Immunoglobulin A (IgA) is an antibody that helps keep our gut and mucus linings healthy. IgA exists as two isotypes: IgA1 and IgA2. IgA1 normally hangs out in serum, whereas IgA2 is mostly in secretions. This model showcases IgA2 as a monomer, though it can exist in a dimeric form called secretory IgA (sIgA). This is a surface representation, based on backbone atoms only.