CD45 (lymphocyte common antigen) is a receptor-linked protein tyrosine phosphatase that is expressed on all leucocytes, and which plays a crucial role in the function of these cells. LCA antibody recognizes an antigen found on lymphoid cells. It reacts with B-cells, T-cell subtypes, monocytes, macrophages, and is weakly expressed with granulocytes. CD (cluster of differentiation) is used to aid the differential diagnosis of undifferentiated neoplasms, whenever lymphoma is suspected. This antibody is expressed almost exclusively by cells of hematopoietic lineage and is present in most lymphocytes. Therefore, anti-CD45 LCA is directed against CD45 and may be used to aid in the identification of normal and abnormal cells of leukocytic lineage and as an aid in the diagnosis of anaplastic tumors.