Expression of the CDw75 (beta-galactoside alpha 2,6-sialyltransferase) antigen on normal blood cells and in B-cell chronic lymphocytic leukaemia.

Using monoclonal antibodies (mAb) characterized at the last International Workshop on Human Leucocyte Antigens, we examined the expression of CDw75 antigens (beta-galactoside alpha 2,6-sialyltransferase) on normal peripheral blood cells and on cells from patients with B-cell chronic lymphocytic leukaemia (CLL). The mAb used (HH2, EBU.65, EBU.141 and OKB4) detect different epitopes of CDw75. Normal peripheral blood B cells expressed high levels of CDw75 detectable with HH2, EBU.65 and EBU.141 but did not react with OKB4. Cells from patients with B-cell CLL closely resembled normal B cells. All CDw75 epitopes, including OKB4, were strongly expressed on some Namalwa variant Burkitt lymphoma cell lines. The OKB4 epitope was also present on red cells from all normal donors. The other CDw75 mAb were unreactive with red cells from some normal donors. The CDw75 epitope detected with EBU.65 was present on most CD4+ T cells and on a minority of CD8+ cells. HH2 and EBU.141 stained only small numbers of T lymphocytes. OKB4 did not react with T cells. EBU.65+, CD4+ T cells had low levels of expression of CD45R0, CD29, CD54 and CD58, and had high levels of CD45RA antigen. Phytohaemagglutinin (PHA) activation of cells led to the loss of EBU.65 binding. These results suggest that the CDw75 epitope recognized by the EBU.65 mAb is a marker of native T lymphocytes. On B CLL cells the epitopes detected with HH2, EBU.65 and EBU.141 were destroyed by treatment with neuraminidase. Treatment of B-CLL cells and red cells with neuraminidase increased the binding of OKB4, suggesting that this epitope is masked by sialic acid. The results suggest that CDw75 is a sialylated cell-surface antigen expressed in a number of tissue-specific isoforms.