Over 100 cell surface markers have been identified through the use of monoclonal
antibodies. Many of these markers have proven useful in identifying
a specific subpopulation of cells within a mixed colony. Accordingly, these
molecules have been assigned a “cluster of differentiation” (CD) designation.
T lymphocytes displaying the natural killer (NK) cell marker CD57 (also designated
Leu7) on their cell surface are distinguishable from other T cell subsets
by their granular lymphocyte morphology and their clonal expansion
in patients with AIDS and in recipients of bone marrow transplantation. CD57+
cells have also been shown to localize to sites of certain tumors and large
numbers of these cells are detected in the synovial fluid from patients suffering
from rheumatoid arthritis.