Immune-surveillance and programmed cell death-related genes are significantly overexpressed in the normal breast epithelium of postmenopausal parous women.

Endocrine and reproductive influences significantly affect the lifetime risk of breast cancer. Nulliparity is one of the most firmly established risk factors for breast cancer, whereas early full-term pregnancy and parity confer a significant protection. The breast attains its maximum development during pregnancy and lactation. After menopause the breast regresses in both nulliparous and parous women containing lobular structures designated lobules type 1 (Lob 1). We have postulated that the degree of differentiation acquired through early pregnancy changes the 'genomic signature' that differentiates the Lob 1 from the early parous women from that of the nulliparous women by shifting the Stem cell 1 to a Stem cell 2, making this the mechanism of protection conferred by early full-term pregnancy. In order to elucidate the molecular pathways through which pregnancy exerts a protective effect, we have analyzed the genomic profile of Lob 1 present in reduction mammoplasty specimens obtained from parous and nulliparous postmenopausal women. The genes differentially expressed are related to immune-surveillance, DNA repair, programmed cell death, transcription, and chromatin structure/activators/co-activator. In the present study we performed real-time RT-PCR using a low-density array or a microfluid card for genes related to the immune system and programmed cell death, using 18S as an internal control [TaqMan(R) Low Density Array Human Immune Panel (Applied Biosystems)]. Breast epithelial cells from parous women significantly overexpressed 17 out of 20 genes (p<0.001) with respect to the nulliparous breast. BCL2-associated X protein, Complement component 3, CD45 antigen, glyceraldehyde-3-phosphate dehydrogenase, granulysin, and chemokine (C-C motif) ligand 19 were expressed more than 30-fold with respect to nulliparous breast cells. Only three out of 20 genes [selectin P (granule membrane protein 140 kDa, antigen CD62), Fas (TNF receptor superfamily, member 6) and chemokine (C-X-C motif) ligand 11], were downregulated in parous breast with respect to nulliparous breast cells. The data lead us to conclude that an early pregnancy, by shifting the Stem cell 1 to Stem cell 2, makes the latter more easily recognized by the immune-surveillance system, which initiates the programmed cell death pathway if exposure to toxic or carcinogenic agents occurs.