Lymphocyte subsets (CD57)

This test measures the proportion of CD57-expressing natural killer (NK) cells in the blood. It is used in reproductive immunology to investigate whether an over-abundance of these highly cytotoxic cells may be contributing to recurrent implantation failure, recurrent miscarriage, or repeated IVF cycle failure. It is most appropriate for patients who have experienced unexplained reproductive loss or unsuccessful assisted conception and for clinicians seeking to assess the uterine natural killer (uNK) cell environment before planning further treatment.

What is measured

• CD57 lymphocytes: A subset of natural killer cells that express the CD57 marker. These cells are highly differentiated, display potent cytotoxic activity, and are thought to play a role in the immune surveillance of the endometrium. Elevated levels in peripheral blood may reflect an immune environment less tolerant of an implanting embryo.

Why it matters

A successful pregnancy depends on a finely balanced immune response: enough NK cell activity to support implantation and placental development, but not so much that the embryo is rejected. An elevated CD57 NK cell proportion has been associated with poorer reproductive outcomes in some studies. Identifying this imbalance gives your clinician the information needed to consider targeted immunomodulatory strategies, such as intralipid therapy, corticosteroids, or other immune-directed treatments, and to monitor response to those interventions.