Breast tumors are frequently associated with a predominantly lymphocytic infiltrate, which constitutes an immune response against the tumor. In spite of this massive infiltrate, the immune response appears to be inefficient and the tumor is able to evade it. We propose that in breast cancer, tumor escape from immunological surveillance results from the induction of apoptosis of Fas-bearing activated lymphocytes by FasL-bearing breast cancer cells. To test this proposal we studied the expression of FasL by human breast carcinomas and the MCF-7 breast cancer cell line by RT-PCR, immunohistochemistry, and Western Blot. Moreover, we describe the presence of apoptosis and Fas expression in the lymphocytic population surrounding the tumor. Strong membranous and cytoplasmic staining was detected in ductal carcinomas and hyperplastic breast tissue, but it was absent from normal breast tissue. No staining was found in normal glands in the non-tumor quadrants; however, the normal appearing ducts surrounding the carcinoma (tumor quadrant) showed intense immunoreactivity. Apoptosis was found predominantly among the lymphocytic population, as well as in the blood vessels and fibro-fatty tissue close to the tumor. Further characterization of apoptotic cells demonstrated that they were CD3+ cells. Our results suggest the breast tumors may elude immunological surveillance by inducing, via the Fas/FasL system, the apoptosis of activated lymphocytes. Recent data have demonstrated FasL RNA in other tumor types. Upregulation of FasL expression in hyperplastic and normal breast ducts close to the tumor also suggests a possible role in early neoplastic transformation and proliferation.
We propose that FasL expression in the placenta is a mechanism responsible for the development of maternal immune tolerance specific for paternal alloantigens and operates in pathologic states characterized by trophoblastic invasion/proliferation.
PROBLEM: The low frequency of maternal immune responses to paternally inherited fetal antigens raises the following question: What regulates the immunobiology of pregnancy? Data suggest that this state is the result of peripheral immune‐tolerance, an active process of immune‐regulation in which activated T cells undergo apoptosis. We studied Fas ligand (FasL) expression and apoptosis in normal and pathologic placentas to find out whether the Fas‐FasL‐induced apoptosis takes place during implantation.
METHOD OF STUDY: FasL expression in paraffin sections was detected using specific antibodies and confirmed with reverse transcriptase‐polymerase chain reaction of total RNA from frozen placentas. Apoptosis was detected using the terminal deoxy (d)‐UTP nick end‐labeling assay.
RESULTS: FasL was found in the normal placenta and in gestational trophoblastic disease. Apoptotic leukocytes were localized to the maternal‐fetal interface corresponding in localization with the distribution of FasL.
CONCLUSIONS: We propose that FasL expression in the placenta is a mechanism responsible for the development of maternal immune tolerance specific for paternal alloantigens and operates in pathologic states characterized by trophoblastic invasion/proliferation.
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