Different expression of CD3 and CD22 in leukemic cells according to whether tested in suspension or fixed on slides

The expression of antigens detected by monoclonal antibodies of the CD22 and CD3 groups was studied, by immunofluorescence (IF) on cell suspension and by immunoperoxidase (IP) on cells fixed on cytospin slides, in a range of B- and T-cell malignancies. CD22 was demonstrated in the B-cell leukemias more frequently by IP than by IF; in B-lineage acute lymphoblastic leukemia (ALL) it was positive only by IP. In chronic lymphocytic leukemia and lymphoplasmacytic tumors approximately 40% of cases were CD22 positive by IP but few by IF. In other disorders of mature B cells, CD22 was positive by both methods in most cases. CD3 was demonstrated by IP in all 48 cases of T-cell leukemia and lymphoma regardless of the maturation stage (i.e., from early thymic to mature T cells). This was not the case by IF, where only 16% of T-ALL and 73% of cases with postthymic T-cell leukemias were recorded as positive. The greater reactivity of CD3 and CD22 by IP reflect the early cytoplasmic expression of the antigens in immature T and B cells, respectively, as well as the possible greater sensitivity of the IP method. These differences should be taken into account when describing results in lymphoid malignancies. CD3 was not expressed in cells from any of the B-cell leukemias, and likewise, CD22 was not demonstrated in any of the T-cell disorders, confirming that both reagents are highly specific for their respective lineages.