Histologie Distribution and Biochemical Properties of α1‐Microglobulin in Human Placenta

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Abstract
PROBLEM: The embryo is protected from immunologic rejection by the mother, possibly accomplished by immunosuppressive molecules located in the placenta. We investigated the distribution and biochemical properties in placenta of the immunosuppressive plasma protein α1‐microglobulin.METHOD OF STUDY: Placental a α1‐microglobulin was investigated by immunohistochemistry and, after extraction, by electrophoresis, immunoblotting and radioimmunoassay.RESULTS: α1‐Microglobulin staining was observed in the intervillous fibrin and in syncytiotrophoblasts, especially at sites with syncytial injury. Strongly stained single cells in the intervillous spaces and variably stained intravillous histiocytes were noted. Solubilization of the placenta‐matrix fraction and placenta membrane fraction released predominantly the free form of α1‐microglobulin, but, additionally, an apparently truncated form from the placenta‐membrane fraction. The soluble fraction of placenta contained two novel α1‐microglobulin complexes.CONCLUSIONS: The biochemical analysis indicates the presence in placenta of α1‐microglobulin forms not found in blood. The histochemical analysis supports the possibility that α1‐microglobulin may function as a local immunoregulator in the placenta.