Characterization of a human monocyte cytotoxicity-inducing factor (MCF)

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Monocyte cytotoxicity-inducing factor (MCF) was previously identified as a lymphokine distinct from interferon-gamma (IFN-γ).
• Further characterization is needed to understand MCF's properties and biological functions.

Purpose of the Study:

• To characterize the biochemical properties of MCF.
• To investigate the effects of MCF on monocyte activation and function.
• To differentiate MCF from other known cytokines.

Main Methods:

• Biochemical assays were used to determine MCF's sensitivity to proteases (chymotrypsin, trypsin) and nucleases (RNase, DNase).
• Protein synthesis inhibitors (actinomycin D, puromycin, cycloheximide) were used to study MCF production.
• Isoelectric focusing and gel electrophoresis were employed to determine MCF's charge heterogeneity and molecular weight.
• Monocyte activation assays were performed to assess MCF's ability to induce cytotoxicity and cytokine secretion (IL-1, TNF).

Main Results:

• MCF was inactivated by chymotrypsin but not by trypsin, RNase, or DNase, suggesting a protein nature.
• MCF production was dependent on active protein synthesis, as indicated by inhibition with actinomycin D, puromycin, and cycloheximide.
• Native MCF exhibited charge heterogeneity with isoelectric points at 2.7, 5.6, and 6.7, and molecular weights of 29 kDa and 14.7 kDa.
• MCF-activated monocytes effectively lysed both NK-sensitive and NK-resistant tumor targets.
• MCF-activated monocytes secreted IL-1 but not TNF.

Conclusions:

• MCF is a distinct lymphokine with unique biochemical properties.
• MCF activates monocytes to lyse tumor targets.
• MCF is different from TNF, IL-1, IL-2, IFNs, and CSFs.