Got to admit you stumped me on this one, so I had to Google only to not find much. Best guess would be some measure of Lymphocytes.
www.medicinenet.com/complete_blood_count/page2.htm
- White blood count is comprised of several different types that are differentiated, or distinguished, based on their size and shape. The cells in a differential count are granulocytes,
lymphocytes, monocytes, eosinophils, and basophils.
www.medterms.com/script/main/art.asp?articlekey=4220
- A small white blood cell (leukocyte) that plays a large role in defending the body against disease.
Lymphocytes are responsible for immune responses. There are two main types of lymphocytes: B cells and T cells.