Immunoglobulins of the Human Amniotic Fluid

Quan CP, Forestier F, Bouvet J‐P. Immunoglobulins of the human amniotic fluid. AJRI 1999; 42:219–225 © Munksgaard, Copenhagen PROBLEM: Except for the description of a secretory immunoglobulin (S‐Ig) of a low size, no recent study has investigated the molecular status of antibodies in the human amniotic fluid. METHOD: After separation with a high performance chromatography, we analyzed 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 detected. IgA is monomeric, with a low level of secretory IgA and with various amounts of free secretory component (SC). The presence of a low level of SC‐containing immunoglobulin of a low size is confirmed during the last trimester of pregnancy. This molecule contains no α chain but includes a Fabγ fragment noncovalently associated with SC. IgG, IgA, and SC are detected 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 autoantibodies is discussed.