The human CD66 antigens CD66a, b, c, e belong to the family of carcinoembryonic antigen–related cell adhesion molecules (CEACAM). They are involved in numerous cellular processes, including cell adhesion, activation, proliferation, differentiation, survival, and apoptosis. CD66a (also known as CEACAM1, BGP, NCA-160, and C-CAM) is expressed by certain epithelial, endothelial, and hematopoietic cells. Among leukocytes, it is highly expressed on neutrophils. Upon activation, cell surface expression of CD66a is upregulated on various leukocytes, including granulocytes, T cells, and NK cell subsets. CD66b (CEACAM8, NCA-95, CGM6) is also expressed on granulocytes, CD66c (CEACAM6, NCA-50/90) is found on on granulocytes and epithelial cells. CD66e (CEA, CEACAM5) is over-expressed in certain tumors of epithelial origin.
Neutrophils play a prominent role in the innate immune response through their phagocytic activity. They are abundant in peripheral blood but almost absent in healthy tissue. Upon infection, large numbers of neutrophils are recruited to the sites of inflammation.