Intraepithelial and stromal lymphocytes in the normal human prostate

Background: The distribution and significance of lymphocytes in the normal human prostate is uncertain. It may be important as a determinant of the immune response, playing a role in hyperplasia and carcinogenesis.

Methods: We studied 28 normal autopsy prostates from patients between 1 and 64 years of age. Cases with nodular hyperplasia, intraepithelial neoplasia, cancer, and florid prostatitis were excluded. Each prostate was routinely processed to paraffin and immunohistochemically stained for CD20, CD45, and CD45RO. Three frozen samples obtained from these cases were stained for CD8 and CD4. One low power field (25 x magnification, 50 mm(2)) was randomly chosen for examination from each anatomic zone of the prostate, namely the peripheral, transition, and central zone. Lymphocytes were visually counted in the stroma and epithelium of each zone. Lymphocyte counts were converted to number of cells per square millimeter based on the area of the slide per field and the percentage of field that was glandular.

Results: Stromal lymphocytes were more numerous than epithelial lymphocytes (mean, 7.32 and 2.04 cells/mm(2), respectively). They were mostly T cells (stromal lymphocytes: 93% CD45RO +; epithelial lymphocytes: 99% CD45RO +). Helper/inducer (CD4 +) T cells predominated in the stroma, whereas those in epithelium were chiefly cytotoxic/suppressor (CD8 +). No difference was found in the number of stromal and epithelial T or B cells according to patient age, race, or location within the prostate (peripheral, central, and transition zones) (all P > 0.05), although the number of lymphocytes in the peripheral zone tended to exceed that in the other zones after correcting for gland:stroma ratio.

Conclusions: The immune response in the prostate is primarily cell-mediated. Cell distribution is constant according to patient age, race, and anatomic zonal location within the prostate. The greatest concentration is in the stroma with a small but significant number of intraepithelial cells. The inverted CD4/CD8 ratio in the intraepithelial compartment suggests that cytotoxic/suppressor T cells are the first line of defense against luminal foreign agents reaching the prostate through retrograde flow.