[IgA, an essential part of the immune system: selected issues].

Immunoglobulin class A is the main protein of the mucosal immune system. The daily production of this isotype exceeds the synthesis of all other classes of immunoglobulins. Because the mucosal surface area of the human organism is about 400 m2, the role of IgA in the defense of this surfaces from harmful agents from the external environment is extremely essential. Any changes connected with a lack or an overproduction of this immunoglobulin can manifest as different clinical diseases. In this paper some selected issues on the heterogeneity of the IgA are presented, its structure and significance for the human organism, the formation of IgA immunity during ontogenesis on one hand and antigenic stimulation on the other, as well as disorders connected with abnormal synthesis or structure of these molecules.