Humoral immunity

The circulating antibodies, which are also termed immunoglobulins - abbreviated as Ig - with various classes (Ig A, D, E, G and M, with diverse subclasses), are responsible for humoral immunity. They are produced exclusively by B-lymphocytes. Antibodies constantly and efficaciously defend our bodies in that they inactivate viruses or bacterial toxins and launch the complement-system (see below) or set the various types of white blood cells at phagocytosing microorganisms and even larger parasites. Their absolutely unique characteristic is that they have abundant various forms, of which each possesses a different amino acid sequence and a completely individual binding site for antigens. Immunoglobulins are one of the main blood components, making up roughly 30% of all plasma proteins.