Circulating IgG-LD complex, dissociable by addition of NAD+

Area of Science:

• Biochemistry
• Immunology
• Pulmonology

Background:

• Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease with complex pathophysiology.
• Autoimmune conditions can present with various autoantibodies and immune complexes.
• Lactate dehydrogenase (LD) is a key enzyme in cellular metabolism, often measured as a biomarker.

Observation:

• Macromolecular lactate dehydrogenase (LD) was detected in the serum of a patient with idiopathic lung fibrosis and autoimmune disease symptoms.
• Gel filtration and affinity chromatography revealed that most serum LD activity existed as LD-IgG complexes.
• These complexes dissociated upon the addition of nicotinamide adenine dinucleotide (NAD+).

Findings:

• The formation of LD-IgG complexes was not due to a deficiency of circulating NAD+.
• The data strongly suggest the presence of LD-binding sites on IgG molecules in this patient.
• NAD+ appears to disrupt the LD-IgG complex, possibly by competing for the LD active site or inducing conformational changes.

Implications:

• This finding may offer new insights into the pathogenesis of lung fibrosis associated with autoimmune diseases.
• Understanding LD-IgG complex formation could lead to novel diagnostic or therapeutic strategies.
• The role of enzyme-antibody complexes in disease requires further investigation.