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Identification of a unique T cell-derived lymphokine that primes macrophages for tumor cytotoxicity
D E Kern1, K H Grabstein, K Okuno
1Department of Microbiology/Immunology, University of Washington, Seattle 98195.
Abstract:
Macrophage activation factor (MAF) activity, assessed by the ability to activate macrophages (MO) to lyse RBL--a TNF-resistant, retrovirally transformed, tumor target--was detected in the PHA-stimulated supernatant (Sup) of LBRM, a murine T cell line. LBRM Sup provided a priming signal to MO, but required the subsequent addition of small amounts of LPS for the expression of tumor cytotoxicity. The identity of the lymphokine responsible for this MAF activity was investigated. IFN-gamma, the only previously characterized lymphokine capable of priming MO for tumor cytotoxicity, did have MAF activity in the assay, but IFN-gamma could not be detected by ELISA in LBRM Sup, and LBRM-derived mRNA lacked detectable message for IFN-gamma. Moreover, anti-IFN-gamma failed to inhibit the MAF activity of LBRM Sup, suggesting that the presence of small, undetectable amounts of IFN-gamma were neither responsible nor required for LBRM MAF activity. LBRM MAF activity appeared distinct from the other previously identified lymphokines produced by LBRM, since granulocyte-macrophage-CSF, IL-2, and IL-3 purified from LBRM Sup were unable to activate MO to lyse RBL. IL-4 and TNF, two lymphokines not known to be produced by LBRM but able to activate MO for cytotoxicity of some tumor targets, were also unable to activate MO for RBL cytotoxicity. LBRM MAF lacked antiviral activity in biologic assays, further distinguishing the lymphokine from IFN-gamma, and had an apparent Mr of 30,000 Da using gel filtration chromatography. Thus, the LBRM T cell line produces a previously undescribed lymphokine that primes MO for tumor cytotoxicity.
Insights
Researchers identified a novel lymphokine from a murine T cell line that activates macrophages to lyse tumor cells. This macrophage activation factor (MAF) is distinct from known cytokines like IFN-gamma.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Macrophage activation is crucial for tumor cytotoxicity.
- Identifying novel factors that mediate macrophage activation is essential for understanding immune responses.
- Previous studies identified IFN-gamma as a key lymphokine for macrophage priming.
Purpose of the Study:
- To identify the lymphokine responsible for macrophage activation factor (MAF) activity in LBRM supernatant.
- To characterize the properties of this novel MAF.
- To differentiate it from known lymphokines like IFN-gamma.
Main Methods:
- Assessing MAF activity by macrophage (MO) lysis of RBL tumor targets.
- Stimulating LBRM T cell supernatant with PHA.
- Using ELISA and mRNA detection to identify IFN-gamma.
- Testing other lymphokines (GM-CSF, IL-2, IL-3, IL-4, TNF) for MAF activity.
- Gel filtration chromatography to determine molecular weight.
Main Results:
- LBRM supernatant exhibited MAF activity, priming MO for tumor cell lysis.
- IFN-gamma was not detected in LBRM supernatant and anti-IFN-gamma did not inhibit MAF activity.
- Other tested lymphokines (GM-CSF, IL-2, IL-3, IL-4, TNF) did not mediate RBL cytotoxicity.
- The novel MAF lacked antiviral activity and had an apparent molecular weight of 30,000 Da.
Conclusions:
- The LBRM T cell line produces a novel lymphokine with MAF activity.
- This lymphokine is distinct from IFN-gamma and other known cytokines.
- This discovery opens new avenues for understanding macrophage-mediated tumor cytotoxicity.