Simultaneous expression of CD13, CD22 and CD25 is related to the expression of Fc epsilon R1 in non-lymphoid leukemia.

Like CD19 or CD56, CD22 in non-lymphoid leukemia has been considered an aberrantly expressed antigen. CD22 had been believed to be restricted to B lymphoid, however, it was also found to be expressed in human basophils. Mature basophils are unique granulocytes expressing CD13, CD22 and CD25. To estimate whether the expression of CD22 in non-lymphoid leukemia is aberrant or related to basophilic character, we analyzed 108 patients with primary and secondary leukemia. Among non-lymphoid leukemias, surface CD22 expression was more frequently observed in peroxidase-negative AML and secondary leukemia, and was usually observed simultaneously with CD13 and CD25. Samples obtained from 17 cases were further analyzed, and all the Fc epsilon R1-positive cases were observed in peroxidase-negative AML and secondary non-lymphoid leukemia, and mostly expressed CD13, CD22 and CD25. Therefore, surface CD22 expression in non-lymphoid leukemia was thought to relate to basophilic phenotype in some cases. Like CD22, some of the so-called aberrantly expressed antigens may not actually be aberrant, but are expressed in a stage of differentiation and maturation of progenitors. Moreover, CD22 may be one of target molecules for treatment of CD22-positive, poorly prognostic leukemia.

Fc epsilon RI and CD22 mRNA are expressed in early B-lineage and myeloid leukemia cell lines.

CD22, one of the important markers for diagnosing B-lineage acute leukemia, was expressed in mature basophil granulocytes. We then investigated the expression of CD22 and other B cell- and basophil-related molecules in 25 human acute leukemia cell lines to find the phenotype of the virtual common progenitor of B and myeloid lineage. Surface and cytoplasmic expressions of antigens were analyzed using a flow cytometer and an essential antibody panel used for diagnosing acute leukemia as well as cytokine receptors and basophil-related enzymes. Messenger RNA expression of Fc epsilon R1 and CD22 was also analyzed. Peroxidase-positive and -negative myeloid leukemias showed eosinophil- and basophil-type expression of enzymes, respectively. Early myeloid and B-lineage cells expressed basically similar combinations of cytokine receptors and various combinations of mRNA listed above, while T-lineage cells did not. The virtual common progenitor of B and myeloid lineage cells may be defined as immature cells simultaneously expressing B and basophil phenotypes.

Activation of sphingomyelinase from Bacillus cereus by Zn2+ hitherto accepted as a strong inhibitor.

Sphingomyelinase (SMase) from Bacillus cereus has been known to be activated by Mg2+, Mn2+, and Co2+, but strongly inhibited by Zn2+. In the present study, we investigated the effects of several kinds of metal ions on the catalytic activity of B. cereus SMase, and found that the activity was inhibited by Zn2+ at its higher concentrations or at higher pH values, but unexpectedly activated at lower Zn2+ concentrations or at lower pH values. This result indicates that SMase possesses at least two different binding sites for Zn2+ and that the Zn2+ binding to the high-affinity site can activate the enzyme, whereas the Zn2+ binding to the low-affinity site can inactivate it. We also found that the binding of substrate to the enzyme was independent of the Zn2+ binding to the high-affinity site, but was competitively inhibited by the Zn2+ binding to the low-affinity site. The binding affinity of the metal ions to the site for activating the enzyme was determined to be in the rank-order of Mg2+ = Co2+ < Mn2+ < Zn2+. It was also demonstrated that these four metal ions competed with each other for the same binding site on the enzyme molecule.