Immunoglobulins of the human amniotic fluid

PROBLEM: Except for the description of a secretory immunoglobulin (S-Ig) of a low size, no recent study has investigated the molecular status of antib odies in the human amniotic fluid. METHOD: After separation with a high performance chromatography, we analyze d the different isotypes of amniotic Igs by immunoblotting and ELISA. RESULTS: IgG is found to be the major isotype and to contain mother-derived tetanus antitoxins. IgA is much less abundant, whereas no IgM can be detec ted. IgA is monomeric, with a low level of secretory IgA and with various a mounts of free secretory component (SC). The presence of a low level of SC- containing immunoglobulin of a low size is confirmed during the last trimes ter of pregnancy. This molecule contains no alpha chain but includes a Fab gamma fragment noncovalently associated with SC. IgG, IgA, and SC are detec ted in the fetal urine and, therefore, can reach the amniotic fluid by this route. CONLUSION: In addition to the predominant maternal IgG, the amniotic fluid contains different molecular forms of fetal immunoglobulins. Their function as an immune barrier against infection and against mother-derived autoanti bodies is discussed.