Macrophage secretory products and sperm zona pellucida binding

To determine if exposure of human gametes to macrophage secretory products reduces sperm binding to the zona pellucida, and to determine which cytokine(s) may be responsible for this effect.

A human macrophage cell line was cultured and either activated with lipopolysaccharide for 2 hours and then washed or left unactivated. Culture-conditioned media from activated or unactivated cells was used in hemizona assay. Hemizonae were incubated with sperm suspended in culture medium from either unactivated macrophages or activated macrophages, with the matching hemizona incubated with sperm suspended in control medium. Matching hemizonae were incubated with sperm suspended in unactivated macrophage medium paired with sperm suspended in activated macrophage culture medium. Conditioned medium from activated macrophages was found to have elevated levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta, and transforming growth factor-beta, therefore, gametes were also exposed to these cytokines followed by the hemizona assay. After each incubation, the number of sperm tightly bound to the outer surface of each hemizona was determined.

Exposure of gametes to activated and unactivated macrophage culture-conditioned media significantly decreases sperm binding to the zona pellucida, with medium from activated macrophages inducing the greatest effect (P < .05). Exposure of sperm to TNF-alpha significantly impaired sperm binding (P < .05), whereas other cytokines tested had no effect.

These results suggest that macrophage secretory products in the basal and activated state may be a factor in endometriosis-associated infertility through the interference of sperm binding to the zona pellucida, and that TNF-alpha is a key cytokine responsible for this effect.