Leukocyte origin and profile in follicular aspirates at oocyte retrieval.

BACKGROUND Follicular aspirates represent a snapshot in time of conditions within the follicle at oocyte retrieval in women undergoing in vitro fertilization and embryo transfer. This clinical material has been much investigated and yet its cellular composition remains unclear. In this study we investigated the origin and profile of leukocytes found within follicular aspirates. METHODS We performed morphological and immunohistochemical analyses of follicular aspirates and peripheral blood obtained concurrently at oocyte retrieval. RESULTS There was no correlation between erythrocyte and leukocyte numbers in follicular aspirates. The profile of leukocyte subtypes within follicular aspirates was variable and differed significantly from the peripheral circulation in a significant proportion of the analysed samples. A subset of follicular aspirates displayed a marked increase in monocytes/macrophages and an apparent concomitant reduction in polymorphonuclear leukocytes compared with peripheral blood. CONCLUSIONS Leukocytes within follicular aspirates cannot be accounted for solely as a result of blood vessel damage during oocyte retrieval. The variation in leukocyte subtypes observed in some follicular aspirates may reflect a coordinated infiltration of these cells, characteristic of progressive inflammatory responses in other systems. The possibility that leukocyte variation is indicative of follicular maturation deserves further investigation due to its potential relevance in optimizing oocyte selection.