The
monoclonal antibodies (MoAbs) CD22 and CD11c recognize B-lymphocyte- and monocyte-associated
antigens, respectively. Reports indicate that when these two MoAbs co-express, they represent a unique marker for
hairy cell leukemia (HCL) although neither is specific for that disease. The authors evaluated the expression and diagnostic utility of CD22 and CD11C in specimens from 26 normal subjects, 29 patients, with various nonlymphoproliferative disorders (NLPDs), and 75 patients with different types of chronic
lymphoproliferative disorders (
CLDs) using two-color flow cytometric analysis of peripheral blood lymphocytes. Lymphocytes co-expressed CD22 and CD11c in less than or equal to 3% of the normal subjects and in less than or equal to 6% of the patients with NLPDs. These markers were expressed in greater than 10% of the lymphocytes of 46% (32/69) of the patients with B-cell
CLDs:
B-cell chronic-lymphocytic leukemia, 9/41; B-cell
non-Hodgkin's lymphoma, 8/14; HCL, 11/11; B-cell
lymphoproliferative disorder (NOS), 1/2; and
B-cell prolymphocytic leukemia, 1/1. None (0/6) of the lymphocytes of patients with T-cell
CLDs expressed greater than 10% CD22-positive (CD22+) or CD11c-positive (CD11c+) cells. The HCL cases demonstrated a unique CD22+CD11c+ fluorescence histogram pattern, distinct from other
lymphoproliferative disorders, that was characterized by uniformly intense CD11c and CD22 fluorescence. Differences in the expression of the CD22+CD11C- and CD22+CD11C+ phenotypes between diagnostic groups were found, most notable was a paucity of CD22+CD11c+ cells in lymphocytes of patients with HCL. CD22 also had more variable expression than CD19 and
HLA-DR in the cases of B-cell CLD. This study demonstrates that the CD22+CD11c+ phenotype is not unique to HCL but is a consistent feature of that disorder and that the immunofluorescence pattern of co-expression in HCL is diagnostically useful.