the repeats of k26 shares a 69% identity with the open reading frame of k9. The recombinant proteins encoded by both antigens are very hydrophilic and show aberrant migration on SDS PAGE. Results of Southern blot analysis reveal that k9 and k26 are conserved to varying degrees among various Leishmania species. Interestingly, the repeat region of k26 is specific to L. chagasi and L. donovani while the flanking region is conserved among several other species. Transcript levels of k26 are significantly upregulated in the amastigote stage of the parasite. Our results show that recombinant K26 is specific in detecting antibodies in infection sera from visceral leishmaniasis (VL) patients. Thus rK26 may complement rK39 in a more accurate diagnosis of VL in the old and the new world.

Cloning, expression, and immunological evaluation of two putative secreted serine protease antigens of Mycobacterium tuberculosis

Culture filtrate proteins (CFP) of Mycobacterium tuberculosis have been shown to contain immunogenic components that elicit at least partial protective immunity against Mycobacterium infection. To clone genes encoding some of the immunogenic proteins, we made a high-titer rabbit anti-CFP serum and used it to screen an M. tuberculosis genomic expression library in Escherichia coli. In this paper, we describe the molecular cloning of two new protein components of CFP and identified them as members of the serine protease gene family. Their open reading frames contain N-terminal hydrophobic secretory signals consistent with their detection in CFP. The predicted molecular masses of the mature, fully processed forms of both antigens are approximately 32 kDa, in agreement with their observed sizes on immunoblots of CFP probed with polyclonal rabbit antisera made to the recombinant proteins. Thus, these proteins have been designated MTB32A and MTB32B. Interestingly, and despite 66% amino acid sequence homology between the two proteins, polyclonal rabbit antisera made to each of the recombinant proteins were found to be specific for the respective immunizing antigens. The recombinant proteins were also evaluated in in vitro assays with donor peripheral blood mononuclear cells (PBMC) from healthy purified protein derivative (PPD)-positive individuals of diverse ethnic backgrounds. MTB32A but not MTB32B stimulated PBMC from healthy PPD-positive donors but not from PPD-negative donors to proliferate and secrete gamma interferon. MTB32A is encoded by a single-copy gene which is present in both virulent and avirulent strains of the M. tuberculosis complex and the BCG strain of Mycobacterium bovis but absent in the environmental mycobacterial species tested. In addition, nucleotide sequence comparison of mtb32a of the avirulent H37Ra strain and the virulent Erdman strain, as well as with the corresponding sequences (identified in the databases) of strain H37Rv and the clinical isolate CSU93, revealed 100% identity. MTB32A, therefore, represents a candidate for inclusion in subunit vaccine development. Finally, the possible role of MTB32 serine proteases as a virulence factor(s) during Mycobacterium spp. infection is discussed.

Molecular characterization and human T-cell responses to a member of a novel Mycobacterium tuberculosis mtb39 gene family

We have used expression screening of a genomic Mycobacterium tuberculosis library with tuberculosis (TB) patient sera to identify novel genes that may be used diagnostically or in the development of a TB vaccine. Using this strategy, we have cloned a novel gene, termed mtb39a, that encodes a 39-kDa protein. Molecular characterization revealed that mtb39a is a member of a family of three highly related genes that are conserved among strains of M. tuberculosis and Mycobacterium bovis BCG but not in other mycobacterial species tested. Immunoblot analysis demonstrated the presence of Mtb39A in M. tuberculosis lysate but not in culture filtrate proteins (CFP), indicating that it is not a secreted antigen. This conclusion is strengthened by the observation that a human T-cell clone specific for purified recombinant Mtb39A protein recognized autologous dendritic cells infected with TB or pulsed with purified protein derivative (PPD) but did not respond to M. tuberculosis CFP. Purified recombinant Mtb39A elicited strong T-cell proliferative and gamma interferon responses in peripheral blood mononuclear cells from 9 of 12 PPD-positive individuals tested, and overlapping peptides were used to identify a minimum of 10 distinct T-cell epitopes. Additionally, mice immunized with mtb39a DNA have shown increased protection from M. tuberculosis challenge, as indicated by a reduction of bacterial load. The human T-cell responses and initial animal studies provide support for further evaluation of this antigen as a possible component of a subunit vaccine for M.tuberculosis.

A multi-epitope synthetic peptide and recombinant protein for the detection of antibodies to Trypanosoma cruzi in radioimmunoprecipitation-confirmed and consensus-positive sera

Peptide epitopes of Trypanosoma cruzi have been identified through expression cloning. A tripeptide (2/D/E) containing three epitopes (TcD, TcE, PEP-2) was used in ELISA to detect antibodies to T. cruzi in 239 of 240 consensus-positive sera and 41 of 42 sera confirmed positive by radioimmunoprecipitation assay. The 1 discrepant consensus-positive serum was used to expression-clone a novel gene that contained a repeat sequence. A peptide corresponding to this sequence, TcLo1.2, was specific for T. cruzi. This antigen detected the discrepant consensus-positive serum and enhanced reactivity of low-positive sera in the tripeptide assay. A branched synthetic peptide, 2/D/E/Lo1.2, or a linear recombinant, r2/D/E/Lo1.2, realized all of the diagnostic features of the four epitopes, including the ability to boost reactivity of low-reactive sera. These studies show that peptides and recombinants containing multiple repeat epitopes are powerful tools for developing assays for T. cruzi antibody detection and have direct application in blood screening.

LeIF: a recombinant Leishmania protein that induces an IL-12-mediated Th1 cytokine profile

We have evaluated the ability of the Leishmania protein LeIF to influence the Th1/Th2 cytokine responses and the generation of LeIF-specific T cell clones in the absence of adjuvant. We characterized LeIF-specific T cell responses in Leishmania major-infected and uninfected BALB/c mice. These mice develop a strong Th2 response during infection with L. major. When lymph node cells from infected BALB/c mice were stimulated in vitro with LeIF, only IFN-gamma (and no detectable IL-4) was found in the culture supernatant. In addition, LeIF down-regulated Leishmania Ag-specific IL-4 production by lymph node cells from infected BALB/c mice. Subsequently, Th responses were evaluated in naive BALB/c mice following immunization with LeIF. T cell clones derived from mice immunized with LeIF preferentially secreted IFN-gamma. Finally, to understand the basis for the preferential Th1 cytokine bias observed with LeIF, the ability of LeIF to influence the early cytokine profile was evaluated in splenocytes of SCID mice. We found that LeIF stimulated fresh spleen cells from naive SCID mice to secrete IFN-gamma by IL-12/IL-18-dependent mechanisms. The N-terminal half of the molecule (amino acid residues 1-226) maintained the ability to stimulate IFN-gamma from splenocytes of SCID mice. Finally, we also demonstrated that LeIF was able to provide partial protection of BALB/c mice against L. major. Thus, our results suggest the potential of LeIF as a Th1-type adjuvant and as a therapeutic and prophylactic vaccine Ag for leishmaniasis when used with other leishmanial Ags.

Molecular cloning and immunologic reactivity of a novel low molecular mass antigen of Mycobacterium tuberculosis

Polypeptide Ags present in the culture filtrate of Mycobacterium tuberculosis were purified and evaluated for their ability to stimulate PBMC from purified protein derivative (PPD)-positive healthy donors. One such Ag, which elicited strong proliferation and IFN-gamma production, was further characterized. The N-terminal amino acid sequence of this polypeptide was determined and used to design oligonucleotides for screening a recombinant M. tuberculosis genomic DNA library. The gene (Mtb 8.4) corresponding to the identified polypeptide was cloned, sequenced, and expressed in Escherichia coli. The predicted m.w. of the recombinant protein without its signal peptide was 8.4 kDa. By Southern analysis, the DNA encoding this mycobacterial protein was found in the M. tuberculosis substrains H37Rv, H37Ra, Erdman, and "C" strain, as well as in certain other mycobacterial species, including Mycobacterium avium and Mycobacterium bovis BCG (bacillus Calmette-Guerin, Pasteur). The Mtb 8.4 gene appears to be absent from the environmental mycobacterial species examined thus far, including Mycobacterium smegmatis, Mycobacterium gordonae, Mycobacterium chelonae, Mycobacterium fortuitum, and Mycobacterium scrofulaceum. Recombinant Mtb 8.4 Ag induced significant proliferation as well as production of IFN-gamma, IL-10, and TNF-alpha, but not IL-5, from human PBMC isolated from PPD-positive healthy donors. Mtb 8.4 did not stimulate PBMC from PPD-negative donors. Furthermore, immunogenicity studies in mice indicate that Mtb 8.4 elicits a Th1 cytokine profile, which is considered important for protective immunity to tuberculosis. Collectively, these results demonstrate that Mtb 8.4 is an immunodominant T cell Ag of M. tuberculosis.

Molecular cloning, expression, and immunogenicity of MTB12, a novel low-molecular-weight antigen secreted by Mycobacterium tuberculosis

Proteins secreted into the culture medium by Mycobacterium tuberculosis are thought to play an important role in the development of protective immune responses. In this report, we describe the molecular cloning of a novel, low-molecular-weight antigen (MTB12) secreted by M. tuberculosis. Sequence analysis of the MTB12 gene indicates that the protein is initially synthesized as a 16.6-kDa precursor protein containing a 48-amino-acid hydrophobic leader sequence. The mature, fully processed form of MTB12 protein found in culture filtrates has a molecular mass of 12. 5 kDa. MTB12 protein constitutes a major component of the M. tuberculosis culture supernatant and appears to be at least as abundant as several other well-characterized culture filtrate proteins, including members of the 85B complex. MTB12 is encoded by a single-copy gene which is present in both virulent and avirulent strains of the M. tuberculosis complex, the BCG strain of M. bovis, and M. leprae. Recombinant MTB12 containing an N-terminal six-histidine tag was expressed in Escherichia coli and purified by affinity chromatography. Recombinant MTB12 protein elicited in vitro proliferative responses from the peripheral blood mononuclear cells of a number of purified protein derivative-positive (PPD+) human donors but not from PPD- donors.

A cloned antigen (recombinant K39) of Leishmania chagasi diagnostic for visceral leishmaniasis in human immunodeficiency virus type 1 patients and a prognostic indicator for monitoring patients undergoing drug therapy

Serologic assays using crude antigens for the diagnosis of visceral leishmaniasis in human immunodeficiency virus type 1 (HIV)-seropositive patients have been shown to lack sensitivity and specificity, particularly in AIDS patients. Antibodies to a cloned antigen, recombinant (r) K39, of Leishmania chagasi are specific for members of the Leishmania donovani complex and have been shown to indicate active disease in immunocompetent persons. This study demonstrated that antibodies to rK39 were also detectable in HIV-seropositive patients coinfected with Leishmania infantum. Furthermore, the rK39 ELISA was more sensitive than an IFA for detecting L. infantum infections in patients with AIDS. In addition, antibody titers to rK39 in HIV-negative patients infected with L. infantum or L. chagasi declined during treatment with meglumine antimoniate or liposomal amphotericin B. In contrast, most patients who clinically relapsed showed increased antibody titers to rK39. These data demonstrate the diagnostic and prognostic utility of rK39 in detecting active visceral leishmaniasis.

Association of Leishmania heat shock protein 83 antigen and immunoglobulin G4 antibody titers in Brazilian patients with diffuse cutaneous leishmaniasis

Diffuse cutaneous leishmaniasis (DCL) is characterized by the presence of numerous nonulcerated nodules and plaques containing large numbers of Leishmania amazonensis parasites and few lymphoid elements. The immune responses of DCL patients reflect severe antigen-specific T-cell deficiencies, while the antibody response to Leishmania antigens is often accentuated. We report herein on the Leishmania antigen-specific antibody subclass distribution in DCL patients and demonstrate that a dominant antigen contributing to the biased immunoglobulin G4 antibody subclass in sera of DCL patients is Leishmania heat shock protein 83.

Molecular characterization of the heat-inducible LmSTI1 protein of Leishmania major

We have recently isolated a cDNA encoding the Leishmania major homologue of the yeast stress-inducible protein STI1. Southern blot analyses indicate that this protein is encoded by a single copy gene in L. major and that this gene is highly conserved throughout the Leishmania genus. The STI1 gene is constitutively expressed in both L. major promastigotes and amastigotes however, STI1 transcript levels can be upregulated in promastigotes by a shift in culture temperature from 26 to 37 degrees C. Upregulation of transcript was detectable within 5' of heat shock and continued to increase for a further 8 h before returning to constitutive levels. In addition, biosynthetic incorporation of [35S]methionine followed by immunoprecipitation revealed an increase in the level of nascent STI1 protein synthesized when promastigote cultures were shifted from 26 to 37 degrees C. The L. major STI1 protein and the heat shock proteins Hsp83 and Hsp70 form a salt-sensitive complex in L. major promastigotes as evidenced by co-immunoprecipitation using an antiserum specific for L. major STI1. Furthermore, this complex can be reconstituted in vitro by adding recombinant STI1 containing an amino-terminal histidine tag to promastigote lysate and subsequent purification using metal chelate affinity chromatography.

A Leishmania protein that modulates interleukin (IL)-12, IL-10 and tumor necrosis factor-alpha production and expression of B7-1 in human monocyte-derived antigen-presenting cells

LeIF, a gene homologue of the eukaryotic initiation factor 4A was first described as a leishmanial antigen that induced a Th1-type T cell response in peripheral blood mononuclear cells (PBMC) from leishmaniasis patients. Moreover, the interferon (IFN)-gamma production by PBMC was found to be interleukin (IL)-12 dependent. Herein, we characterize the effects of LeIF on cytokine production and expression of surface molecules by normal human monocytes as well as by monocyte-derived macrophages and dendritic cells (MoDC). LeIF was a strong inducer of IL-12 and, to a lesser extent, of IL-10 and tumor necrosis factor (TNF)-alpha in macrophages and MoDC. IL-12 production did not require CD40 triggering, confirming that the ability of LeIF to induce IL-12 was not mediated through an effect on T cells. However, addition of soluble CD40 ligand (L) synergistically augmented IL-12 production in macrophages and MoDC. The cytokine-inducing activity of LeIF is located in the N-terminal portion of the molecule and was both proteinase K sensitive and polymyxin B resistant. LeIF, lipopolysaccharide and fixed Staphylococcus aureus all induced comparable amounts of IL-12, validating the potent cytokine-inducing effects of LeIF. Moreover, of these stimuli, LeIF had the highest IL-12/IL-10 and IL-12/TNF-alpha ratio demonstrating the preference of LeIF for IL-12 induction. Studies investigating the expression of surface molecules showed that LeIF up-regulated B7-1 and CD54 (ICAM-1) on macrophages and MoDC. To our knowledge this is the first report describing IL-12 production, up-regulation of co-stimulatory and intercellular adhesion molecules by monocytic antigen-presenting cells in response to a protein from a pathogenic microorganism. These immunomodulatory characteristics of LeIF might be excellent properties for a Th1-type adjuvant.

Molecular cloning and characterization of two iron superoxide dismutase cDNAs from Trypanosoma cruzi

Two cDNAs (FeSODA and FeSODB cDNAs) corresponding to superoxide dismutase (1.15.1.1., SOD) were isolated from a Trypanosoma cruzi cDNA library. Comparison of the deduced amino acid sequences with previously reported SOD protein sequences revealed that the T. cruzi open reading frames had considerable homology with FeSODs. The coding region of the T. cruzi FeSODB cDNA has been expressed in fusion with glutathione-S-transferase using an Escherichia coli mutant QC779, lacking both MnSOD and FeSOD genes (sodA sodB). Staining of native polyacrylamide gels for SOD activity of T cruzi crude lysate and the recombinant SOD suggests that this protein is an FeSOD. The recombinant enzyme also protected the E. coli mutant QC779 from paraquat toxicity. Northern blot analysis showed that FeSODB is differentially expressed, showing a higher level at the epimastigote stage of T. cruzi development; whereas, FeSODA is constitutively expressed at a lower level in all developmental stages. Furthermore, Southern hybridization shows that both FeSODA and FeSODB genes appear to be present in the T. cruzi genome as multiple repeating units (multi-copy gene family).

Cloning and expression of a Leishmania donovani gene instructed by a peptide isolated from major histocompatibility complex class II molecules of infected macrophages

The studies reported here describe the isolation of peptides from MHC class II molecules of murine macrophages infected with Leishmania donovani, and the use of the derived peptide sequences to rescue the pathogen peptide donor protein. The isolation of the peptides was carried out by comparing the RP HPLC profile of peptides extracted from infected macrophages with the peptides extracted from noninfected cells. Several distinct HPLC peaks unique to infected macrophages were sequenced. One of the peptides that was not homologous to any known protein was used to instruct the designing of an oligonucleotide sense primer that was used in combination with an oligo dT nucleotide (anti-sense primer) to amplify by PCR a DNA fragment from L. donovani cDNA. The amplified DNA fragment was cloned and used as a probe to screen a L. donovani cDNA library. The cloned gene (Ld peptide gene) has an open reading frame of 525 bp and has no homology with any known protein/gene sequence. Northern blot analyses indicated that the Ld peptide/gene is broadly distributed and expressed among species of the Leishmania genus, in both the amastigote and promastigote life cycle forms. Using the pGEX 2T vector, the gene was expressed and the relationship of the purified recombinant protein with L. donovani was confirmed using both antibody and T cell responses from immunized or infected animals. The gene encodes a 23-kD molecule (Ldp 23) associated with the cell surface of L. donovani promastigotes. In addition, T cells purified from the lymph nodes of BALB/c mice immunized with L. donovani or infected with L. major, and from CBA/J mice infected with L. amazonensis were stimulated to proliferate by the recombinant Ldp 23 and produced high levels of IFN-gamma and no IL 4. This observation suggests that the Ldp 23 is an interesting parasite molecule for the studies concerning the host/parasite interaction because the Th1 pattern of cytokine response that it induces is correlated with resistance to Leishmania infections. These results clearly point to an alternative strategy for the purification of proteins useful for the development of both vaccines and immunological diagnostic tools not only against leishmaniasis but also for other diseases caused by intracellular pathogens.

Immune responses of leishmaniasis patients to heat shock proteins of Leishmania species and humans

The course of human infection with Leishmania braziliensis is variable, ranging from self-healing infection to chronic disease. It is therefore a useful system in which to study immunoregulatory aspects of leishmaniasis, including the effects of parasite antigens on host responses. In the present study, we report on the cloning of, expression of, and comparative analyses of patient immune response to two different L. braziliensis genes homologous to the genes for the eukaryotic 83- and 70-kDa heat shock proteins. rLbhsp83 contains a potent T-cell epitope(s) which stimulated peripheral blood mononuclear cells (PBMC) from all L. braziliensis-infected individuals to proliferate and to produce interleukin-2 (IL-2) gamma interferon, and tumor necrosis factor alpha. The elicitation of IL-4 and IL-10 mRNAs was found to differ depending on the portion of the rLbhsp83 used to stimulate PBMC. rLbhsp83a, which represents the nearly full-length protein, stimulated IL-10 but not IL-4 mRNA. In contrast, a approximately 43-kDa protein representing the C-terminal region of Lbhsp83 stimulated the production of IL-4 but not IL-10 mRNA. rLbhsp70 stimulated PBMC proliferation from patients with mucosal disease but, unlike rLbhsp83, did not stimulate PBMC from self-healing individuals. PBMC from mucosal patients were not stimulated by rHuhsp70 to either proliferate or produce cytokines. This suggests that the hyperresponsiveness of mucosal patient PBMC to Leishmania heat shock proteins does not involve an auto-immune phenomenon resulting from cross-reactivity with self hsp70. In general, although the cytokine profile of patient PBMC in response to both of these Leishmania heat shock proteins represents a mixed Th1-Th2 pattern, the levels of gamma interferon and IL-2 were significantly higher than those of the Th2 cytokines IL-4 and IL-10. Patients with active mucosal and cutaneous disease but not self-healing individuals had significant anti-immunoglobulin G antibody titers to both rLbhsp83 and rLbhsp70 but not to the homologous rHuhsp70. It therefore appears that differential patient immune responses to Leishmania hsp83 and hsp70 may be of particular significance in the induction of protective immune responses as well as in the development of tissue damage in cases with particularly strong hypersensitive reactions.

A recombinant Leishmania antigen that stimulates human peripheral blood mononuclear cells to express a Th1-type cytokine profile and to produce interleukin 12

Leishmania braziliensis causes cutaneous and mucosal leishmaniasis in humans. Most patients with cutaneous leishmaniasis heal spontaneously and may therefore have developed protective immunity. There appears to be a mixed cytokine profile associated with active cutaneous or mucosal disease, and a dominant T helper (Th)1-type response associated with healing. Leishmanial antigens that elicit these potent proliferative and cytokine responses from peripheral blood mononuclear cells (PBMC) are now being identified. Herein, we report on the cloning and expression of a L. braziliensis gene homologous to the eukaryotic ribosomal protein eIF4A (LeIF) and patient PBMC responses to rLeIF. Patients with mucosal and self-healing cutaneous disease had significantly higher proliferative responses than those with cutaneous lesions. Whereas the parasite lysate stimulated patient PBMC to produce a mixed Th1/Th2-type cytokine profile, LeIF stimulated the production of interferon gamma (IFN-gamma), interleukin 2 (IL-2), and tumor necrosis factor alpha but not IL-4 or IL-10. Recombinant LeIF (rLeIF) downregulated both IL-10 mRNA in the "resting" PBMC of leishmaniasis patients and LPS-induced IL-10 production by patient PBMC. rLeIF also stimulated the production of IL-12 in cultured PBMC from both patients and uninfected individuals. The production of IFN-gamma by patient PBMC stimulated with either rLeIF or parasite lysate was IL-12 dependent, whereas anti-IFN-gamma monoclonal antibody only partially blocked the LeIF-induced production of IL-12. In vitro production of both IFN-gamma and IL-12 was abrogated by exogenous human recombinant IL-10. Therefore, we have identified a recombinant leishmanial antigen that elicits IL-12 production and Th1-type responses in patients as well as IL-12 production in normal human PBMC.

Antigens shared by Leishmania species and Trypanosoma cruzi: immunological comparison of the acidic ribosomal P0 proteins

Patients with visceral leishmaniasis produce high levels of immunoglobulin, but the specificities of antibodies produced are not well characterized. In an effort to identify leishmania antigens that are specific to Leishmania species or are cross-reactive with other parasitic protozoa, we have cloned and characterized full-length genomic and cDNA clones encoding a Leishmania chagasi acidic ribosomal antigen, LcP0, recognized during human infections. The protein is homologous to the Trypanosoma cruzi and human ribosomal proteins TcP0 and HuP0, respectively. Unlike most higher eukaryotes, but similar to TcP0, LcP0 has a C-terminal heptapeptide sequence resembling those of the archaebacterial acidic (P-like) proteins. The highly charged C-terminal acidic domain of LcP0 contains a serine residue typically found in most eukaryotes but lacking in all T. cruzi P proteins we have characterized thus far. L. chagasi-infected individuals as well as those with T. cruzi infections have antibodies cross-reactive with recombinant LcP0 and TcP0 as well as HuP0. However, the properties of anti-P0 antibodies in T. cruzi and L. chagasi infection sera are quite different. Through the use of synthetic peptides, we showed that while T. cruzi infection anti-TcP0 antibodies are exclusively directed against the C-terminal domain of TcP0, L. chagasi infection sera contain antibodies reactive with epitopes other than the C-terminal sequence of LcP0. Thus, anti-LcP0 antibodies in L. chagasi infection sera represent the first characterized deviation from the restricted immunodominant C-terminal epitope involved in the generation of anti-P0 antibodies following infection or autoimmune diseases.

Protein phosphorylation and control of chorion gene activation through temporal mobilization of a promoter DNA binding factor from the cytoplasm into the nucleus

The transcriptional activation of high cysteine chorion genes in the follicular cells of the silkworm Bombyx mori occurs at the end of oogenesis and coincides with the appearance of a chorion promoter DNA binding factor, BCFI, in follicular cell nuclei. Follicular cells of vitellogenic and choriogenic follicles that do not express high cysteine chorion genes contain high levels of a latent form of BCFI in their cytoplasm. The abundance of the cytoplasmic factor, termed cBCFI, is dramatically reduced during late choriogenesis, coincident with the appearance of factor BCFI in the nucleus and the transcriptional activation of high cysteine genes. Mobility shift assays performed with partially proteolyzed nuclear and cytoplasmic extracts of follicular cells, DNA binding assays carried out in the presence of anti-BCFI antibodies, and electrophoretic analyses of the proteins present in the nuclear and cytoplasmic fractions of follicular cells and recognized by the same antibodies suggest that factor cBCFI represents a covalently modified version of BCFI. The DNA-binding sites of BCFI and cBCFI include a core sequence, AGATAA, but, while this sequence is sufficient for specific binding of BCFI, it only constitutes part of the DNA-binding site of cBCFI. Dephosphorylation of cBCFI results in a change of its binding specificity to that of BCFI. The cytoplasmic sequestration of cBCFI appears to be mediated by a phosphorylation-dependent, reversible association of this factor with an ancillary cytoplasmic factor.

GATA-type zinc finger motif-containing sequences and chorion gene transcription factors of the silkworm Bombyx mori

To characterize a DNA-binding protein, BCFI, which regulates the expression of silkmoth chorion genes through binding to gene promoter elements identical to those recognized by the GATA family of transcription factors, we have carried out polymerase chain reaction amplifications of Bombyx mori genomic DNA using degenerate primers derived from the conserved DNA binding domain of mammalian GATA factors. Two single copy genes, BmGATA alpha and BmGATA beta, were identified, which encode sequences containing GATA-type zinc finger motifs. The BmGATA beta gene is expressed in follicular and Bm5 tissue culture cells, the two cell types that contain BCFI. No BmGATA alpha gene transcripts were detectable in the tissues that were tested. Upon overexpression in Escherichia coli, a peptide encompassing the BmGATA beta zinc finger motif was able to bind specifically to the BCFI recognition motif of the chorion gene promoters. A polyclonal antibody directed against the zinc finger domain of BmGATA beta was also used in gel retardation assays to confirm that factor BCFI is indeed encoded by the BmGATA beta gene. Conceptual translation of a complete cDNA clone encoding the BmGATA beta protein revealed that this protein has a size similar to that of an immunoreactive protein, presumably BCFI, which is present in follicular cell extracts.

Molecular cloning, characterization, and expression in Escherichia coli of iron superoxide dismutase cDNA from Leishmania donovani chagasi

A cDNA corresponding to superoxide dismutase (SOD; EC 1.15.1.1.) was isolated from a Leishmania donovani chagasi (L. d. chagasi) promastigote cDNA library, using PCR with a set of primers derived from conserved amino acids of manganese SODs (MnSODs) and iron SODs (FeSODs). Comparison of the deduced amino acid sequences with previously reported SOD amino acid sequences revealed that the L. d. chagasi 585-bp open reading frame had considerable homology with FeSODs and MnSODs. The highest homology was shared with prokaryotic FeSODs. The coding region of L. d. chagasi SOD cDNA has been expressed in fusion with glutathione-S-transferase, using an Escherichia coli mutant, QC779, lacking both MnSOD and FeSOD genes (sodA and sodB). Staining of native polyacrylamide gels for SOD activity of Leishmania crude lysate and the recombinant SOD revealed that both had SOD activity that was inactivated by 5 mM hydrogen peroxide but not by 2 mM potassium cyanide, which is indicative of FeSOD. The recombinant enzyme also protected E. coli mutant QC779 from paraquat toxicity. This indicated that the glutathione-S-transferase peptide does not interfere with the in vivo and in vitro activities of the recombinant SOD. Cross-species hybridization showed that FeSOD is highly conserved in the Leishmania genus. Interestingly, the hybridization pattern of the FeSOD gene(s) coincided with other classification schemes that divide Leishmania species into complexes. The cloning of FeSOD cDNA may contribute to the understanding of the role of SODs in Leishmania pathogenesis.

Trypanosoma cruzi acidic ribosomal P protein gene family. Novel P proteins encoding unusual cross-reactive epitopes

We have cloned and characterized cDNA molecules that encode members of the acidic ribosomal protein family (TcP proteins) from the protozoan parasite Trypanosoma cruzi. These proteins have been shown to be antigenic in individuals with T. cruzi infection. Unlike other known eukaryotic cells, T. cruzi possesses at least four types of P protein genes TcP0, TcP1, TcP2a, and TcP2b, each of which is present in multiple copies in the genome. These genes are present on at least three different chromosomes. Although the abundance of TcP0, TcP2a, and TcP2b transcripts do not appear to vary among the parasite life-cycle stages, TcP1 is predominantly expressed in the epimastigote (insect) stage. TcP0 has a C-terminal heptapeptide sequence that is similar to those of archaebacterial acidic (P-like) proteins, but the TcP1/P2 proteins terminate with a shared sequence characteristic of the P proteins of higher eukaryotes. The serine residues or other potential phosphorylation sites typically found within the highly charged C-terminal acidic domain are absent in T. cruzi P proteins. Using synthetic peptides, we demonstrated that approximately 80% of T. cruzi-infected individuals produce two distinct but cross-reactive anti-P antibody specificities directed against the C-termini of TcP0 and TcP1/P2. We also expressed the full length (non-fusion) recombinant human P0 and demonstrated that the T. cruzi anti-P antibodies cross-react with the C-terminal residues of human P-proteins. Conversely, human anti-P protein antibodies in sera from patients with SLE cross-react with the C-terminal epitope of T. cruzi TcP1/P2 proteins. The cross-reactivity of anti-TcP antibodies with human P proteins suggests that, through antigenic conservation, TcP proteins may contribute to the development of autoreactive antibodies in Chagas' disease patients.

Trypanosoma cruzi acidic ribosomal P protein gene family. Novel P proteins encoding unusual cross-reactive epitopes

We have cloned and characterized cDNA molecules that encode members of the acidic ribosomal protein family (TcP proteins) from the protozoan parasite Trypanosoma cruzi. These proteins have been shown to be antigenic in individuals with T. cruzi infection. Unlike other known eukaryotic cells, T. cruzi possesses at least four types of P protein genes TcP0, TcP1, TcP2a, and TcP2b, each of which is present in multiple copies in the genome. These genes are present on at least three different chromosomes. Although the abundance of TcP0, TcP2a, and TcP2b transcripts do not appear to vary among the parasite life-cycle stages, TcP1 is predominantly expressed in the epimastigote (insect) stage. TcP0 has a C-terminal heptapeptide sequence that is similar to those of archaebacterial acidic (P-like) proteins, but the TcP1/P2 proteins terminate with a shared sequence characteristic of the P proteins of higher eukaryotes. The serine residues or other potential phosphorylation sites typically found within the highly charged C-terminal acidic domain are absent in T. cruzi P proteins. Using synthetic peptides, we demonstrated that approximately 80% of T. cruzi-infected individuals produce two distinct but cross-reactive anti-P antibody specificities directed against the C-termini of TcP0 and TcP1/P2. We also expressed the full length (non-fusion) recombinant human P0 and demonstrated that the T. cruzi anti-P antibodies cross-react with the C-terminal residues of human P-proteins. Conversely, human anti-P protein antibodies in sera from patients with SLE cross-react with the C-terminal epitope of T. cruzi TcP1/P2 proteins. The cross-reactivity of anti-TcP antibodies with human P proteins suggests that, through antigenic conservation, TcP proteins may contribute to the development of autoreactive antibodies in Chagas' disease patients.

Interleukin 10 production correlates with pathology in human Leishmania donovani infections

We have found that an important Th2 cytokine, IL-10, is produced by tissues from patients acutely infected with Leishmania donovani. In all individuals tested, IL-10 mRNA production was increased in lymph nodes taken during acute disease over that observed in postacute samples. In contrast, both pre- and posttreatment lymph nodes had readily detected mRNA for IFN-gamma and IL-2. A down-regulating effect of IL-10 on leishmania-induced proliferative responses was demonstrated when Hu rIL-10 was added to cultures of PBMC from clinically cured individuals. PBMC from individuals with acute visceral leishmaniasis responded to stimulation with leishmania lysate by producing IL-10 mRNA. Simultaneously cultured PBMC collected from the same patients after successful chemotherapy produced no detectable IL-10 mRNA after leishmania antigen stimulation. Neutralizing anti-IL-10 mAb added to PBMC from patients with acute visceral leishmaniasis markedly increased the proliferative response to leishmania lysate. Finally, we observed mRNA for IL-10 and IFN-gamma concurrently in a lesion from a patient with post-kala-azar dermal leishmaniasis (PKDL). These results indicate the production of IL-10 during L. donovani infection, and suggest a role for this cytokine in the regulation of immune responsiveness during visceral leishmaniasis.

Characterization of responses of normal human T cells to Trypanosoma cruzi antigens

The stimulation of normal human PBMC by Trypanosoma cruzi Ag was analyzed. PBMC showed significant in vitro proliferation in response to parasite lysate (Tct), with stimulation indices ranging from 10 to 400, peaking at 6 to 7 days. The cells stimulated with Tct produced significant levels of IL-2. To determine which cells proliferated in response to Tct, PBMC were separated into T- and B-enriched cell populations. Purified T cells, but not B cells, proliferated strongly to Tct. The T cell response required APC and was processing dependent. T cell lines generated against Tct proliferated in response to parasite lysate only in the presence of autologous APC and produced IL-2, IL-6, and IFN-gamma but not IL-4 in response to PMA plus ionomycin. Although there were a significant number of CD45Ra+ cells, the majority of the cells in these T cell lines were CD45Ro+. The V beta usage of Tct-responding T cells was heterogeneous, with most V beta genes represented among the responding cells. An immunodominant repeat Ag (TcD) and a ribosomal phosphoprotein (P0) of T. cruzi elicited strong proliferative responses in all subjects tested. These data indicate the presence of T cell-stimulatory Ag in Tct, characterized by nonpreferential usage of the V beta gene families. The strong stimulation of normal human PBMC by Tct may contribute to immunologic alterations seen in T. cruzi infection.

Characterization of responses of normal human T cells to Trypanosoma cruzi antigens

The stimulation of normal human PBMC by Trypanosoma cruzi Ag was analyzed. PBMC showed significant in vitro proliferation in response to parasite lysate (Tct), with stimulation indices ranging from 10 to 400, peaking at 6 to 7 days. The cells stimulated with Tct produced significant levels of IL-2. To determine which cells proliferated in response to Tct, PBMC were separated into T- and B-enriched cell populations. Purified T cells, but not B cells, proliferated strongly to Tct. The T cell response required APC and was processing dependent. T cell lines generated against Tct proliferated in response to parasite lysate only in the presence of autologous APC and produced IL-2, IL-6, and IFN-gamma but not IL-4 in response to PMA plus ionomycin. Although there were a significant number of CD45Ra+ cells, the majority of the cells in these T cell lines were CD45Ro+. The V beta usage of Tct-responding T cells was heterogeneous, with most V beta genes represented among the responding cells. An immunodominant repeat Ag (TcD) and a ribosomal phosphoprotein (P0) of T. cruzi elicited strong proliferative responses in all subjects tested. These data indicate the presence of T cell-stimulatory Ag in Tct, characterized by nonpreferential usage of the V beta gene families. The strong stimulation of normal human PBMC by Tct may contribute to immunologic alterations seen in T. cruzi infection.

Transforming growth factor-beta in leishmanial infection: a parasite escape mechanism

The course of infection with the protozoan parasite Leishmania is determined in part by their early replication in macrophages, the exclusive host cells for these organisms. Although factors contributing to the survival of Leishmania are not well understood, cytokines influence the course of infection. Transforming growth factor-beta (TGF-beta) is a multipotential cytokine with diverse effects on cells of the immune system, including down-regulation of certain macrophage functions. Leishmanial infection induced the production of active TGF-beta, both in vitro and in vivo. TGF-beta was important for determining in vivo susceptibility to experimental leishmanial infection.

Cloning and expression of Trypanosoma cruzi ribosomal protein P0 and epitope analysis of anti-P0 autoantibodies in Chagas' disease patients

Chagas' disease, caused by the intracellular protozoan parasite Trypanosoma cruzi, is a major cause of heart failure in endemic areas. Antigenic mimicry by T. cruzi antigens sharing epitopes with host macromolecules has been implicated in the pathogenesis which is thought to have a significant autoimmune component. We report herein on the cloning and characterization of a full-length cDNA from a T. cruzi expression library encoding a protein, TcP0, that is homologous to the human 38-kD ribosomal phosphoprotein HuP0. The T. cruzi P0 protein shows a clustering of residues that are evolutionarily conserved in higher eukaryotes. This includes an alanine- and glycine-rich region adjacent to a highly charged COOH terminus. This "hallmark" domain is the basis of the crossreactivity of the highly immunogenic eukaryotic P protein family. We found that T. cruzi-infected individuals have antibodies reacting with host (self) P proteins, as well as with recombinant TcP0. Deletion of the six carboxy-terminal amino acids abolished the reactivity of the T. cruzi infection sera with TcP0. This is similar to the specificity of anti-P autoantibodies described for a subset of patients with systemic lupus erythematosus (SLE) (Elkon, K., E. Bonfa, R. Llovet, W. Danho, H. Weissbach, and N. Brot. 1988. Proc. Natl. Acad. Sci. USA. 85:5186). These results suggest that T. cruzi P proteins may contribute to the development of autoreactive antibodies in Chagas' disease, and that the underlying mechanisms of anti-P autoantibody may be similar in Chagas' and SLE patients. This study represents the first definitive report of the cloning of a full-length T. cruzi antigen that mimics a characterized host homologue in structure, function, and shared antigenicity.

Developmental regulation of covalent modification of double-stranded RNA during silkmoth oogenesis

Follicular cells of the silkmoth Bombyx mori contain an enzymatic activity that modifies RNA duplexes in vitro. The modifying activity converts adenosine residues into inosine in duplex but not single-stranded RNA and mediates the partial unwinding of the complement strands. Because of the modification, the RNA loses its ability to form perfect duplexes with its complement upon reannealing in vitro. The modifying enzyme is localized in the cytoplasm of follicular cells and its activity is modulated in a developmentally regulated manner. In contrast, follicular nuclei contain an activity that inhibits the modification and unwinding of duplex RNA. The modifying activity is also present in the cytoplasm of unfertilized oocytes and its accumulation during oogenesis parallels that of the follicular cells. Examination of an established silkmoth cell line of ovarian origin revealed that, in contrast to the situation with follicular cells, the modifying activity has an exclusive nuclear localization. The cytoplasmic fraction of these cells is not only devoid of modifying activity but, as is the case with the nuclear fraction of follicular cells, contains an activity that inhibits duplex RNA modification and unwinding. We conclude that the modification promoting and inhibiting activities are not restricted to a single cell type and that their compartmentalization is developmentally regulated.

Synergistic interactions of silkmoth chorion promoter-binding factors

Two DNA-binding proteins, BCFI and BCFII, that interact with defined promoter sequences of silkmoth chorion genes of late developmental specificity appear in the nuclei of follicular cells at a time that coincides with the transcriptional activation of the corresponding genes. BCFI prebinding is shown to be indispensable for stable binding of BCFII to its cognate sequence. BCFI and BCFII synergism requires a relatively stringent stereospecific alignment and is a prerequisite for the assembly of higher-order protein-promoter DNA complexes containing additional factors, which are neither gene (stage) nor class (chorion) specific. Binding of BCFI to its site correlates with the induction of DNA structural perturbations that may facilitate assembly of additional factors on the promoter. The BCFI-binding domain contains a core hexanucleotide sequence, AGATAA, which represents the major binding determinant of the erythroid-specific transcription factor GATA-1 of higher vertebrates. This sequence is shown to be necessary and sufficient for binding of BCFI, as it is for a factor that is present in induced K562 human erythroleukemic cells, presumably GATA-1. Comparative analyses of mobility shift patterns obtained with partially proteolyzed preparations of these two unrelated factors were used to confirm that a BCFI-like chorion promoter-binding protein, which is present in the nuclei of an established silkmoth cell line derived from ovarian tissue, is in fact BCFI. The transcriptional repression of endogenous chorion genes in this cell line coupled with the documented absence of factor BCFII suggests that the synergistic interactions between these two factors constitute a minimum requirement for late chorion gene expression.

Silkmoth chorion antisense RNA. Structural characterization, developmental regulation and evolutionary conservation

Choriogenic follicular cells of the silkmoth Bombyx mori contain significant quantities of antisense RNA transcribed from chorion genes. Antisense RNA derived from a chorion gene with a high content of cysteine, HcB.12, was characterized in detail. The antisense transcripts are initiated downstream from the 3' end of HcB.12 mRNA and extend over 75% of the length of the gene, comprising its entire second exon and part of its intervening sequence. The antisense RNA is devoid of any significant open reading frames and is not polyadenylated. These features, combined with the presence of specific sequence motifs within its transcribed and upstream region, suggest that antisense RNA may be transcribed by RNA polymerase III. Chorion antisense RNA is detectable only in choriogenic follicular cells and appears to be co-ordinately regulated with chorion mRNA. Its cytoplasmic accumulation during choriogenesis parallels that of the corresponding mRNA. Although chorion mRNA is at least five times more abundant than antisense RNA, the latter is present as a single-stranded entity in follicular cytoplasm but can form perfect duplexes with its mRNA complement upon annealing in vitro. The possible involvement of antisense RNA transcription in the pathway that controls the programmed expression of chorion genes at the level of transcription initiation or post-transcriptional processing is discussed.

Transcriptional behavior of silkmoth chorion genes in vivo and in injected Xenopus laevis oocytes

A cloned fragment of Bombyx mori genomic DNA containing a pair of chorion genes was injected into Xenopus laevis oocytes. The RNA transcribed from the injected template was examined by primer extension analysis for the presence of transcripts initiated correctly from the two chorion genes. Using as primers a number of fragments derived from various parts of the injected DNA, we have found that transcription initiation around the cap sites of the chorion genes was considerably more frequent than that at other, seemingly random sites of the template. Injection of different quantities of template into the oocytes revealed that at high DNA concentrations, most transcripts were randomly initiated. However, when reduced amounts of DNA were injected into the oocytes, the extent of specific transcription increased dramatically while the proportion of nonspecific transcripts correspondingly decreased. The relative rates of specific initiation from the two chorion genes in injected oocytes resembled closely those observed in choriogenic follicles. Finally, the primer extension analysis revealed the presence of chorion antisense transcripts not only in injected oocytes but also in total RNA derived from follicular cells. The possible origin of these transcripts is discussed.