What are the differences between the subclasses of immunoglobulin A (IgA)?

Basis of differentiation

Immunoglobulin A1 (IgA1)

Immunoglobulin A2 (IgA1)

Percentage of total IgA in serum

85%

15%

Hinge region 

Elongated, increasing sensitivity to bacterial proteases

Shorter, providing more resistance to proteases

Protease resistance

Broad resistance but some proteases can cleave the hinge region

Good resistance to proteolysis and many bacterial proteases

Immune response

Strong response to protein antigens; Moderate response to lipopolysaccharides and polysaccharides

Plays a crucial role in mucosal immunity, fighting polysaccharide and lipopolysaccharide antigens

Presence in body

More than 90% in serum; less prevalent in mucosal secretions

Predominates in mucosal secretions such as the gastrointestinal tract and airways

Allotypic variants

Not specified

Two variants defined serologically and molecularly - IgA2m(1) and IgA2m(2)

Disulfide bridges

Typical disulfide bridges linking light and heavy chains

• IgA2m(1) generally lacks disulfide bridges
• IgA2m(2) has typical disulfide bridges