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A human 15-kDa IFN-induced protein induces the secretion of IFN-gamma
M Recht1, E C Borden, E Knight
1University of Wisconsin Clinical Cancer Center, Madison.
Abstract:
A 15,000 molecular weight protein (15-kDa), induced and secreted by human PBMC after treatment with IFN-alpha or -beta, was assessed for its ability to modulate cellular function. Although it had no effect on growth or 2'5'-A synthetase activity in Daudi, U-937, or HL-60 cells, when incubated with fresh human PBMC, LPS-induced monocyte cytotoxicity against WEHI-164 target cells was augmented. This stimulation was inhibited by both an antibody against TNF-alpha and a rabbit polyclonal antiserum to the 15-kDa protein. Furthermore, when the 15-kDa protein was added to PBMC an increase in GTP cyclohydrolase I activity, as assessed by neopterin secretion, resulted. Neopterin secretion by PBMC in response to the 15-kDa was increased in a dose-responsive manner up to more than sixfold over baseline, with a 15-kDa concentration of less than 10 ng/ml effective. The 15-kDa protein also stimulated indoleamine 2,3-dioxygenase (IDO) activity in fresh, human PBMC. Induction of neopterin secretion and IDO activity was inhibited by a polyclonal antiserum to 15-kDa. LPS-induced cytotoxic activity was not augmented by 15-kDa pretreatment of purified monocytes, indicating the need for the presence of a second cell population and the indirect action of the 15-kDa on the induction of monocyte activities. When PBMC or purified CD3+ cells, but not purified CD14+ cells, were incubated with the 15-kDa protein, secretion of a factor was induced that resulted in the induction of IDO activity in PMA-differentiated THP-1 cells. An antibody to IFN-gamma, but not IFN-alpha, inhibited the induction of IDO activity by this secreted factor. In addition, antiserum to the 15-kDa blocked the secretion of IFN-gamma from the CD3+ cells. Thus, a 15-kDa product of IFN-alpha- and IFN-beta-treated monocytes and lymphocytes can stimulate secretion of IFN-gamma from CD3+ cells.
Insights
A novel 15-kDa protein from human cells enhances immune responses by stimulating monocyte cytotoxicity and interferon-gamma secretion. This protein plays a key role in modulating cellular function and immune cell interactions.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Interferon-alpha (IFN-alpha) and Interferon-beta (IFN-beta) are crucial cytokines in the innate immune response.
- Human peripheral blood mononuclear cells (PBMC) treated with IFN-alpha or -beta secrete a 15-kDa protein.
Purpose of the Study:
- To investigate the functional role of the 15-kDa protein secreted by IFN-treated human PBMC.
- To determine the protein's ability to modulate cellular functions, including immune cell cytotoxicity and cytokine production.
Main Methods:
- Incubation of the 15-kDa protein with various cell lines (Daudi, U-937, HL-60) and fresh human PBMC.
- Assessment of cellular growth, 2'5'-A synthetase activity, lipopolysaccharide (LPS)-induced monocyte cytotoxicity, GTP cyclohydrolase I activity (neopterin secretion), and indoleamine 2,3-dioxygenase (IDO) activity.
- Use of antibodies against TNF-alpha and IFN-gamma, and antisera against the 15-kDa protein to block specific pathways.
- Analysis of secreted factors from PBMC and purified CD3+ or CD14+ cells upon 15-kDa protein stimulation.
Main Results:
- The 15-kDa protein augmented LPS-induced monocyte cytotoxicity against WEHI-164 cells, an effect inhibited by anti-TNF-alpha and anti-15-kDa antibodies.
- It dose-responsively increased neopterin secretion and stimulated IDO activity in human PBMC, with inhibition by anti-15-kDa antiserum.
- The protein's effect on monocyte cytotoxicity required a second cell population, indicating indirect action.
- A secreted factor from CD3+ cells stimulated by the 15-kDa protein induced IDO activity in THP-1 cells, an effect inhibited by anti-IFN-gamma antibody.
- Antiserum to the 15-kDa protein blocked IFN-gamma secretion from CD3+ cells.
Conclusions:
- The 15-kDa protein, induced by IFN-alpha/beta, modulates immune cell function by enhancing monocyte cytotoxicity and stimulating neopterin and IDO activity.
- This protein indirectly influences monocyte activity, requiring other cell populations.
- It induces IFN-gamma secretion from CD3+ T cells, highlighting its role in adaptive immunity.