Neutrophil elastase-cleaved corticosteroid-binding globulin is absent in human plasma

Area of Science:

• Biochemistry
• Immunology
• Endocrinology

Background:

• Corticosteroid-binding globulin (CBG) is crucial for glucocorticoid transport.
• Neutrophil elastase (NE) cleavage of CBG's reactive center loop (RCL) impairs steroid binding.
• ELISAs using specific monoclonal antibodies have suggested the presence of circulating RCL-cleaved CBG.

Purpose of the Study:

• To investigate the biochemical properties of plasma CBG.
• To identify the presence of RCL-cleaved CBG in human blood samples.
• To reconcile discrepancies observed in CBG ELISAs.

Main Methods:

• Analysis of plasma CBG-binding capacity and ELISA values from various blood sources.
• Heat-dependent polymerization assay to detect cleaved CBG.
• Immunoprecipitation assays using specific monoclonal antibodies.
• Mass spectrometry to confirm NE-cleaved CBG absence.

Main Results:

• Plasma CBG-binding capacity and ELISA values were consistent across different blood types and tissues.
• RCL-cleaved CBG was undetectable in plasma from critically ill patients.
• No evidence of NE-cleaved CBG was found using multiple biochemical assays, including mass spectrometry.
• CBG resistant to immunoprecipitation maintained high steroid-binding affinity.

Conclusions:

• Circulating human CBG with a NE-cleaved RCL and low steroid affinity is absent in blood samples.
• Discrepancies in CBG ELISAs likely result from structural variations affecting antibody epitopes, not the presence of cleaved CBG.
• Current immunoassays may misinterpret structural differences as evidence of cleaved CBG.