Purification of bullous pemphigoid IgG subclasses and their capability for complement fixation

Area of Science:

• Immunology
• Dermatology
• Biochemistry

Background:

• Bullous pemphigoid (BP) is an autoimmune blistering disease characterized by autoantibodies against hemidesmosomal proteins.
• The role of specific immunoglobulin G (IgG) subclasses in BP pathogenesis and complement activation remains incompletely understood.

Purpose of the Study:

• To investigate the reactivity and complement-fixing capability of circulating IgG subclasses in patients with bullous pemphigoid.
• To determine which IgG subclasses are present in BP sera and their ability to deposit in skin and fix complement.

Main Methods:

• Purification of polyclonal IgG subclasses (IgG1, IgG2, IgG3, IgG4) from BP patient sera using a combination of chromatography techniques including DEAE Affi-Gel Blue, protein A-Cellulofine, and IgG subclass-specific immuno-affinity chromatography.
• Immunohistopathological techniques were employed to detect IgG and C3 deposits in normal human skin incubated with purified IgG subclasses.

Main Results:

• IgG deposits were detected at the basement membrane zone (BMZ) in normal skin incubated with IgG1, IgG2, and IgG4 subclasses, but not with IgG3.
• Complement component C3 deposits were observed at the BMZ exclusively when the skin was incubated with the IgG1 subclass.
• No IgG or C3 deposits were found in skin incubated with the IgG3 subclass.

Conclusions:

• The circulating IgG subclass antibodies in bullous pemphigoid patients include IgG1, IgG2, and IgG4, but notably exclude IgG3.
• The IgG1 subclass is the primary driver of complement fixation in bullous pemphigoid, suggesting a significant role in disease pathogenesis.