Different types of false positive anti-HIV reactions in patients on haemodialysis.

Serum samples of 589 haemodialysis patients were screened for HIV antibody by ELISA methods. Of these, 36 samples were found to be repeatedly reactive. None of the 36, however, could be confirmed by competitive enzyme immunoassays and Western blot; therefore, they were considered to be false positive. The sera could be divided in two groups. The sera of Group 1 were designated as the usual type of false positivity, caused most probably by anti-lymphocyte antibodies. In 19 sera, however, a special type of false positivity was found. These sera reacted strongly with the plates coated with the supernatants of HIV-infected cells but not with those of uninfected H9 cells. Three and two sera showed, respectively, positive immunofluorescence reaction with the HIV-infected, but not with the uninfected, H9 and CEM cells. Reactivity to HIV-infected H9 cells could be adsorbed from a part of these samples with lesser amounts of HIV-infected than uninfected H9 cells. This special type of false positivity was observed frequently (7/65) in patients who rejected a kidney graft. These findings suggest that this type of anti-HIV false positivity is due to antibodies reacting with cellular antigens present in HIV-infected but not in uninfected lymphocytes. Their appearance seems to be associated with the immunological activation occurring at graft rejection.