IgA (Immunoglobulin A) is one of the classes of antibodies produced by the immune system. When someone has antiphospholipid antibodies of the IgA class, it means that these specific antibodies are of the IgA isotype. IgA antibodies are typically associated with mucosal immunity, but in the context of APS, they can contribute to the formation of blood clots and other complications associated with the condition.