Enhancement of immunoglobulin secretion by the lymphokine-like activity of a Mycoplasma arginini strain

Contamination with Mycoplasma spp. induces interleukin-13 expression by human skin fibroblasts in culture

The mycoplasmas comprise a discrete group of microorganisms that are known to exert a range of effects upon cells derived from the immune system. Some of these interactions turn out to be immunomodulatory, such as polyclonal stimulation of T and B cells or enhancement of the cytolytic potential of macrophages, NK cells and T lymphocytes. Immunologically committed cells, when infected with mycoplasmas, can also increase the production of cytokines (IL-1, IL-2, IL-4 and IL-6), interferon (IFN) gamma, tumor necrosis factor-alpha (TNF-alpha) and colony-stimulating factors (particularly GM-CSF). Moreover, mycoplasmas are potent inductors of cytokine secretion by fibroblasts in culture. Since growth factors are determinants for the activation and proliferation of immunocompetent cells in vitro, we decided to investigate if these effects are concordant with the finding of mycoplasma contamination. In order to address this question, we compared the pattern of lymphokine secretion by normal-derived human fibroblasts in culture with and without Mycoplasma spp. contamination. We found those human fibroblasts that have been contaminated with mycoplasma show production of IL-13 at the transcriptional level. This effect coincides with discrete morphological changes as compared to uncontaminated human fibroblasts. This is the first report to acknowledge that mycoplasma contamination can induce mRNA expression for IL-13 in cultured human fibroblasts.

Mycoplasma arginini TUH-14 membrane lipoproteins induce production of interleukin-1, interleukin-6, and tumor necrosis factor alpha by human monocytes

Mycoplasma arginini TUH-14 partially purified membrane lipoproteins (TUH-14-pp) directly induce secretion of the cytokines involved in the inflammatory response, namely, interleukin 1 (IL-1), tumor necrosis factor alpha, and IL-6, by human monocytes cultured in the absence of serum. The biological activity of each cytokine correlates with its immunoreactivity. Upon stimulation with either TUH-14-pp or lipopolysaccharide, most tumor necrosis factor alpha and IL-6 is secreted in the extracellular compartment, whereas a significant amount of IL-1 remains cell associated. Finally, polymyxin B does not affect secretion of cytokines induced by TUH-14-pp, indicating that mycoplasma lipopolysaccharide does not account for their effects on monocytes. Altogether, our data show that direct interaction of mycoplasma membrane components with human blood monocytes induces secretion of high levels of cytokines known to trigger inflammatory responses. This new concept of membrane-bound active components of mycoplasma may explain its ability to efficiently initiate inflammatory reactions.

Detection of mycoplasma contamination through modulation (stimulation or inhibition) of thymidine incorporation by unstimulated mouse spleen cells

In the present report we describe a rapid and sensitive assay for mycoplasma detection in cell cultures. The assay is based on the ability of contaminated culture supernatants to modulate [3H]TdR incorporation by unstimulated mouse splenocytes. Several mycoplasma species (Mycoplasma orale, culturable and non-culturable strains of Mycoplasma hyorhinis) inhibited [3H]TdR incorporation and permitted the detection of some contaminated cell cultures that would otherwise have escaped detection in assays measuring [3H]TdR incorporation by mitogen-stimulated splenocytes. On the other hand, several other mycoplasma species (Mycoplasma arginini, Mycoplasma hominis) strongly enhanced [3H]TdR incorporation by unstimulated splenocytes. This enhancement was optimally detectable on day 2 after initiation of the cultures. The sensitivity of the assay was determined for a mycoplasma species (culturable M. hyorhinis) that inhibited as well as for one (M. arginini) that enhanced [3H]TdR incorporation. In both cases, the sensitivity was such that 1-3 x 10(2) mycoplasma colony-forming units (CFU) could be detected.

Macrophage-activating factor extracted from mycoplasmas

Mycoplasmas (M. gallisepticum, chicken mycoplasmas), in concert with interferon gamma (IFN gamma), were effective in activating macrophages (M theta) to be tumoricidal. The M theta-activating capacity of mycoplasmas was maintained after treatment with heat. 0.1 M NaOH, 1 M HCl, or trypsin. M theta-activating factor was extracted from mycoplasmas with chloroform/methanol and water (Mf-B). Mf-B was also effective in activating M theta in the presence of IFN gamma. The threshold dose of Mf-B for M theta of ordinary C3H/He mice and that for those of C3H/HeJ mice, the latter being known to be low responders to bacterial lipopolysaccharide, were actually the same. This seems to indicate that the effectiveness of Mf-B was not attributable to possibly contaminating lipopolysaccharides, and that the pathway of activity of Mf-B is different from that of lipopolysaccharides. Since the M theta-activating principle was only a very small part of Mf-B, we have not yet succeeded in identifying it, but there was no evidence that it was protein, nucleic acid, sugar, or lipid. The cytotoxicity of M theta activated by Mf-B plus IFN gamma was dependent on L-arginine in the culture, suggesting that arginine metabolites are involved in M theta cytotoxicity. Mf-B induced a small amount of tumor necrosis factor in M theta, and this induction was markedly enhanced by IFN gamma.

Differential induction of bone marrow macrophage proliferation by mycoplasmas involves granulocyte-macrophage colony-stimulating factor

We have studied the ability of three different Mycoplasma species to induce proliferation of bone marrow-derived macrophages (BMM). We observed a significant mitogenic effect when BMM cells from BALB/c, DBA/2J, SJL, and C57BL/6 mice were incubated with membranes derived from Mycoplasma arginini or M. arthritidis but not when they were incubated with an equivalent amount of M. pulmonis membrane. We also determined that pretreatment of mycoplasma membrane preparations with papain eliminated the ability of these preparations to induce BMM proliferation. To determine whether these membrane fractions acted indirectly by stimulating the production of soluble factors known to stimulate proliferation of BMM cells, we performed blocking studies with antibodies directed against colony-stimulating factor 1 (CSF-1), interleukin-3 (IL-3), and granulocyte-macrophage colony-stimulating factor. Our results indicate that antibodies directed against either CSF-1 or IL-3 failed to block mycoplasma-initiated proliferation of BMM cells. However, when anti-GM-CSF was added to proliferative cultures at the time of initiation, we saw a dose-dependent reduction of mycoplasma-initiated proliferation. We conclude that the ability of mycoplasma membranes to initiate the proliferation of BMM is not shared by all species of mycoplasma and that it involves the production of GM-CSF by an as yet undetermined cell.

Enhancement of cytotoxicity of active macrophages by mycoplasma: role of mycoplasma-associated induction of tumor necrosis factor-alpha (TNF-alpha) in macrophages

Tumor necrosis factor-alpha (TNF-alpha)-inducing activity of several mycoplasmas including Mycoplasma pneumoniae, a causative agent in human respiratory infectious diseases, was investigated. Purified peritoneal macrophages from BALB/c mice markedly enhanced their cytotoxic activity to Meth A cells, when cultured with either viable or non-viable mycoplasmas. The supernatants of the macrophage culture with mycoplasmas, M. pneumoniae and Acholeplasma laidlawii, showed the potent cytotoxic activity to TNF-alpha-sensitive L cells but not to TNF-alpha-insensitive L cells. Addition of anti-TNF-alpha antiserum inhibited completely the cytotoxic activity of these supernatants, indicating that a major part of the cytotoxic activity might be due to TNF-alpha. Various other mycoplasmas, either glucose- or arginine-utilizing species, as far as tested showed also the potent activity to produce TNF-alpha. These results strongly suggest the possibility that mycoplasmas possess the activity of TNF-alpha induction which might be responsible for a part of enhancement of cytotoxic activity of macrophages and resistance to infection with mycoplasmas in vivo.

Interactions between mycoplasmas and the immune system

Mycoplasmas are a heterogenous group of prokaryotic organisms causing a wide variety of diseases, including autoimmune disorders. Thus, it is not surprising that various mycoplasmas strains, including Mycoplasma arginini, M. arthritidis, M. neurolyticum and M. pulmonis, are able to regulate the immune response. Though some of the studies of the immunomodulatory action of mycoplasmas have been done in vivo, the majority of the investigations have been conducted in vitro. This has led to the recognition that mycoplasmas are polyclonal activators of both B and T cells from several species, acting through MHC-restricted or -unrestricted pathways. Mycoplasma activation not only induces T-cell proliferation but also leads but to the formation of cytotoxic T cells. We, as well as others, have shown that mycoplasma-mediated B-cell activation induces proliferation as well as Ig secretion, and also that mycoplasma stimulation of lymphocytes may result in the production of cytokines. We communicate here our investigations into the effects of an M. arginini strain on the growth and maturation of preactivated B cells. After an initial biological characterization of the M. arginini effects in vitro, we established the protein nature of the growth-supporting activity and proceeded further on to isolate and identify the responsible proteins. The use of lipid- and lipoglycan-free extracts has allowed us to further extend our studies on the biological activities of the proteins from M. arginini and to compare these results with the effects obtained using live organisms. Furthermore, the study was extended to include a characterization of the in vivo-induced effects of live M. arginini. Altogether, the results from these experiments allow us to conclude that M. arginini is a T-cell independent polyclonal B-cell mitogen, mediated by five identified proteins, inducing growth and Ig secretion of both resting and preactivated B cells.