Characterization of antibodies to antigens of the human amnion

The 6/2 (AA3) polyclonal antibody identifying a 37 kD keratinocyte protein reacts also with BM-600/nicein, the basement membrane component bound by the monoclonal antibody GB3

An unexpected finding concerning our previously reported polyclonal antibody raised against an extract from human amnion (pAb 6/2, also termed AA3), and which recognizes an epidermal keratinocyte protein, is presented in this study. Using the immunoblot technique, pAb 6/2 binds to a 37 kD intracellular protein antigen. We have subsequently found that, by radioimmunoprecipitation performed after metabolic labelling with 35S-methionine of cultured keratinocytes, pAb 6/2 recognizes the 600 kD epidermal basement membrane component (termed BM-600/nicein) which was reported to be bound by the monoclonal antibody mAb GB3. Specifically, pAb 6/2 reacts with immunoaffinity chromatography-isolated BM-600/nicein blotted onto nitrocellulose. The data suggest the existence of two immunological reactivities borne by pAb 6/2, each of them being directed against, respectively, the 37 kD (seen in immunoblots) and the 600 kD protein (seen in immunoprecipitations). The data further suggest possible independent expression of these two proteins in cell culture. In comparison with the staining pattern of normal skin, immunofluorescence was previously noted to be impaired (pAb 6/2) or absent (mAb GB3) in lethal junctional epidermolysis bullosa. Thus, we conclude that mAb GB3, rather than pAb 6/2, is a more appropriate probe for the comprehensive biochemical study of this genodermatosis.

Epidermolysis bullosa letalis: an immunogenetic disease of extraembryonic ectoderm?

A newborn male infant with epidermolysis bullosa letalis died at age 6 weeks of septicemia. He had many congenital ectodermal abnormalities and a rudimentary thymus. The spleen had no germinal centers and the lymph nodes lacked follicles. Cytotrophoblast of the amniochorion was sparse and the amniotic epithelium was distorted. Immunohistologic studies of amniotic epithelium revealed the unprecedented presence of trophoblast antigens. Before birth of the patient, the parents had a 5-year history of infertility; after death of the patient, the mother sustained a ruptured tubal pregnancy that necessitated blood transfusions and surgical removal of the tube. She subsequently became pregnant a third time and was delivered of a normal child. The wife shared four major histocompatibility (HLA) antigens with her husband. The parents' immunogenetic characteristics and the immunopathologic features and extraembryonic membranes of the child are considered in terms of maternal responses to trophoblast antigens.

Herpes gestationis factor reacts with the amniotic epithelial basement membrane

Sera from five patients with clinically and immunopathologically proven herpes gestationis were studied by complement fixing immunofluorescence and complement fixing immuno-electron microscopy using specimens of skin, amniochorion and placenta. The results demonstrated that the complement fixation antibody (herpes gestationis factor) could bind to the basement membrane zone of skin, amnion and chorion laeve but not to that of the placental syncytiotrophoblast. These data suggest that the herpes gestationis factor may be induced by the basement membrane zone antigens of extra-villous cytotrophoblasts.

Identification of a 37 kilodalton protein at the epidermal basement membrane by an antiserum to human amnion

A protein which is recognized by an antibody to human amniotic epithelial basement membrane was identified at the basal lamina of human epidermis by immunohistology. This protein was localized at the lamina lucida of human epidermal basement membrane by immunoelectron microscopy. Studies of normal human keratinocyte cultures and epidermal wound healing suggested that the protein was probably produced by keratinocytes. By immunoblotting, a basic apparent isoelectric pH (pHiapp = 7.3) protein band of 37 kD was seen. These data indicate that this 37 kD protein, clearly different from other known basement membrane components, is present in simple and stratified epithelia of ectodermal origin, and is associated with hemidesmosomes.

Normal epithelial antigens recognized by GB3 and GB5 are diminished in intraductal and lost in infiltrating human breast carcinomas

GB3 and GB5 are mouse monoclonal antibodies raised against human amnion. GB3 detects the epidermal basement membrane, and GB5 reacts with the junctional substances between the epithelial cells. These two antibodies were studied on breast tissues by indirect immunofluorescence. All (n = 8) of the normal mammary glandular basement membranes and epithelia reacted strongly with GB3 and GB5. In the intraductal carcinomas (n = 10), although nine out of ten tissues were reactive, their reactivities were greatly reduced. More strikingly, in the infiltrating carcinomas (n = 15), none of the tumor specimens were recognized by GB3 and only one out of fifteen biopsies was moderately reactive with GB5, indicating that the syntheses of the antigens of GB3 and GB5 were discontinued in the metastatic breast adenocarcinomas. These data suggest that these antigens may contribute to the interaction of the epithelium with the extracellular matrix and the intercellular binding between the epithelial cells; the loss of these antigens may facilitate the wide dissemination of tumor cells.

Monoclonal antibodies to human amnion

Mouse hybridoma cell lines secreting monoclonal antibodies to human amnion were established. The reactivities of eight of these monoclonal antibodies (GB1, GB3, GB4, GB5, GB6, GB9, GB10 and GB11) on human skin and term extra-embryonic tissues, which included reflected amniochorions, basal plates, placentae, chorionic plates and umbilical cords, are reported. GB1, GB4, GB5, GB6, GB9 and GB11 showed various reactivity patterns on the epithelial cells of amnion, chorion and skin at different stages of differentiation. In addition, GB9 and GB11 showed extracellular reactivities; GB9 detected chorionic villi which were usually surrounded by fibrinoid and GB11 reacted with fibrinoid structures in the placentae and chorion laeve. GB10 recognized connective tissues in fetal mesenchyme and adult dermis. This study demonstrates the expression of many shared antigens between tissues derived from the extra-embryonic ectoderm and adult skin. These monoclonal antibodies will provide useful tools for further investigations of epithelial differentiation and transformation.

Abnormal binding of an anti-amnion antibody to epidermal basement membrane provides a novel diagnostic probe for junctional epidermolysis bullosa

AA3 is a novel antibody raised against human amnion, which reacts with the basement membrane of various epithelia of ectodermal origin. We used AA3 to examine the epidermal basement membrane zone in normal skin and different genetically determined types of epidermolysis bullosa (EB), by indirect immunofluorescence. AA3 staining was normal in dystrophic and simplex EB, but was markedly reduced in lesional and non-blistered skin in severe forms of junctional EB. In non-lethal junctional EB, the intensity of staining was variable and appeared to be inversely associated with disease severity, but did not correlate with demonstrable abnormalities of hemidesmosomes. AA3 binding was not reduced in pemphigoid lesions or normal suction blisters. It appeared to localize to the lamina lucida, but with different characteristics compared with antibodies to laminin and bullous pemphigoid antigen. These finding suggest that AA3 recognizes an antigen (or antigens) which may be involved in a primary biochemical defect in junctional EB. Moreover, this antibody may act as a new probe for this potentially lethal mechano-bullous disease.