Cluster of differentiation 2 (CD2) is a useful early T-cell lineage restricted antigen that is present in T-cell differentiation. T-cell surface antigen CD2 (CD2) is a T-cell specific surface glycoprotein that is critically important for mediating adherence of T cells to antigen-presenting cells or target cells. It interacts with lymphocyte function-associated antigen (LFA-3) and CD48/BCM1 to mediate adhesion between T cells and other cell types. CD2 is involved in triggering T cells, and the cytoplasmic domain is involved in signaling. CD2 is a pan T-cell marker. CD2 antibody labels T-cell, thymocytes and natural killer (NK) cells. As a pan-T-cell marker, CD2 staining is used for recognizing practically all normal T-cells, but may be deleted in some T-cell neoplasms. Since CD2 is present in most precursor and mature T-cell leukemias and lymphomas, it is useful in the evaluation of lymphoid malignancies. By using CD2 and CD25 staining, the recognition of systemic mastocytosis and mastocytic leukemia is supported.