American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the primary immunoglobulin involved in the linear deposition along the glomerular basement membrane in anti-GBM antibody disease?

1. IgA

2. IgM

3. IgD

4. IgG

The correct answer is: IgG

The primary immunoglobulin involved in the linear deposition along the glomerular basement membrane in anti-GBM (glomerular basement membrane) antibody disease is IgG. This condition, also known as Goodpasture syndrome when associated with pulmonary hemorrhage, is characterized by the presence of circulating antibodies that specifically target the collagen type IV in the glomerular basement membrane. In this disease, IgG antibodies bind to the glomerular basement membrane, leading to the activation of the complement system, inflammatory cell recruitment, and subsequent glomerular injury. The linear staining pattern observed on immunofluorescence microscopy is indicative of this deposition of IgG antibodies. As the predominant antibody type in this pathology, IgG plays a crucial role in the mechanisms of damage to the kidney. While other immunoglobulin types like IgA, IgM, and IgD have distinct roles in the immune response, they are not primarily responsible for the pathogenesis of anti-GBM disease. This specificity of IgG in targeting the glomerular basement membrane is fundamental to understanding the disease's mechanism and its clinical manifestations.