Chemotactic factors in the human follicle at ovulation

Abstract: Ovulation is initiated by the midcycle gonadotropin surge, which leads to a controlled degradation of the follicle wall ending in follicular rupture and oocyte extrusion. The gonadotropins triggers several biochemical and biophysical changes such as vascular alterations, increased proteolytic enzyme activity and leukocyte extravasation, within the preovulatory follicle. These events have several characteristics of an acute inflammatory reaction and ovulation is now looked upon as an inflammation-like process. A common phenomenon in inflammation is the gathering of leukocytes at the inflammatory site. In the ovary, leukocytes, especially neutrophils and macrophages, increase in numbers in the preovulatory follicle in response to the gonadotropin surge. Leukocytes may facilitate the events leading to follicular rupture at ovulation by their ability to secrete classical inflammatory/ovulatory mediators. The intra-ovarian signals causing this influx of leukocytes into the preovulatory follicle have been studied in more detail in the present study. The chemokines, a newly discovered group of chemotactic cytokines, have lately been given much attention for their specific roles in leukocyte migration and activation in inflammatory reactions and was therefore of interest as possible mediators of the ovulatory leukocyte influx. The specific aim of the present thesis were to investigate if some of these chemotactic factors, in particular the chemokines, were present in the human preovulatory follicle and if the synthesis was regulated by gonadotropins, steroids or cytokines. The concentrations of chemotactic factors in follicular fluid from preovulatory follicles of IVF-patients and follicular fluid at three stages of the natural cycle were studied. It was found that follicular fluid contained chemotactic properties of IL-8, GRO-a, MCP-1, CSF-1 and RANTES, but was devoid of the chemokine MIP-1a. The levels of the neutrophil attractant IL-8 in follicular fluid from natural cycles were increased at an early stage of the ovulatory process, while the macrophage attractants MCP-1 and CSF-1 increased at a later stage. Follicular fluid components may either be derived from the circulation or be secreted products from the follicular cells. To investigate the origin of the follicular fluid chemotactic factors, granulosa and theca cells from natural cycles were cultured and presence of chemotactic factors in conditioned media were studied. IL-8 originated from both granulosa and theca cells whereas MCP-1 and MIP-1a were more likely secretions from immune cells. The secretion of IL-8 by the granulosa cells was regulated by FSH and possibly by LH. The proinflammatory cytokines IL-1a and IL-1b were very potent in the induction of IL-8 and GRO-a secretion from follicular cells. Cultures of granulosa-lutein cells obtained from IVF cycles often contain a proportion of immune cells. In these cultures, MCP-1 was detected, indicating that immune cells contribute to the secretion of this chemokine in the ovulating follicle. In these cultures basal production of IL-8 and GRO-a but not RANTES was seen. In conclusion, the study shows that IL-8, GRO-a, MCP-1 and CSF-1 are expressed in the follicle and regulated by gonadotropins and cytokines. It is likely that they contribute to the migration and activation of leukocytes into the ovulating folllicle.