Relationship among IgE-binding factors with various molecular weights.

Area of Science:

• Immunology
• Molecular Biology

Background:

• Rat-mouse T cell hybridoma 23B6 produces IgE-binding factors (IBFs) upon stimulation with IgE.
• These IBFs exist in various molecular weight forms (60K, 30K, 14K, 10K) both intracellularly and extracellularly.

Purpose of the Study:

• To investigate the structure, function, and origin of IgE-binding factors produced by T cell hybridoma 23B6.
• To determine which molecular weight forms of IBFs are responsible for suppressing IgE responses.

Main Methods:

• Incubation of hybridoma cells with IgE.
• Analysis of intracellular and secreted IBFs by molecular weight.
• Functional assays to assess IgE response suppression.
• Biochemical modification (reduction and alkylation) of IBFs.
• Transfection of COS 7 cells with a cloned cDNA (8.3) encoding rodent IBF.

Main Results:

• Extracellular 60K and 14K IBFs suppressed IgE responses, while 30K and 10K IBFs did not.
• Reduction and alkylation of 60K IBFs yielded 30K, 14K, and 10K fragments; only 14K fragments suppressed IgE responses.
• A 60K IBF precursor molecule was identified, with smaller forms derived through post-translational modification.
• Transfection studies revealed 60K and 11K IBFs with potentiating activity, suggesting different functional roles for different forms.

Conclusions:

• The 60K IgE-binding factor is a precursor molecule.
• Post-translational modification generates smaller IBFs (30K, 14K, 10K) with distinct functional properties.
• The 14K IBF is crucial for suppressing IgE responses.