Structural and functional properties of complement-activating protein M161Ag, a Mycoplasma fermentans gene product that induces cytokine production by human monocytes

Role of Mycoplasma Chaperone DnaK in Cellular Transformation

Studies of the human microbiome have elucidated an array of complex interactions between prokaryotes and their hosts. However, precise bacterial pathogen-cancer relationships remain largely elusive, although several bacteria, particularly those establishing persistent intra-cellular infections, like mycoplasmas, can alter host cell cycles, affect apoptotic pathways, and stimulate the production of inflammatory substances linked to DNA damage, thus potentially promoting abnormal cell growth and transformation. Consistent with this idea, in vivo experiments in several chemically induced or genetically deficient mouse models showed that germ-free conditions reduce colonic tumor formation. We demonstrate that mycoplasma DnaK, a chaperone protein belonging to the Heath shock protein (Hsp)-70 family, binds Poly-(ADP-ribose) Polymerase (PARP)-1, a protein that plays a critical role in the pathways involved in recognition of DNA damage and repair, and reduces its catalytic activity. It also binds USP10, a key p53 regulator, reducing p53 stability and anti-cancer functions. Finally, we showed that bystander, uninfected cells take up exogenous DnaK-suggesting a possible paracrine function in promoting cellular transformation, over and above direct mycoplasma infection. We propose that mycoplasmas, and perhaps certain other bacteria with closely related DnaK, may have oncogenic activity, mediated through the inhibition of DNA repair and p53 functions, and may be involved in the initiation of some cancers but not necessarily involved nor necessarily even be present in later stages.

Activation of NLRP3 inflammasome in macrophages by mycoplasmal lipoproteins and lipopeptides

The NLRP3 inflammasome, an intracellular sensor consisting of the nucleotide-binding oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3), the adaptor protein apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC), and procaspase-1, plays critical roles in host defense against microbial pathogens by inducing production of interleukin-1β (IL-1β) and IL-18. Mycoplasma salivarium and Mycoplasma pneumoniae cells activated murine bone marrow-derived macrophages (BMMs) to induce production of IL-1α, IL-1β, and IL-18. The IL-1β production-inducing activities of these mycoplasmas toward BMMs from Toll-like receptor 2 (TLR2)-deficient mice were significantly attenuated compared with those from C57BL/6 mice (B6BMMs). This result suggests the possibility that their lipoproteins as TLR2 agonists are involved in the activity. Lipoproteins of M. salivarium and M. pneumoniae (MsLP and MpLP), and the M. salivarium-derived lipopeptide FSL-1 induced IL-1β production by B6BMMs, but not by BMMs from caspase-1-, NLRP3- or ASC-deficient mice. The activities of MsLP and MpLP were not downregulated by the proteinase K treatment, suggesting that the active sites are their N-terminal lipopeptide moieties. B6BMMs internalized the mycoplasmal N-terminal lipopeptide FSL-1 at least 30 min after incubation, FSL-1-containing endosomes started to fuse with the lysosomes around 2 hours, and then FSL-1 translocated into the cytosol from LAMP-1⁺ endosomes. The artificial delivery of FSL-1 into the cytosol of B6BMMs drastically enhanced the IL-1β production-inducing activity. FSL-1 as well as the representative NLRP3 inflammasome activator nigericin induced the NLRP3/ASC speck, but FSL-1 located in a compartment different from the NLRP3/ASC speck.

Development of a vaccine based on bacteria-mimicking tumor cells coated with novel engineered toll-like receptor 2 ligands

For a successful tumor vaccine, it is necessary to develop effective immuno-adjuvants and identify specific tumor antigens. Tumor cells obtained from surgical or biopsy tissues are a good source of tumor antigens but, unlike bacteria, they do not induce strong immune responses. Here, we designed 2 novel lipopeptides that coat tumor cell surfaces and mimic bacterial components. Tumor cells coated with these lipopeptides (called bacteria-mimicking tumor cells [BMTC]) were prepared and their efficacy as a tumor vaccine examined. Natural bacterial lipopeptides act as ligands for toll-like receptor 2 (TLR2) and activate dendritic cells (DC). To increase the affinity of the developed lipopeptides for the negatively charged plasma membrane, a cationic polypeptide was connected to Pam2Cys (P2C), which is the basic structure of the TLR2 ligand. This increased the non-specific binding affinity of the peptides for the cell surface. Two such lipopeptides, P2CSK11 (containing 1 serine and 11 lysine residues) and P2CSR11 (containing 1 serine and 11 arginine residues) bound to irradiated tumor cells via the long cationic polypeptides more efficiently than the natural lipopeptide MALP2 (P2C-GNNDESNISFKEK) or a synthetic lipopeptide P2CSK4 (a short cationic polypeptide containing 1 serine and 4 lysines). BMTC coated with P2CSR11 or P2CSK11 were efficiently phagocytosed by DC and induced antigen cross-presentation in vitro. They also induced effective tumor-specific cytotoxic T cell responses and inhibited tumor growth in in vivo mouse models. P2CSR11 activated DC but induced less inflammation-inducing cytokines/interferons than other lipopeptides. Thus, P2CSR11 is a strong candidate antigen-specific immuno-adjuvant, with few adverse effects.

Type I Interferon-Independent Dendritic Cell Priming and Antitumor T Cell Activation Induced by a Mycoplasma fermentans Lipopeptide

Mycoplasma fermentans-derived diacylated lipoprotein M161Ag (MALP404) is recognized by human/mouse toll-like receptor (TLR) 2/TLR6. Short proteolytic products including macrophage-activating lipopeptide 2 (MALP2) have been utilized as antitumor immune-enhancing adjuvants. We have chemically synthesized a short form of MALP2 named MALP2s (S-[2,3-bis(palmitoyloxy)propyl]-CGNNDE). MALP2 and MALP2s provoke natural killer (NK) cell activation in vitro but only poorly induce tumor regression using in vivo mouse models loading NK-sensitive tumors. Here, we identified the functional mechanism of MALP2s on dendritic cell (DC)-priming and cytotoxic T lymphocyte (CTL)-dependent tumor eradication using CTL-sensitive tumor-implant models EG7 and B16-OVA. Programmed death ligand-1 (PD-L1) blockade therapy in combination with MALP2s + ovalbumin (OVA) showed a significant additive effect on tumor growth suppression. MALP2s increased co-stimulators CD80/86 and CD40, which were totally MyD88-dependent, with no participation of toll-IL-1R homology domain-containing adaptor molecule-1 or type I interferon signaling in DC priming. MALP2s + OVA consequently augmented proliferation of OVA-specific CTLs in the spleen and at tumor sites. Chemokines and cytolytic factors were upregulated in the tumor. Strikingly, longer duration and reinvigoration of CTLs in spleen and tumors were accomplished by the addition of MALP2s + OVA to α-PD-L1 antibody (Ab) therapy compared to α-PD-L1 Ab monotherapy. Then, tumors regressed better in the MALP2s/OVA combination than in the α-PD-L1 Ab monotherapy. Hence, MALP2s/tumor-associated antigens combined with α-PD-L1 Ab is a good therapeutic strategy in some mouse models. Unfortunately, numerous patients are still resistant to PD-1/PD-L1 blockade, and good DC-priming adjuvants are desired. Cytokine toxicity by MALP2s remains to be settled, which should be improved by chemical modification in future studies.

Development of a dendritic cell-targeting lipopeptide as an immunoadjuvant that inhibits tumor growth without inducing local inflammation

Materials used for the past 30 years as immunoadjuvants induce suboptimal antitumor immune responses and often cause undesirable local inflammation. Some bacterial lipopeptides that act as Toll-like receptor (TLR) 2 ligands activate immune cells as immunoadjuvants and induce antitumor effects. Here, we developed a new dendritic cell (DC)-targeting lipopeptide, h11c (P2C-ATPEDNGRSFS), which uses the CD11c-binding sequence of intracellular adhesion molecule-1 to selectively and efficiently activate DCs but not other immune cells. Although the h11c lipopeptide activated DCs similarly to an artificial lipopeptide, P2C-SKKKK (P2CSK4), via TLR2 in vitro, h11c induced more effective tumor inhibition than P2CSK4 at low doses in vivo with tumor antigens. Even without tumor antigens, h11c lipopeptide significantly inhibited tumor growth and induced tumor-specific cytotoxic T cells. P2CSK4 was retained subcutaneously at the vaccination site and induced severe local inflammation in in vivo experiments. In contrast, h11c was not retained at the vaccination site and was transported into the tumor within 24 hr. The recruitment of DCs into the tumor was induced by h11c more effectively, while P2CSK4 induced the accumulation of neutrophils leading to severe inflammation at the vaccination site. Because CD11b+ cells, but not CD11c+ cells, produced neutrophil chemotactic factors such as macrophage inflammatory protein (MIP)-2 in response to stimulation with TLR2 ligands, the DC-targeting lipopeptide h11c induced less MIP-2 production by splenocytes than P2CSK4. In this study, we succeeded in developing a novel immunoadjuvant, h11c, which effectively induces antitumor activity without adverse effects such as local inflammation via the selective activation of DCs.

Effects of Ureaplasma urealyticum lipid-associated membrane proteins on rheumatoid arthritis synovial fibroblasts

Objectives

As an infectious agent might play a role in rheumatoid arthritis (RA) development, this study investigated effects of Ureaplasma urealyticum lipid-associated membrane proteins (UuLAMPs) on RA synovial fibroblast (RASF) proliferation, and tumour necrosis factor (TNF)-α and interleukin (IL)-1β production by THP-1 macrophages. Possible immunogenic proteins in UuLAMPs were identified.

Methods

RASFs were cultured from synovial tissue from donors with RA. Serum samples from donors with/without RA and with/without U. urealyticum infection were used for immunogenicity analyses. THP-1 macrophages served as a model for synovial macrophages. TNF-α and IL-1β mRNA levels were assessed using reverse transcription–polymerase chain reaction; protein levels were estimated using enzyme-linked immunosorbent assay. UuLAMPs underwent separation and Western blot analyses.

Results

UuLAMPs (0.025–0.4 µg/ml) stimulated RASF proliferation in a dose- and time-dependent manner, and increased TNF-α and IL-1β levels in THP-1 macrophages. Several immunogenic UuLAMPs were identified, but antibodies to a 25 kDa protein were only found in RA patients with U. urealyticum infection.

Conclusions

UuLAMPs might induce RASF proliferation and proinflammatory cytokine secretion in synovium from RA patients. A 25 kDa U. urealyticum protein might act as a cross-reactive antigen.

Adjuvant engineering for cancer immunotherapy: Development of a synthetic TLR2 ligand with increased cell adhesion

The development of effective immunoadjuvants for tumor immunotherapy is of fundamental importance. The use of Mycobacterium bovis bacillus Calmette-Guérin cell wall skeleton (BCG-CWS) in tumor immunotherapy has been examined in various clinical applications. Because BCG-CWS is a macromolecule that cannot be chemically synthesized, the development of an alternative synthetic molecule is necessary to ensure a constant supply of adjuvant. In the present study, a new adjuvant was designed based on the structure of macrophage-activating lipopeptide (MALP)-2, which is a Toll-like receptor (TLR)-2 ligand similar to BCG-CWS. Macrophage-activating lipopeptide-2, [S-(2,3-bispalmitoyloxypropyl)Cys (P2C) - GNNDESNISFKEK], originally identified in a Mycoplasma species, is a lipopeptide that can be chemically synthesized. A MALP-2 peptide was substituted with a functional motif, RGDS, creating a novel molecule named P2C-RGDS. RGDS was selected because its sequence constitutes an integrin-binding motif and various integrins are expressed in immune cells including dendritic cells (DCs). Thus, this motif adds functionality to the ligand. P2C-RGDS activated DCs and splenocytes more efficiently than MALP-2 over short incubation times in vitro, and the RGDS motif contributed to their activation. Furthermore, P2C-RGDS showed higher activity than MALP-2 in inducing migration of DCs to draining lymph node, and in inhibiting tumor growth in vivo. This process of designing and developing synthetic adjuvants has been named "adjuvant engineering," and the evaluation and improvement of P2C-RGDS constitutes a first step in the development of stronger synthetic adjuvants in the future.

Cytokines in Mycoplasma pneumoniae infections

Mycoplasma pneumoniae (M. pneumoniae) is one of the smallest free-living bacteria known. Along with other unique characteristics of this genus, it lacks the typical peptidoglycan cell wall of most eubacteria. Best known for causing tracheobronchitis and atypical pneumonia in humans, this pathogen also causes a number of extrapulmonary syndromes such as meningitis/encephalitis and arthritis. Recent studies also suggest that infection may be associated with chronic conditions such as asthma. Although the mechanisms of M. pneumoniae pathogenesis remain to be elucidated, one important component of M. pneumoniae infections is the induction of proinflammatory and other cytokines in both acute and chronic conditions. In this review, we survey the induction of cytokines by M. pneumoniae in different model systems, and we discuss the possible role of induced cytokines in M. pneumoniae pathogenesis.

The macrophage-activating lipopeptide-2 accelerates wound healing in diabetic mice

Wound healing in healthy individuals proceeds at an optimal rate. However, in patients, with -- e.g.-- locally impaired blood flow or diabetes, chronic wounds develop and often become infected. Chronic wounds mean a low quality of life for the afflicted patients, not to mention enormous costs. Rather than using recombinant growth factors to accelerate wound healing, we employed the toll-like receptor agonist macrophage-activating lipopeptide-2 (MALP-2) to improve the healing of full-thickness excision skin wounds in an animal model with obese, diabetic mice. A gene array experiment suggested that MALP-2 stimulates the release of various mediators involved in wound healing. Further data to be presented in this study will show (i) that MALP-2 is capable of stimulating the appearance of the monocyte chemoattractant protein-1 at the wound site, (ii) that this leads to increased leucocyte and, in particular, macrophage infiltration and (iii) that MALP-2-treated wounds closed 2 weeks earlier than vehicle-treated controls. MALP-2, thus, appears to stimulate the early inflammatory process needed to set in motion the ensuing consecutive natural steps of wound healing resulting in wound closure.

A lipoprotein family from Mycoplasma fermentans confers host immune activation through Toll-like receptor 2

Mycoplasma have been reported to be associated with human diseases. Three forms of a mycoplasma lipopeptide/protein with the ability to modulate the host immune system were independently identified and named macrophage-activating lipopeptide 2 (MALP-2), P48 and M161Ag (identical to MALP-404). Although these molecules had polypeptides of different sizes, they exerted similar immunomodulatory effects on macrophages/dendritic cells, such as cytokine induction, NO production and maturation of antigen-presenting cells (APCs). M161Ag exhibited complement-activating ability and bound macrophages via complement C3b/C3bi and their receptors. The diacylated N-terminal palmitates were involved in these activities. Toll-like receptor 2 (TLR2) was found to be responsible for these functional features of these mycoplasma products, except for complement activation. Here, we summarize the functional properties of this family of proteins, namely pathogen-associated molecular pattern (PAMP) and discuss its relationship to the reported pathogenesis of latent mycoplasma infection.

Structural-functional relationship of pathogen-associated molecular patterns: lessons from BCG cell wall skeleton and mycoplasma lipoprotein M161Ag

The innate immune system senses microbial components by signaling receptors and induces phagocytosis by uptake receptors. The Toll-like receptor represents the signaling receptors that cause maturation of dendritic cells, while phagocytosis is supported by other receptor families. We identify the structural signatures of microbial components recognized by these receptors to establish the two-receptor hypothesis in innate immunity.

In vivo effects of a synthetic 2-kilodalton macrophage-activating lipopeptide of Mycoplasma fermentans after pulmonary application

Mycoplasmas can cause interstitial pneumonias inducing critical illness in humans and animals. Mycoplasma infections are characterized by an influx of neutrophils, followed by an accumulation of macrophages and lymphocytes. The present study deals with the question of which mycoplasmal components cause this host reaction. The mycoplasma-derived, macrophage-activating lipopeptide 2S-MALP-2 was used to mimic the sequelae of a mycoplasma infection. To this end, 2S-MALP-2 was intratracheally instilled into the lungs of Lewis rats, and the bronchoalveolar lavage cells were examined at different times after different doses of 2S-MALP-2. Application of 2.5 microg induced a pronounced leukocyte accumulation in the bronchoalveolar space. At 24 h after 2S-MALP-2 administration, the majority of leukocytes consisted of neutrophils, followed by macrophages, peaking on days 2 and 3. Lymphocyte numbers, although amounting to only a few percent of the total bronchoalveolar lavage cells, also increased significantly, with maximal lymphocyte accumulation occurring by 72 h after instillation. The leukocyte count of the lung interstitium was increased on day 3 after treatment. After 10 days all investigated cell populations returned to control levels. Transient chemotactic activity for neutrophils was detected in the bronchoalveolar lavage fluid early after 2S-MALP-2 application, followed by monocyte chemoattractant protein-1 activity (MCP-1) in lung homogenates. MCP-1 was produced by bronchoalveolar lavage cells upon stimulation with 2S-MALP-2. Our data indicate that mycoplasmal lipoproteins and lipopeptides are probably the most relevant mycoplasmal components for the early host reaction. The primary target cells are likely to be the alveolar macrophages liberating chemokines, which attract further leukocytes.

Regulation of proinflammatory cytokines in human lung epithelial cells infected with Mycoplasma pneumoniae

Mycoplasma pneumoniae is a small bacterium without a cell wall that causes tracheobronchitis and atypical pneumonia in humans. It has also been associated with chronic conditions, such as arthritis, and extrapulmonary complications, such as encephalitis. Although the interaction of mycoplasmas with respiratory epithelial cells is a critical early phase of pathogenesis, little is known about the cascade of events initiated by infection of respiratory epithelial cells by mycoplasmas. Previous studies have shown that M. pneumoniae can induce proinflammatory cytokines in several different study systems including cultured murine and human monocytes. In this study, we demonstrate that M. pneumoniae infection also induces proinflammatory cytokine expression in A549 human lung carcinoma cells. Infection of A549 cells resulted in increased levels of interleukin-8 (IL-8) and tumor necrosis factor alpha mRNA, and both proteins were secreted into culture medium. IL-1 beta mRNA also increased after infection and IL-1 beta protein was synthesized, but it remained intracellular. In contrast, levels of IL-6 and gamma interferon mRNA and protein remained unchanged or undetectable. Using protease digestion and antibody blocking methods, we found that M. pneumoniae cytoadherence is important for the induction of cytokines. On the other hand, while M. pneumoniae protein synthesis and DNA synthesis do not appear to be prerequisites for the induction of cytokine gene expression, A549 cellular de novo protein synthesis is responsible for the increased cytokine protein levels. These results suggest a novel role for lung epithelial cells in the pathogenesis of M. pneumoniae infection and provide a better understanding of M. pneumoniae pathology at the cellular level.

Site-specific proteolysis of the MALP-404 lipoprotein determines the release of a soluble selective lipoprotein-associated motif-containing fragment and alteration of the surface phenotype of Mycoplasma fermentans

The mature MALP-404 surface lipoprotein of Mycoplasma fermentans comprises a membrane-anchored N-terminal lipid-modified region responsible for macrophage activation (P. F. Mühlradt, M. Kiess, H. Meyer, R. Süssmuth, and G. Jung, J. Exp. Med. 185:1951-1958, 1997) and an external hydrophilic region that contains the selective lipoprotein-associated (SLA) motif defining a family of lipoproteins from diverse but selective prokaryotes, including mycoplasmas (M. J. Calcutt, M. F. Kim, A. B. Karpas, P. F. Mühlradt, and K. S. Wise, Infect. Immun. 67:760-771, 1999). This family generally corresponds to a computationally defined group of orthologs containing the basic membrane protein (BMP) domain. Two discrete lipid-modified forms of the abundant MALP product which vary dramatically in ratio among isolates of M. fermentans occur on the mycoplasma surface: (i) MALP-404, the full-length mature product, and (ii) MALP-2, the Toll-like receptor 2-mediated macrophage-activating lipopeptide containing the N-terminal 14 residues of the mature lipoprotein. The role of posttranslational processing in the biogenesis of MALP-2 from the prototype MALP-404 SLA-containing lipoprotein was investigated. Detergent phase fractionation of cell-bound products and N-terminal sequencing of a newly discovered released fragment (RF) demonstrated that MALP-404 was subject to site-specific proteolysis between residues 14 and 15 of the mature lipoprotein, resulting in the cell-bound MALP-2 and soluble RF products. This previously unknown mechanism of posttranslational processing among mycoplasmas suggests that specific cleavage of some surface proteins may confer efficient "secretion" of extracellular products by these organisms, with concurrent changes in the surface phenotype. This newly identified form of variation may have significant implications for host adaptation by mycoplasmas, as well as other pathogens expressing lipoproteins of the SLA (BMP) family.

Mycoplasma fermentans lipoprotein M161Ag-induced cell activation is mediated by Toll-like receptor 2: role of N-terminal hydrophobic portion in its multiple functions

M161Ag is a 43-kDa surface lipoprotein of Mycoplasma fermentans, serving as a potent cytokine inducer for monocytes/macrophages, maturing dendritic cells (DCs), and activating host complement on affected cells. It possesses a unique N-terminal lipo-amino acid, S:-diacylglyceryl cysteine. The 2-kDa macrophage-activating lipopeptide-2 (MALP-2), recently identified as a ligand for Toll-like receptor 2 (TLR2), is derived from M161Ag. In this study, we identified structural motifs sustaining the functions of M161Ag using wild-type and unlipidated rM161Ag with (SP(+)) or without signal peptides (SP(-)). Because the SP(+) rM161Ag formed dimers via 25Cys, we obtained a monomeric form by mutagenesis (SP(+)C25S). Only wild type accelerated maturation of human DCs as determined by the CD83/86 criteria, suggesting the importance of the N-terminal fatty acids for this function. Wild-type and the SP(+) form of monomer induced secretion of TNF-alpha and IL-12 p40 by human monocytes and DCs. Either lipid or signal peptide at the N-terminal portion of monomer was required for expression of this function. In contrast, murine macrophages produced TNF-alpha in response to wild type, but not to any recombinant form of M161Ag, suggesting the species-dependent response to rM161Ag. Wild-type and both monomeric and dimeric SP(+) forms possessed the ability to activate complement via the alternative pathway. Again, the hydrophobic portion was associated with this function. These results, together with the finding that macrophages from TLR2-deficient mice did not produce TNF-alpha in response to M161Ag, infer that the N-terminal hydrophobic structure of M161Ag is important for TLR2-mediated cell activation and complement activation.

Complement activation in Mycoplasma fermentans-induced mycoplasma clearance from infected cells: probing of the organism with monoclonal antibodies against M161Ag

Mycoplasma fermentans, a cell wall-less prokaryote, is capable of infecting humans and has been suggested to serve as a cofactor in AIDS development. Recently, we discovered a novel lipoprotein with a molecular mass of 43 kDa originating from M. fermentans. This protein, named M161Ag, activated human complement via the alternative pathway and efficiently induced the proinflammatory cytokines interleukin 1beta (IL-1beta), tumor necrosis factor alpha, IL-6, IL-10, and IL-12 in human peripheral blood monocytes. It is likely that M161Ag of M. fermentans affects the host immune system upon mycoplasma infection. In this study, we developed monoclonal antibodies (MAbs) against M161Ag and examined the direct role of complement in M. fermentans infection using these MAbs as probes. M. fermentans was rapidly cleared from the surfaces of infected cells by human complement, but a low-grade infection persisted in human tumor cell lines. Mycoplasma particles remaining alive in host cells may cause recurrent infection, and liberated M161Ag may serve as a biological response modifier affecting both innate and acquired immunity.

Expression and antigenic characterization of recombinant Mycoplasma agalactiae P48 major surface protein

The gene encoding the P48 major surface lipoprotein of M. agalactiae has been recently characterised. Since its product plays an important role in the immune response of infected animals, in this study we analysed a recombinant P48 expressed in E. coli. Multiple point mutations were introduced by site directed mutagenesis in order to convert four tryptophan TGA codons, which are a typical feature of the mycoplasma genetic code, into the standard TGG. The mutated p48 gene was subcloned into pGex-2T and expressed in fusion with glutathione-S transferase. Following purification steps, P48 was eluted from carrier protein by thrombin digestion and used in Western blot and indirect ELISA using well-characterised sheep sera. Results demonstrate that specific antibodies against P48 are detected 3 weeks after onset of clinical disease and the recombinant P48 is a diagnostically relevant marker of M. agalactiae infection.

Partial purification and characterization of the active entity responsible for inducing interleukin-6 production by human gingival fibroblasts from Mycoplasma salivarium cells

The active entity responsible for inducing interleukin-6 production by human gingival fibroblasts was partially purified by ion-exchange chromatography from the water-soluble fraction of Mycoplasma salivarium cells. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the final preparation revealed one densely stained band with a molecular weight of 20.6 kilodaltons and two faint bands with molecular weights of 40.5 and 82.5 kilodaltons. The specific activity of the final preparation was 34-fold higher than that of the starting water-soluble fraction. The interleukin-6-inducing activity was destroyed by proteinase K and reduced 70% by lipoprotein lipase and heat treatment, but was not affected by deoxyribonuclease I or endoglucosidase D. The final preparation induced small amounts of tumor necrosis factor-alpha and interleukin-lbeta in a myelomonocytic cell line, THP-1 cells, but did not induce interleukin-6. The ability of Escherichia coli lipopolysaccharide to stimulate human gingival fibroblasts to release interleukin-6 was dependent upon the presence of serum in the assay medium, but that of the final preparation from M. salivarium was not. Thus, we partially purified the protein(s) from M. salivarium which were capable of stimulating human gingival fibroblasts to release interleukin-6 by a mechanism different from that of E. coli lipopolysaccharide.

P48 major surface antigen of Mycoplasma agalactiae is homologous to a malp product of Mycoplasma fermentans and belongs to a selected family of bacterial lipoproteins

A major surface antigenic lipoprotein of Mycoplasma agalactiae, promptly recognized by the host's immune system, was characterized. The mature product, P48, showed significant similarity and shared conserved amino acid motifs with lipoproteins or predicted lipoproteins from Mycoplasma fermentans, Mycoplasma hyorhinis, relapsing fever Borrelia spp., Bacillus subtilis, and Treponema pallidum.

Mycoplasmal lipopeptide MALP-2 induces the chemoattractant proteins macrophage inflammatory protein 1alpha (MIP-1alpha), monocyte chemoattractant protein 1, and MIP-2 and promotes leukocyte infiltration in mice

Natural as well as experimental infections with pathogenic mycoplasmas lead to cellular responses characterized by early polymorphonuclear leukocyte influx, which in turn is followed by infiltration of macrophages. Since some of the most potent leukocyte chemoattractants are macrophage products, we investigated whether the 2-kDa macrophage-activating lipopeptide (MALP-2) from Mycoplasma fermentans was capable of inducing chemoattractant chemokines and initiating an in vivo inflammatory effect. MALP-2 was a potent in vitro inducer of the chemokines macrophage inflammatory protein 1alpha (MIP-1alpha), monocyte chemoattractant protein 1 (MCP-1), and MIP-2, yielding a maximal response at 0.1 ng/ml (5 x 10(-11) M). Leukocyte infiltration was determined after intraperitoneal injection of MALP-2, liposome-encapsulated MALP-2, and heat-killed mycoplasmas. There was a steady increase in the number of peritoneal cells over 72 h in response to these agents. Polymorph counts were maximal by 24 to 48 h, decreasing thereafter. Monocytes/macrophages had significantly increased after 3 days. MIP-1alpha, MCP-1, and MIP-2 levels in serum or peritoneal lavage fluid were determined. MIP-1alpha and MCP-1 levels were elevated by 2 to 6 h after injection and were still above control values after 24 h. In contrast, MIP-2 levels reached their maximum at 2 h, dropping to control values after 24 h. We conclude that macrophage-stimulating mycoplasmal lipoproteins, exemplified by MALP-2, play an important role in the late phase of phagocyte recruitment at sites of infection and that this is affected by leukoattractive chemokines.

Antibody-independent classical complement pathway activation and homologous C3 deposition in xeroderma pigmentosum cell lines

Of human malignantly transformed cell lines, xeroderma pigmentosum (XP) cell lines were found to be highly susceptible to homologous complement (C): cells were opsonized by C3 fragments on incubation with diluted normal human serum. C3 fragment deposition on XP cells was Ca2+-dependent and occurred on live cells but not UV-irradiated apoptotic cells. (Ca2+ is required for activation of the classical C pathway via C1q and the lactin pathway via mannose binding lectin (MBL), and the surface of apoptotic cells usually activates the alternative C pathway.) In this study we tested which of the pathways participates in XP cell C3 deposition. In seven cell lines that allowed C3 deposition (i), Clq was shown to be essential but MBL played no role in C activation, (ii) Cls but not MASP bound XP cells for activation, (iii) no antibodies recognizing XP cells were required for homologous C3 deposition, and (iv) the alternative pathway barely participated in C3 deposition. Furthermore, the levels of C-regulatory proteins for host cell protection against C, decay-accelerating factor (DAF, CD55) and membrane cofactor protein (MCP, CD46), were found to be relatively low in almost all XP cell lines compared with normal cells. These results indicate that XP cells activate the classical C pathway in an antibody-independent manner through the expression of a molecule which directly attracts C1q in a C-activating form, and that relatively low levels of DAF and MCP on XP cells facilitate effective C3 deposition. The possible relationship between the pathogenesis of XP and our findings is discussed.

Differential posttranslational processing confers intraspecies variation of a major surface lipoprotein and a macrophage-activating lipopeptide of Mycoplasma fermentans

The malp gene of Mycoplasma fermentans is shown to occur in single copy but to encode two discrete translated forms of lipid-modified surface protein that can be differentially expressed on isolates within this species: MALP-2, a 14-amino-acid (2-kDa) lipopeptide with potent macrophage-stimulatory activity (P. F. Mühlradt, M. Kiess, H. Meyer, R. Süssmuth, and G. Jung, J. Exp. Med. 185:1951-1958, 1997), and MALP-404, an abundant, full-length (404-amino-acid) surface lipoprotein of 41 kDa, previously designated P41 (K. S. Wise, M. F. Kim, P. M. Theiss, and S.-C. Lo, Infect. Immun. 61:3327-3333, 1993). The sequences, transcripts, and translation products of malp were compared between clonal isolates of strains PG18 (known to express P41) and II-29/1 (known to express high levels of MALP-2). Despite conserved malp DNA sequences containing full-length open reading frames and expression of full-length monocistronic transcripts in both isolates, Western blotting using a monoclonal antibody (MAb) to the N-terminal MALP-2 peptide revealed marked differences in the protein products expressed. Whereas PG18 expressed abundant MALP-404 with detectable MALP-2, II-29/1 revealed no MALP-404 even in samples containing a large comparative excess of MALP-2. Colony immunoblots with the MAb showed uniform surface expression of MALP-2 in II-29/1 populations. A second MAb to an epitope of MALP-404 outside the MALP-2 sequence predictably failed to stain II-29/1 colonies but uniformly stained PG18 populations. Collectively, these results provide evidence for novel posttranscriptional (probably posttranslational) processing pathways leading to differential intraspecies expression of a major lipoprotein, and a potent macrophage-activating lipopeptide, on the surface of M. fermentans. In the course of this study, a striking conserved motif (consensus, TD-G--DDKSFNQSAWE--), designated SLA, was identified in MALP-404; this motif is also distributed among selected lipoproteins and species from diverse bacterial genera, including Bacillus, Borrelia, Listeria, Mycoplasma, and Treponema. In addition, malp was shown to flank a chromosomal polymorphism. In eight isolates of M. fermentans examined, malp occurred upstream of an operon encoding the phase-variable P78 ABC transporter; but, in three of these isolates, a newly discovered insertion sequence, IS1630 (of the IS30 class), was located between these genes.