Partial biochemical characterization of spiroplasma membrane component inducing tumor necrosis factor alpha

Molecular biology and pathogenicity of mycoplasmas

The recent sequencing of the entire genomes of Mycoplasma genitalium and M. pneumoniae has attracted considerable attention to the molecular biology of mycoplasmas, the smallest self-replicating organisms. It appears that we are now much closer to the goal of defining, in molecular terms, the entire machinery of a self-replicating cell. Comparative genomics based on comparison of the genomic makeup of mycoplasmal genomes with those of other bacteria, has opened new ways of looking at the evolutionary history of the mycoplasmas. There is now solid genetic support for the hypothesis that mycoplasmas have evolved as a branch of gram-positive bacteria by a process of reductive evolution. During this process, the mycoplasmas lost considerable portions of their ancestors' chromosomes but retained the genes essential for life. Thus, the mycoplasmal genomes carry a high percentage of conserved genes, greatly facilitating gene annotation. The significant genome compaction that occurred in mycoplasmas was made possible by adopting a parasitic mode of life. The supply of nutrients from their hosts apparently enabled mycoplasmas to lose, during evolution, the genes for many assimilative processes. During their evolution and adaptation to a parasitic mode of life, the mycoplasmas have developed various genetic systems providing a highly plastic set of variable surface proteins to evade the host immune system. The uniqueness of the mycoplasmal systems is manifested by the presence of highly mutable modules combined with an ability to expand the antigenic repertoire by generating structural alternatives, all compressed into limited genomic sequences. In the absence of a cell wall and a periplasmic space, the majority of surface variable antigens in mycoplasmas are lipoproteins. Apart from providing specific antimycoplasmal defense, the host immune system is also involved in the development of pathogenic lesions and exacerbation of mycoplasma induced diseases. Mycoplasmas are able to stimulate as well as suppress lymphocytes in a nonspecific, polyclonal manner, both in vitro and in vivo. As well as to affecting various subsets of lymphocytes, mycoplasmas and mycoplasma-derived cell components modulate the activities of monocytes/macrophages and NK cells and trigger the production of a wide variety of up-regulating and down-regulating cytokines and chemokines. Mycoplasma-mediated secretion of proinflammatory cytokines, such as tumor necrosis factor alpha, interleukin-1 (IL-1), and IL-6, by macrophages and of up-regulating cytokines by mitogenically stimulated lymphocytes plays a major role in mycoplasma-induced immune system modulation and inflammatory responses.

Mycoplasma hyorhinis molecules that induce tumor necrosis factor alpha secretion by human monocytes

Mycoplasma hyorhinis has been shown to induce the secretion of tumor necrosis factor alpha (TNF-alpha) from monocytes. To identify the molecules responsible for this activity, we separated sonicated M. hyorhinis lysate material by centrifugation at 100,000 x g into soluble (S) and particulate (P) fractions. The fractions were assayed for TNF-alpha-inducing activity by the L929 bioassay. Both the soluble and particulate fractions were able to induce TNF-alpha in roughly equal amounts. The optimum dose for both fractions was 1 micrograms/ml. Proteinase K treatment of either fraction eliminated the activity, suggesting that a protein component is involved in induction. Phase partitioning into Triton X-114 aqueous (A) and detergent (D) phases showed that the soluble fraction was composed of 80% aqueous-phase proteins, while the particulate fraction was > 75% detergent-phase proteins. All four fractions (SA, SD, PA, and PD) were able to induce TNF-alpha release. Treatment with NaIO4 to remove carbohydrate reduced the inducing activity of the SA phase by 80%, whereas that of the other fractions was unaffected by this treatment. The M(r)S of the inducing activity were determined by the monocyte Western (immunoblot) technique. The SA phase activity was associated with a single periodate-sensitive peak of 69 to 75 kDa. The two detergent phases had similar profiles of inducing activity, containing four peaks of activity. These peaks corresponded to 48 to 52, 43 to 45, 39 to 40, and 31 to 32 kDa. The PA fraction also contained four peaks of activity, 69 to 75, 55 to 57, 48 to 52, and 39 to 40 kDa. Thus, both a protein and glycan moiety from M. hyorhinis are capable of inducing TNF-alpha release from human monocytes.

A 48-kilodalton Mycoplasma fermentans membrane protein induces cytokine secretion by human monocytes

Mycoplasma fermentans is one of several Mycoplasma species that have been reported to stimulate tumor necrosis factor (TNF) secretion from monocytes. This activity has been associated primarily with the mycoplasma membrane fraction. In this article, we have characterized a membrane protein that stimulates TNF and interleukin 1 beta secretion. The TNF-releasing activity partitioned into the Triton X-114 detergent phase, suggesting that the molecules is hydrophobic. The secretion of TNF is elevated in the presence of serum, which suggests that a serum component may play a role in the interaction between this mycoplasma protein and monocytes. Treatment of monocytes with monoclonal anti-CD14 antibody had no effect on the levels of TNF-releasing activity. By using the monocyte Western blot (immunoblot) technique, we have determined the molecular mass of the active molecule to be 48 kDa. This molecule appears to be distinct from the recently described family of variable lipoproteins of M. fermentans. Mycoplasma particulate material treated with proteinase K lost all inducing activity, whereas lipoprotein lipase-treated samples retained some level of activity.

Characterization and purification of a mycoplasma membrane-derived macrophage-activating factor

A highly hydrophobic component derived from the membrane of Mycoplasma capricolum has been characterized, purified and assessed for its ability to activate macrophages to tumor cytotoxicity. Initially, crude membranes were evaluated for their solubility in a wide range of solvents. Despite differential solubility in the various solvents, the mycoplasma membranes retained their ability to potentiate macrophage tumor cytotoxicity. Mycoplasma membranes were further characterized by appraising their macrophage-activating ability subsequent to various chemical treatments: cleavage of ester and thioester bonds, oxidation of vicinal hydroxyl groups, and exposure to a broad range of pH. Only strong alkaline treatment (pH > 12) caused a reduction in mycoplasma membrane activity; all other chemical treatments were inconsequential. With potential therapeutic applications in mind, mycoplasma membranes were subjected to various physical treatments including heating, freezing/thawing, sonication, lyophilization and storage. The ability of the membranes to induce macrophage activation was stably maintained following all these treatments. Purification of membranes was initiated by a chloroform/methanol lipid extraction. Macrophage-activating ability was found predominantly in the interphase. Proteolytic cleavage with trypsin increased specific activity at least sixfold. Trypsinized fractions were solubilized in 2-chloroethanol and gel filtration was performed on a hydroxylated Sephadex LH-60 column. The active fraction from this column had a further tenfold increase in specific activity. Subsequent rounds of reverse-phase HPLC on this fraction yielded three to four peaks absorbing at 280 nm, of which only one had macrophage-activating ability.

MDHM, a macrophage-activating product of Mycoplasma fermentans, stimulates murine macrophages to synthesize nitric oxide and become tumoricidal

In continuation of previous work on macrophage activation by a Mycoplasma fermentans-derived product, originally named "mycoplasma-derived high mol. wt. material" (MDHM), we have investigated whether MDHM was capable of inducing synthesis of the reactive nitrogen intermediate nitric oxide (NO), thus rendering macrophages cytocidal. Mycoplasmas were first delipidated with acetone, and MDHM activity was then extracted with 50 mM 1-O-octyl-beta-D-glucopyranoside to yield a particularly active new preparation of MDHM which we have named MDHM-D (D for detergent). In combination with IFN-gamma, MDHM-D activated macrophages to produce reactive nitrogen intermediates and kill P815 mastocytoma cells in co-culture. P815 target cells were chosen because they are TNF-resistant. Macrophages from the LPS-low responder strain C3H/HeJ were used to minimize interference from possible LPS contamination. MDHM-D activity in this system was strictly IFN-gamma-dependent. In the presence of 25 U/ml IFN-gamma MDHM-D gave a half maximal response at a dilution of 1/100,000, showing a parallel concentration dependency for nitrite production and cytocidal activity.