PRESENCE OF A DYSFUNCTIONAL FORM OF CD59 ON A CD59(-LINE() SUBCLONE OF THE U937 CELL)

U937 cells are known to be relatively sensitive to C-mediated killing and have been reported to show variable expression of CD59. We have ob tained stable CD59(+) and CD59(-) sublines of the U937 cell line. Expr ession of other C-regulatory proteins, decay-accelerating factor (DAF) , MCP and CR1, was similar on bath cell lines. Although the sublines w ere morphologically similar and expressed similar amounts of most surf ace antigens, qualitative difference in expression of CD13 and CD64 an d a quantitative difference in CD15 expression was observed. Sensitivi ty to C-mediated killing of the cell lines was measured using classica l pathway activation. Both cell lines appeared to be equally sensitive to C-mediated killing. Monoclonal antibodies against CD59, which neut ralize CD59 and enhance killing of most cell lines (including K562, HL 60 and Molt4), did not enhance the killing of the CD59(-) cells but, s urprisingly, also did not enhance killing of the CD59(+) U937 subline. CD59 was expressed on the U937 subline at similar levels to that on H L60 and K562 cells, was glycosylphosphatidylinositol (GPI) anchored an d could be immunoprecipitated from cell extracts. However, unlike thes e other cell lines, U937 cell extracts were negative in a Western blot using a variety of anti-CD59 antibodies even when ultrasensitive dete ction methods were used. These results indicate that the CD59(+) U937 cell expresses a form of CD59 which is dysfunctional and structurally abnormal.