[Immunologic relevance of malonic dialdehyde].

Free radicals are involved in many physiological and pathological processes, including oxidation of polyunsaturated fatty acids, i.e. lipoperoxidation. Among the different by-products of this lipoperoxidation, malonic dialdehyde (MDA) has been one of the most studied. It reacts with the primary amino groups of biological molecules, especially those of proteins, with formation of 1-amino-3-imino-propene (AIP) bridges. Studies undertaken in our laboratory about the immunological relevance of MDA have first shown the existence of antibodies (AcAIP) recognizing epitopes containing AIP bridges, and reacting specifically with MDA-modified proteins but not with the corresponding native ones. These antibodies occur even under physiological conditions, independently of any disease or any stimulation induced by antigen injection. However, their seric level may be modified in pathologies involving an increased lipoperoxidation and/or an inflammatory process (cardiovascular pathology, diabetes, alcoholism). Injections of a MDA-protein adduct to rabbits or mice stimulates AcAIP production, even if the protein contained in the adduct in an autologous one, but such injections may also result in production of other antibodies. Other results obtained in our laboratory indicate that AcAIP are involved in elimination of senescent or lipoperidized erythrocytes, and probably also in discarding other cells having undergone oxidative stress, at least the circulating ones. The physiological and pathological implications of MDA and AcAIP have lead us to formulate hypotheses about their more general role within the immune system, and to try to situate them in this system. Of course, these hypotheses remain to be assessed by further experimentations.