After ovulation and in the absence of fertilization, the human corpus
luteum regresses in an orderly sequence of morphological changes. This
study demonstrated that luteal regression involved progressive infilt
ration of lymphocytes and macrophages. The inflammatory infiltrate beg
an in the theca externa and gradually invaded granulosa cells, with ma
ximum accumulation of lymphocytes and macrophages at the time of menst
ruation. Immunoperoxidase staining showed that the majority of lymphoc
ytes were CD2(+), CD3(+), CD8(+) T lymphocytes, and 15% of these T cel
ls expressed perforin, a cytolytic protein implicated as a mediator of
cytotoxicity. The remaining mononuclear infiltrate showed strong reac
tivity with monocyte/macrophage markers. These findings indicate that
(a) a physiologic cell-mediated inflammatory process in the regressing
human corpus luteum is mediated mainly by CD8(+) T lymphocytes and ce
lls of monocyte/macrophage lineage and (b) perforin expression in T ly
mphocytes supports a possible role for cytolytic T cells during the ph
ysiologic inflammatory response in human luteolysis.