Detection of serum antibodies against phosphocholine-containing aminoglycoglycerolipid specific to Mycoplasma fermentans in HIV-1 infected individuals

Association of Mycoplasma fermentans and the risk of HIV-1 infection: A meta-analysis

BACKGROUND

Previous studies have reported the association between Mycoplasma fermentans (M. fermentans) and the risk of human immunodeficiency virus 1 (HIV-1) infection, but the results were inconsistent. The present study aims to systematically review reported studies on M. fermentans and its association with HIV-1 infection, as well as to summarize the findings using a meta-analysis.

METHODS

Studies meeting the inclusion criteria in the PubMed, Embase, China National Knowledge Infrastructure, WanFang Data, and Chongqing VIP databases up to March 2019 were identified. Cochran Q and I statistics were used to assess heterogeneity. Additionally, pooled odds ratio (OR) with 95% confidence intervals (CI) were calculated and displayed by Forest plots. Also, the funnel plot, Begg test, and Egger test were used to evaluate potential publication bias. In addition, the source of heterogeneity was investigated by subgroup and sensitivity analyses.

RESULTS

A total of 11 studies comprising 1028 HIV-1-positive patients and 1298 controls were ultimately included in this meta-analysis. Our results indicated that M. fermentans could increase the risk of HIV-1 infection among humans (OR = 3.66, 95%CI 1.26-10.64). Subgroup analysis showed that the risk of HIV-1 infection associated with M. fermentans was, based on the geographical distribution, 1.19 (95%CI 0.33-4.33) in Europe, 2.83 (95%CI 0.94-8.52) in United States, 11.92 (95%CI 3.93-36.15) in Asia; based on the source of the sample, 2.97 (95%CI 0.89-9.95) in blood samples, 4.36 (95%CI 1.63-11.68) in urine samples; based on the detection method, 2.80 (95%CI 0.72-10.96) with the polymerase chain reaction method, 5.54 (95%CI 1.21-25.28) with other detection methods; based on the source of controls, 1.91 (95%CI 0.53-6.89) in sexually transmitted diseases individuals, and 8.25 (95%CI 2.16-31.60) in health individuals.

CONCLUSION

Our study revealed evidence of the association between M. fermentans and HIV-1 infection. Considering the heterogeneity, further studies are warranted to understand the relationship between M. fermentans and HIV-1 infection.

TLC immunostaining for detection of "antiphospholipid" antibodies

Thin-layer chromatography (TLC) is a nonquantitative technique, which has been employed in the detection of antiphospholipid (aPL) antibodies. Antiphospholipid syndrome (APS) is the most frequently acquired thrombophilia, characterized by thrombosis and obstetric manifestations associated to an autoimmune trait, represented by the positivity of antiphospholipid (aPL) antibodies. Immunoassays for anticardiolipin (aCL) and anti-β2 glycoprotein I (aβ2GPI) antibodies and clotting tests for lupus anticoagulant (LA) represent the standard tests for the routine detection of aPL. The term "seronegative APS" has been used to describe patients with clinical manifestation of APS and persistently negative aPL assessed with routine assays. TLC immunostaining is a useful method for the detection of different antigenic targets of "antiphospholipid" antibodies; it is able to identify the reactivity of serum aPL experimented with purified phospholipid molecules with a different exposure compared to ELISA methods. This method seems to be applicable in patients who repeatedly tested negative for the standard aPL, i.e., aCL, aβ2GPI, and LA. Therefore, this technique may be proposed as a second step test for the diagnosis of APS.

O-linked protein glycosylation in Mycoplasma

Although mycoplasmas have a paucity of glycosyltransferases and nucleotidyltransferases recognizable by bioinformatics, these bacteria are known to produce polysaccharides and glycolipids. We show here that mycoplasmas also produce glycoproteins and hence have glycomes more complex than previously realized. Proteins from several species of Mycoplasma reacted with a glycoprotein stain, and the murine pathogen Mycoplasma arthritidis was chosen for further study. The presence of M. arthritidis glycoproteins was confirmed by high-resolution mass spectrometry. O-linked glycosylation was clearly identified at both serine and threonine residues. No consensus amino acid sequence was evident for the glycosylation sites of the glycoproteins. A single hexose was identified as the O-linked modification, and glucose was inferred by (13) C-labelling to be the hexose at several of the glycosylation sites. This is the first study to conclusively identify sites of protein glycosylation in any of the mollicutes.

Rhamnose biosynthesis in mycoplasmas requires precursor glycans larger than monosaccharide

Despite the apparent absence of genes coding for the known pathways for biosynthesis, the monosaccharide rhamnose was detected in the d configuration in Mycoplasma pneumoniae and Mycoplasma pulmonis, and in both the d and l configurations in Mycoplasma arthritidis. Surprisingly, the monosaccharide glucose was not a precursor for rhamnose biosynthesis and was not incorporated at detectable levels in glucose-containing polysaccharides or glycoconjugates. In contrast, carbon atoms from starch, a polymer of glucose, were incorporated into rhamnose in each of the three species examined. When grown in a serum-free medium supplemented with starch, M. arthritidis synthesized higher levels of rhamnose, with a shift in the relative amounts of the d and l configurations. Our findings suggest the presence of a novel pathway for rhamnose synthesis that is widespread in the genus Mycoplasma.

An easy α-glycosylation methodology for the synthesis and stereochemistry of mycoplasma α-glycolipid antigens

Mycoplasma fermentans possesses unique α-glycolipid antigens (GGPL-I and GGPL-III) at the cytoplasm membrane, which carry a phosphocholine group at the sugar primary (6-OH) position. This paper describes a practical synthetic pathway to a GGPL-I homologue (C(16:0)) and its diastereomer, in which our one-pot α-glycosylation method was effectively applied. The synthetic GGPL-I isomers were characterized with (1)H NMR spectroscopy to determine the equilibrium among the three conformers (gg, gt, tg) at the acyclic glycerol moiety. The natural GGPL-I isomer was found to prefer gt (54%) and gg (39%) conformers around the lipid tail, while adopting all of the three conformers with equal probability around the sugar position. This property was very close to what we have observed with respect to the conformation of phosphatidylcholine (DPPC), suggesting that the Mycoplasma glycolipids GGPLs may constitute the cytoplasm fluid membrane together with ubiquitous phospholipids, without inducing stereochemical stress.

Promotion of arthritis and allergy in mice by aminoglycoglycerophospholipid, a membrane antigen specific to Mycoplasma fermentans

Mycoplasmas, which lack a cell wall and are the smallest self-replicating bacteria, have been linked to some chronic diseases, such as AIDS, rheumatoid arthritis (RA), and oncogenic transformation of cells. Their membrane components (lipoproteins and glycolipids) have been identified as possible causative factors in such diseases. Glycoglycerophospholipid (GGPL)-III, a unique phosphocholine-containing aminoglycoglycerophospholipid, is a major specific antigen of Mycoplasma fermentans, and has been detected in 38% of RA patients. Unlike those of lipoproteins, which induce inflammation via Toll-like receptor 2 (TLR2), the pathologic effects of GGPL-III are poorly understood. RA and metal allergies are chronic inflammatory diseases in which autoantigens have been implicated. Here, we examined the effects of chemically synthesized GGPL-III in murine arthritis and allergy models. GGPL-III alone exhibited little inflammatory effect, but promoted both collagen-induced arthritis and nickel (Ni) allergy, although less powerfully than Escherichia coli lipopolysaccharide. The augmenting effect of GGPL-III on Ni allergy was present in mice deficient in either T cells or active TLR4, but it was markedly weaker in mice deficient in macrophages, interleukin-1, or the histamine-forming enzyme histidine decarboxylase than in their control strains. These results suggest that GGPL-III may play roles in some types of chronic diseases via the innate immune system.

Physicochemical characterization and biological activity of a glycoglycerolipid from Mycoplasma fermentans

We report a comprehensive physicochemical characterization of a glycoglycerolipid from Mycoplasma fermentans, MfGl-II, in relation to its bioactivity and compared this with the respective behaviors of phosphatidylcholine (PC) and a bacterial glycolipid, lipopolysaccharide (LPS) from deep rough mutant Salmonella minnesota strain R595. The beta left arrow over right arrow alpha gel-to-liquid crystalline phase transition behavior of the hydrocarbon chains with Tc = 30 degrees C for MfGl-II as well as for LPS exhibits high similarity between the two glycolipids. A lipopolysaccharide-binding protein (LBP)-mediated incorporation into negatively charged liposomes is observed for both glycolipids. The determination of the supramolecular aggregate structure confirms the existence of a mixed unilamellar/cubic structure for MfGl-II, similar to that observed for the lipid A moiety of LPS. The biological data clearly show that MfGl-II is able to induce cytokines such as tumor necrosis factor-alpha (TNF-alpha) in human mononuclear cells, although to a significantly lower degree than LPS. In contrast, in the Limulus amebocyte lysate test, MfGl-II is completely inactive, and in the CHO reporter cell line it does not indicate any reactivity with the Toll-like receptors TLR-2 and -4, in contrast to control lipopeptides and LPS. These data confirm the applicability of our conformational concept of endotoxicity to nonlipid A structures: an amphiphilic molecule with a nonlamellar cubic aggregate structure corresponding to a conical conformation of the single molecules and a sufficiently high negative charge density in the backbone.

Choline-containing lipids in mycoplasmas

Choline-containing lipids were identified and characterized in the cell membrane of Mycoplasma fermentans and were shown to participate in the adhesion to the surface of eukaryotic cells, to stimulate mycoplasma fusion with eukaryotic cells, and to induce cytokine secretion by cells of the immune system. These findings suggest that choline-containing lipids are important mediators of tissue pathology in the infectious process caused by M. fermentans.

Monoclonal antibody against Mycoplasma fermentans-specific aminoglycoglycerolipid

Previously, we reported that Mycoplasma fermentans has specific antigens (phosphocholine-containing glycoglycerolipids: GGPL-I and GGPL-III) and discussed the possibility of their pathogenic role. In this paper, we report the characterization of a monoclonal antibody (MF-III-1) specific to GGPL-III (phosphocholine-containing aminoglycoglycerolipid) using methods of electron microscopy, immunofluorescence cell surface staining, laser scanning microscopy, immunoelectron microscopy, and thin-layer chromatography immunostaining. The MF-III-1 antibody specifically recognized M. fermentans attached to the surface of HTLV-I-infected human helper T-cells, and it did not cross-react with other lipids nor with human T-cell antigens. Since MF-III-1 distinguishes GGPL-III from GGPL-I, the binding site may include a serinol (2-amino-1,3-propanediol) residue of GGPL-III. MF-III-1 is useful for the in vitro study of M. fermentans, and may also be useful as a tool for the study of the involvement of M. fermentans in human diseases.

Ether lipids in the cell membrane of Mycoplasma fermentans

Two new ether lipids, 1-O-alkyl/alkenyl-2-O-acyl-glycero-3-phosphocholine and its lyso form, 1-O-alkyl/alkenyl-glycero-3-phosphocholine, were identified in the cell membrane of Mycoplasma fermentans using chemical analyses, GLC-MS, MALDI-TOF MS, and 1D and 2D NMR spectroscopy. The lipids are heterogeneous with respect to both acyl and alkyl/alkenyl residues. The acyl residues at position 2 of glycerol are hexadecanoyl and octadecanoyl in a molar ratio of 3.6 : 1 with a trace amount of octadecenoyl. The alkyl/alkenyl residues at position 1 of glycerol are hexadecyl (78%), octadecyl (7%), octadecenyl (14%), and hexadecenyl (traces). In the octadecenyl residue, the double bond has a cis configuration and is located at either position 1' (plasmalogen-type lipid) or 9' in a ratio approximately 1 : 1. This is the first report of the presence of alkyl and vinyl (alk-1'-enyl) ether lipids in the cell membrane of aerobically grown mycoplasmas. Lipids of this type have been found in some Gram-positive bacteria, thus supporting the hypothesized close taxonomical relationship of these bacteria to mycoplasmas. The ether lipids of M. fermentans are structurally similar to platelet activating factor; it was demonstrated that the 2-O-acetylated lyso form lipid can mimic platelet-activating factor activity in isolated perfused and ventilated rat lungs.