Purification and partial sequence of human osteoclast-activating factor: identity with interleukin 1 beta

Area of Science:

• Immunology
• Endocrinology
• Molecular Biology

Background:

• Osteoclast-activating factor (OAF) is a lymphokine involved in bone resorption.
• The precise identity and source of OAF have been under investigation.

Purpose of the Study:

• To purify osteoclast-activating factor (OAF) to homogeneity.
• To determine the molecular identity of OAF.
• To characterize the biological activity of purified OAF.

Main Methods:

• Purification of OAF from human peripheral blood mononuclear cells using gel filtration, ion-exchange, and reverse-phase HPLC.
• Assessment of homogeneity via SDS-PAGE, isoelectric focusing, and amino-terminal sequencing.
• Measurement of bone resorptive activity by calcium release from fetal rat long bones.
• Assay of thymocyte proliferation activity.

Main Results:

• OAF was purified to homogeneity, exhibiting a single band on SDS-PAGE (17.8 kDa) and isoelectric focusing (pI 6.8).
• Purified OAF demonstrated potent bone resorptive activity (EC50 ~0.66 ng/ml) and thymocyte proliferation activity (8.2 x 10^6 U/mg).
• The amino-terminal sequence of OAF was identical to that of interleukin 1 beta.

Conclusions:

• Osteoclast-activating factor (OAF) and interleukin 1 beta (IL-1β) are the same molecule.
• Interleukin 1 beta is the major protein responsible for OAF activity in lectin-stimulated peripheral blood mononuclear cells.
• This identification clarifies the role of IL-1β in bone metabolism and immune responses.