Antibodies against acute phase proteins and their functions in the pathogenesis of disease: a collective profile of 25 different antibodies.

The acute phase response is a defense system in which the innate immune response is activated following injury or infection. Positive and negative acute phase proteins (APPs) are crucial for protecting the host organism, as well as returning it to homeostatic levels, the first with elevated concentrations and the latter with decreased concentrations during the acute phase. Reports about the presence of antibodies against APPs are known, however their individual, as well as potentially collective, pathological or physiological roles are still emerging. Some of these autoantibodies are specifically connected with diseases (such as pancreatic secretory trypsin inhibitor and C3, C4 nephritic factors), while others have been reported as natural antibodies. The persistent presence (even if only minor) of autoantibodies in healthy blood donors indicates an overlapping category of autoantibodies, which could become pathogenic, depending on the autoantibody characteristics such as avidity, epitope specificity, changes in the microenvironment leading to different oxidative status and others. This review uses the novel approach of studying the overall autoantibody population against APPs, their functions and connections to diseases. The primary function of autoantibodies against APPs (anti-APPs) is thought to promote their clearance, however autoantibodies against negative APPs have also been found and applying the same role to those is doubtful. There is also the theory of consumption in the stage of inflammation, which could be relevant to anti-APPs. Reports about protective roles of autoantibodies are also emerging, showing lowered levels of antibodies in diseases, which could be interesting for therapeutic intervention.