Endometriosis is a common condition in which the immune response is dysregulated within the eutopic endometrium and at ectopic sites 1. The baboon (Papio anubis) is generally considered the best model of endometriosis pathogenesis, however, little is known regarding the immune response in this model 2.
To characterise immune cell populations in eutopic endometrium and peritoneal endometriotic lesions from a baboon model of induced-endometriosis.
Materials and methods
Uterine and peritoneal samples were obtained from normally cycling female baboons with (n=5) and without (n=5) induced endometriosis, on days 9-12 post ovulation. Immunohistochemical staining was performed with antibodies for all T cells (CD3), effector T cells (CD4), cytotoxic T cells (CD8), B cells (CD20) and natural killer cells (NK; CD56).
CD3+ and CD20+ cell aggregates were present in the functional layer of the endometrium in some specimens, while in the basal layer, these cells often surrounded large vessels. NK numbers in the uterus varied greatly between specimens but were most numerous in the functional layer of the endometrium. Effector T cells and cytotoxic T cells were rare in the endometrium.
CD3+ T cells were abundant and effector T cells present in endometriotic stroma of most lesions, with some infiltrating the glandular epithelium. Rare cytotoxic T, B and NK cells were observed in and around some lesions.
In the baboon model of induced-endometriosis, a range of immune cells are present in varying densities in the endometrium and myometrium, and in peritoneal endometriotic lesions. In women, the failure of the immune system to clear shed endometrial tissue and to protect the peritoneum from its adhesion and invasion is hypothesised to be involved in endometriosis establishment 3. Detailed studies of the early immune response to inoculated menstrual tissue in the baboon endometriosis model will be useful to determine the role of the immune system in endometriosis pathogenesis.