Mycoplasma neurolyticum: a potent mitogen for rat B lymphocytes

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.

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.

Thymosin and the spontaneously diabetic BB rat

The biological basis for autoimmunity and immunoincompetence in the BB rat has yet to be localized. In spite of normal thymic histology, thymocyte subsets and blastogenesis, thymus gland products (thymosins) have yet to be studied. In the present report, thymus gland function was studied by measuring thymosin alpha 1 levels at one time point in the BB rat compared with control rates, and BB rat responses to exogenous thymosin (Thymosin fraction 5) were observed. At five months of age, BB rats had thymosin alpha 1 levels comparable to Lewis and Wistar furth rats. Thymosin fraction 5 increased the ratio of peripheral blood W3/25 positive to OX8 positive cells, but otherwise had no effect on the BB rats' T-cell immunodeficiency, or frequencies of tissue autoantibodies or insulin-dependent diabetes. Although B-lymphocyte counts were normal in BB rats, splenocyte responses to B-lymphocyte mitogens were depressed. However, thymosin fraction 5 improved the BB rat B-lymphocyte blastogenesis to near normal for Mycoplasma neurolyticum. Coupled with our previous work, our results suggest that the immune derangement in the BB rat resides outside the thymus.

Biochemical characterization of the T-cell mitogen derived from Mycoplasma arthritidis

A biochemical procedure is described to purify the T-cell mitogen in the supernatant of cultured Mycoplasma arthritidis organisms. The mitogenic material was bound on an affigel blue column. The eluate of this column was then acylated at 0 degrees C for 1.5 h and subsequently chromatography on a Sepharose Cl 6B and a Superose 12HR column were performed. SDS-PAGE showed a major band at MW 26,000 and some minor bands at 50,000. With this material biological tests were performed, including induction of lymphoproliferation and interferon induction in murine spleen cell cultures. Purified Mycoplasma arthritidis supernatant (MAS) vigorously stimulated spleen cell cultures of A/J, CBA, C3H/He, and DBA/2 mice, whereas a low-grade but definitive response was observed in C57BL/6 spleen cells. Cultures of Balb/c nu/nu mice, in contrast to those of their euthymic littermates, were non-reactive. When induction of interferon was tested, a marked response to purified MAS was observed in CBA and C3H/HeJ spleen cell cultures, whereas C57BL/6 spleen cells were non-reactive.

Mycoplasma neurolyticum membranes: a T-independent antigen in the rat

Our understanding of the mechanisms involved in B cell activation, proliferation and differentiation to immunoglobulin secreting cells has been facilitated by the use of T-independent and T-dependent antigens. The majority of these studies have used the murine system and only recently, the rat. Because membranes isolated from Mycoplasma neurolyticum are potent B cell mitogens in the rat and some T-independent antigens also activate DNA synthesis in B cells, the in vitro and in vivo antibody responses induced by M. neurolyticum membranes in T-deficient rat systems were examined. The three groups of rats used, i.e., nude; anti-thymocyte serum-treated, neonatally-thymectomized (ATS-Tx); and normal Fischer 344 produced a non-polyclonal antibody response against the membranes. Spleen cell cultures that were T cell deficient and B cell enriched produced plaque-forming cells against the Mycoplasma membranes. Antibody production was depleted upon removal of Sephadex G-10 adherent cells. The antibody response is comprised of both antigen-specific and polyclonal responses. Lipoglycan, found in the aqueous phenol extract of the membranes, is the mitogenic fraction of the membranes, and this study suggests that it may also be the T-independent antigenic component of the M. neurolyticum membranes.

Stimulation of lymphoid cell proliferation by Mycoplasma orale, a common cell culture contaminant

Mycoplasma orale, maintained as a contaminant of a mouse hybrid cell line, induces an intense proliferation in short-term culture of lymphoid cells of inbred mice. Cell division induced by the contaminated cell culture fluid reaches a maximum on day four and declines rapidly thereafter. Culture fluids from hybrid cells freed of contamination do not cause proliferation. Cells from the spleen, bone marrow, and thymus of each of several strains of inbred mice, including xid CBA/N, poorly responsive to lipopolysaccharide, are stimulated by the mitogen, as are cells from BALB/c nude mice. The characteristics of the stimulatory effect are analogous in several important aspects to those of naturally occurring T cell-derived growth factors. In the absence of detectable numbers of T cells, both small and large B lymphocytes undergo mitosis in the presence of contaminated cell culture fluid, and B cells stimulated to divide by lipopolysaccharide are sustained for further rounds of replication by M. orale-containing cell culture fluid. The fluid also augments the stimulatory effect on thymocytes of suboptimum concentrations of phytohemagglutinin mimicking the effect of interleukin-1. Unlike with most naturally occurring lymphoid cell mitogens, however, the dividing cells do not go on to immunoglobulin secretion.

Differentiation in the murine B cell lymphoma I.29: inductive capacities of lipopolysaccharide and Mycoplasma fermentans products

Cells from the murine B lymphoma I.29, expressing IgM or IgA of identical idiotype, were found inducible by lipopolysaccharide to differentiate into plasma cells. Within 3 days, differentiating cells lost membrane-bound immunoglobulin (Ig) and accumulated large quantities of intracytoplasmic Ig. At day 6 of culture, IgA secretion increased 50-100-fold, as determined by enzyme-linked immunoassay. Proliferation increased for the first days of culture but decreased thereafter; by day 10 very few viable cells were present in lipopolysaccharide-stimulated cultures. Similar results were obtained by culturing I.29 cells in the presence of supernatants of certain B cell lines (e.g. BFO.3). The finding of a strict correlation between the inductive activity and presence of contaminating Mycoplasma fermentans suggested that factor(s) released by mycoplasma were responsible for the mitogenic activities. This was further indicated by the findings that: the supernatants of BFO.3 that were rendered free of mycoplasma were not inductive, and a nonactive cell line could be made active by infection with supernatants of BFO.3 cells containing viable microorganisms. Thus, supernatants of mycoplasma-infected cell lines may act as potent polyclonal activators on both normal and malignant B lymphocytes. The ability to induce membrane Ig on 70Z/3 cells indicates that mycoplasma-related mitogens are also active on pre-B cells. The possibility of mycoplasma contamination should thus be carefully excluded when presumptive factors of cloned cell lines are being evaluated.

Lymphoproliferation induced in mouse spleen cells by Mycoplasma arthritidis mitogen. Reversal of the defect of nonresponder mice

Spleen cells of various mouse strains (e.g. BALB/c, C311, and CBA) reacted towards MAS (a mitogen derived from supernatants of cultured Mycoplasma arthritidis) with a marked lymphoproliferative response. This reactivity was T-cell-dependent. It was reduced by 90% after removal of macrophages by passage of the spleen cells through Sephadex G-10 columns. Addition of 2-mercaptoethanol (2-ME) to macrophage-depleted CBA spleen cells completely restored the response to MAS. Spleen cells of C57BL/6 and C57BL/10 mice were unreactive to MAS, even in the presence of macrophages, and this non-reactivity was controlled by the I-region of H-2. Other mouse strains that, similarly to C57BL/6, lack the expression of I-E on the cell surface (that is, mice of the haplotype H-2f, H-2q, and H-2s) were also non-responsive to MAS. However, the addition of 2-ME to spleen cells of non-responder mice resulted in high lymphoproliferative responses to MAS, which were as high as those of CBA spleen cells. The reaction of C57BL/6 spleen cells to MAS in the presence of 2-ME again was T-cell-dependent, as shown by data with spleen cells of homozygous nude mice and spleen cells treated by anti-thy-1 and C. A macrophage dependency of this response was also evident. When C57BL/6 spleen cells were vigorously freed of accessory cells by the use of nylon wool columns, the MAS response could no longer be restored by 2-ME.

Role of mitogenicity in pathogenicity of mycoplasmas for murine hosts

The mitogenicity and pathogenicity of Mycoplasma pulmonis were compared in two rat strains. Both the mitogenic and the pathologic effects induced by M. pulmonis membranes were more severe in Lewis rats than in Hooded rats, and were dependent on the mitogen doses used. It was concluded that the severity of lung lesions induced by M. pulmonis membranes correlated with the degree of mitogenic responses of the different rat strains to this organism. The roles of T- and B-cell mitogens in induction of pneumonia were studied in Hooded rats treated intranasally with either the T-cell mitogen concanavalin A or with M. neurolyticum membranes which stimulate the B-cell populations, or with both concanavalin A and M. neurolyticum. Results clearly showed that the individual B- and T-cell mitogens affected the lungs of treated animals. Nevertheless, the mitogenic co-stimulation of both B and T lymphocytes in rat lungs was necessary to obtain maximal development of interstitial lymphocytic pneumonia.

Age-related changes in responsiveness of various rat tissue lymphocytes to mitogens

The effect of age on the mitogen responses of rat lymphoid tissues was investigated. Evaluation was based on using the in vitro proliferative response of lymphocytes from various tissues of Fischer-344 rats (2, 7, 13, 19 and 25 months) using concanavalin A (Con A), phytohemagglutinin-P (PHA-P), pokeweed mitogen (PWM) and Mycoplasma neurolyticum. The stimulation index (S.I.) for cervical, mesenteric, thymic and splenic lymphocytes treated with Con A and PHA-P was greatest for 2-month-old rats and lowest for 19-month-old rats; however, no age-related change was observed with either PWM or M. neurolyticum. The levels of mitogenic responses for lymph nodes in the two different anatomical sites paralleled one another, with the cervical lymphocytes showing a greater response. The splenic lymphocytes responded less than either lymph node lymphocyte population. When PHA-P treatment of splenic lymphocytes followed the removal of the plastic adherent population, the S. I. of the resulting non-adherent population was comparable to the S. I. of other tissue lymphocytes; however, an age-related decrease was still observed. The PHA-P proliferative response of either the 7- or 19-month non-adherent population was suppressed by the 7-month adherent population and not by the 19-month adherent population i.e., adherent population interaction with non-adherent population decreases with age.