Characterization of N-terminal amino acid sequence of monoclonal nonspecific suppressor factor

Production and characterization of a monoclonal antibody specific for ubiquitin-like polypeptide responsible for nonspecific immune suppression

Monoclonal nonspecific suppressor factor (MNSF) is a lymphokine product of a murine T cell hybridoma that inhibits the immune response in an antigen nonspecific manner. Recently, we found that a novel ubiquitin-like protein (Ubi-L), a subunit of MNSF, is responsible for its biological activity. We developed a monoclonal antibody with specific activity against Ubi-L. Inhibition experiments showed that this mAb, termed NA4, preferentially recognizes Ubi-L but not irrelevant proteins such as ubiquitin. With the use of NA4, we established an ELISA method for the quantitation of Ubi-L. By this ELISA system, approximately 40 ng/ml of MNSF was detected in the culture supernatants of concanavalin A (Con A)- or interferon gamma (IFN gamma)-activated splenocytes, whereas MNSF in the supernatant of IFN alpha- and IFN beta-stimulated splenocytes was nil. In addition, NA4 could abrogate the action of Ubi-L. Thus NA4 was confirmed to be a pertinent tool for elucidation of the underlying mechanism of action of MNSF.

Homology of partial primary sequences between alpha-enolase and a suppressive lymphokine from human T cells

A relationship is described between TS--a human suppressive lymphokine produced by hybridoma T cells--and alpha-enolase from the U937 monocyte human cell line. A strong homology (92%) was observed by comparing the internal amino acid sequences of 6 TS peptides, corresponding to 52 residues, with the complete sequence of alpha-enolase. The molecular masses of these two molecules were found to be of about 47 kDa and both were detected with the same monoclonal antibody to TS. In contrast, no immunosuppressive activity was detected with the purified enolase fraction, whereas TS did not show any enolase activity. A suppressive monokine secreted by U937 cells was found to be unrelated with TS. Theses results suggest that the TS immunosuppressive factor despite its absence of enzyme activity, belongs to the enolase family.

Monoclonal nonspecific suppressor factor beta (MNSF beta) inhibits the production of TNF-alpha by lipopolysaccharide-activated macrophages

The monoclonal nonspecific suppressor factor (MNSF), a lymphokine produced by a murine T cell hybridoma, shows a pleiotropic antigen-nonspecific suppressive function. Most recently, a cDNA encoding a subunit of MNSF (MNSF beta) has been isolated and characterized. Recombinant form of MNSF beta (rMNSF beta) inhibits lymphokine functions, as does native MNSF. In this study, we investigated whether rMNSF beta also affects macrophage function in terms of LPS-induced TNF-alpha production by a mouse macrophage cell line, J774. rMNSF beta suppressed the TNF-alpha production in a dose-dependent manner. This suppressive effect was remarkably reduced when rMNSF beta was added after 6 h of LPS stimulation. In addition, enhancement of TNF-alpha production by IFN-gamma was also suppressed by rMNSF beta. The suppressive effect was partly neutralized by the addition of the serine/threonine phosphatase inhibitor, okadaic acid. This finding suggests that serine/threonine protein phosphatases type 1 and/or 2A may be implicated in the mechanism of action of MNSF.

Molecular cloning and characterization of a cDNA encoding monoclonal nonspecific suppressor factor

The monoclonal nonspecific suppressor factor (MNSF) is a lymphokine product of a murine T-cell hybridoma that inhibits the generation of lipopolysaccharide-induced immunoglobulin-secreting cells in an antigen-nonspecific manner. A cDNA clone encoding MNSF beta (an isoform of MNSF) was isolated and expressed in bacteria. The sequence obtained is virtually identical to the Fau protein, a product of the ubiquitously expressed fau gene with unknown function. Northern blot analysis demonstrated a single, 0.6-kb transcript. Specific polyclonal antibodies against synthetic peptides corresponding to the deduced amino acid sequences were elicited in rabbits. Immunoprecipitation experiments with these antibodies showed that MNSF beta is released extracellularly in an aggregate form, albeit it lacks a signal peptide sequence. The anti-MNSF beta affinity eluate from the MNSF-producing murine hybridoma (E17) and concanavalin A-activated splenocyte culture supernatants inhibited the immunoglobulin production by lipopolysaccharide-activated splenocytes. Recombinant MNSF beta also showed a similar biologic activity. Thus, ubiquitin-like protein(s) may be involved in the regulation of the immune responses.

Human nonspecific suppressor factor (hNSF): cell source and effects on T and B lymphocytes

The human nonspecific suppressor factor (hNSF), the probable counterpart of the murine monoclonal nonspecific suppressor factor (MNSF), has been isolated from the ascitic fluid of a patient with systemic lupus erythematosus and characterized. hNSF presents an inhibitory activity on the proliferation and IgG production of mitogen stimulated human PBMC. In the present study, we demonstrate that hNSF can be isolated from the supernatants of ConA-activated T cells, but not from CD8-depleted T cells, indicating the CD8+ T cells are the major source of the factor. We also studied the effects of hNSF on purified human B and T cells; hNSF strongly inhibited the proliferation and Ig secretion by highly purified B cells induced by SAC plus IL-2, as well as the proliferation of T cells activated by Con A plus IL-2. These results indicate that hNSF is a CD8+ T cell product with strong antigen-nonspecific immunoregulatory action on both lymphocyte populations.

Monoclonal non-specific suppressor factor (MNSF) inhibits the IL4 secretion by bone marrow-derived mast cell (BMMC)

We investigated whether monoclonal non-specific suppressor factor (MNSF) has an effect on the IL4 secretion by BMMC sensitized with anti-DNP IgE monoclonal antibody. The sensitized BMMC showed a maximum increase of IL4 secretion at 10 ng/ml antigen activation. When MNSF (10 U) was added, it remarkably suppressed the IL4 secretion (82 +/- 3%). MNSF also suppressed the IL4 secretion by the mast cell line, CFTL-15, but not CFTL-12. Northern blot analysis showed that, when the same amounts of MNSF were added, IL4 mRNA expression was decreased, suggesting that the suppression results from the inhibition of a transcript.

IFN-gamma enhances the expression of cell surface receptors for monoclonal nonspecific suppressor factor

Monoclonal nonspecific suppressor factor (MNSF) is a lymphokine derived from a murine T cell hybridoma. The action of MNSF is mediated by specific cell-surface receptors. Since IFN-gamma alters the cellular response to MNSF (M. Nakamura, H. Ogawa, and T. Tsunematsu, J. Immunol. 138, 1799, 1987), we investigated whether IFN-gamma has an effect on the expression of MNSF receptor on target cells. IFN-gamma enhanced the expression of MNSF receptor on both MOPC-31C cells (a murine plasmacytoma line) and EL4 (a murine T lymphoma line). Incubation with IFN-gamma increased the number of specific MNSF-binding sites by about 50 to 90%, with no significant change in binding affinity. IFN-alpha and IFN-beta also increased MNSF binding, although the effect of the saturating amounts was lower than that seen with IFN-gamma. Maximal enhancement of receptor expression was observed after about 15 hr of incubation with IFN-gamma. No demonstrable change occurred in the kinetics of internalization of 125I-MNSF bound to MOPC-31C cells preincubated without or with IFN-gamma.