Mechanisms and physiological implications of leucocyte chemoattraction into periovulatory ovine follicles

Leucotactic polypeptide was isolated from follicular-conditioned incubation media by ultrafiltration and reverse-phase high performance liquid chromatography. The bioactive fraction was subjected to amino acid analysis and shown to be abundant in glycine, proline and hydroxyproline. These amino acid residues are common to repetitive sequences of alpha collagens. Synthetic collagen-like peptides composed of repeating triplets of glycine, proline and hydroxyproline (GPH x 3, GPH x 9) were active in attracting white blood cells as measured in vitro using a linear under-agarose assay. Accumulation of leucocytes within extravascular spaces of the theca interna was induced by intrafollicular injection of GPH x 3 or bacterial collagenase. Intrafollicular administration of affinity-purified GPH x 3 antibodies during the immediate preovulatory period inhibited thecal extravasation of leucocytes, but did not negate follicular rupture. However, serum concentrations of progesterone were depressed in antibody-treated animals throughout the ensuing luteal phase. This luteal defect was counteracted by injecting leucocytes into the preovulatory follicle. It is concluded that periovulatory follicles of the sheep secrete collagen-like leucotactic peptides. Once drawn into the follicle, resident inflammatory cells are apparently involved in transforming it into a fully functional corpus luteum.