Mastocytoma in the common carpal sheath of the digital flexor tendons of a horse.

A 13-year-old Morgan gelding was examined for right forelimb lameness and tenosynovitis of the right common carpal sheath of the digital flexor tendons. The horse had moderate right forelimb lameness at the trot and marked effusion of the right common carpal sheath of the digital flexor tendons. Ultrasonographic examination revealed a soft tissue mass within the proximal pouch of the affected tendon sheath, located adjacent to the distal physis of the radius. Cytology and culture of the fluid revealed a sterile, eosinophilic tenosynovitis. Tenoscopic exploration confirmed the presence of a capsulated soft tissue mass. Thecotomy was required to fully debride the mass, which histology revealed to be a mast cell tumour. At 22 months postoperatively, the horse developed mild right forelimb lameness and eosinophilic tenosynovitis because of recurrence of the mastocytoma. Mastocytosis is a possible differential diagnosis in any horse exhibiting lameness associated with tenosynovitis. Surgical excision combined with rest and postoperative intrasynovial and systemic corticosteroids may be palliative.

Modeling trophoblast differentiation using equine chorionic girdle vesicles.

The chorionic girdle of the equine conceptus is comprised of specialized trophoblast cells which, at day 36-38 of equine pregnancy, gain an invasive phenotype and invade the endometrium to form endometrial cups. Studies of equine endometrial cups remain difficult to perform because of the invasive techniques required to obtain cup tissue and because sampling requires termination of the pregnancy. In this study we developed a system to model trophoblast differentiation and trophoblast-immune interactions in vitro and in vivo. We utilized a method of culturing chorionic girdle pieces in serum-free medium to promote spontaneous formation of vesicle structures enriched for terminally differentiated binucleate cells that secreted equine chorionic gonadotrophin (eCG). Immunohistochemical staining and scanning electron microscopy showed that the cells of the vesicles closely resembled the outer layers of chorionic girdle immediately prior to invasion. Chorionic girdle vesicles were harvested after 72h in culture and ectopically transplanted via injection into the vulvar mucosa of recipient mares. At 7, 14, 21 and 28days after transplantation, biopsies of the injection sites were obtained. Immunohistochemical labeling of cryostat sections of the biopsies with a panel of monoclonal antibodies to horse trophoblast molecules demonstrated survival, differentiation, and presence of trophoblast cells for at least 21days. Serial sections of the biopsies labeled with antibodies to the equine lymphocyte surface markers CD4 and CD8, together with lymphocyte microcytotoxicity assays, revealed that the recipients mounted both cellular and humoral antibody immune responses to the transplanted trophoblast cells. This new method for culturing equine chorionic girdle trophoblast cells, and for transplanting trophoblast vesicles to ectopic sites, should allow identification of key aspects of trophoblast differentiation and the interactions that occur between invasive trophoblast and the maternal immune system.