Five selected sera of patients with Burkitt's lymphoma, giving highly positive membrane immunofluorescence reactions against biopsy specimens of Burkitt cells, were negative when tested against normal bone marrow cells from donors of the same Burkitt lymphoma cells. One highly positive serum donor (Mutua) is now in chemotherapeutically induced regression and free of all signs of disease 30 months after therapy began. Mutua was selected for particular study. His sera gave highly positive reactions against biopsy specimens of Burkitt cells from 13 different donors, while the cells of 3 donors reacted more weakly. Leukoagglutination, lymphocytotoxicity, and membrane fluorescence tests against selected leukocytes and bone marrow cells of French donors with previously determined leukocyte groups gave negative results. These data indicate that the reactivity against the Burkitt target cells is probably not due to iso-antibody. Sera of 3 patients were highly positive against biopsy specimens of Burkitt cells during the first year after chemotherapeutically induced tumor regression, but had conspicuous decrease or even complete disappearance of reactivity during the second year. Tests on cells of established Burkitt tissue-culture lines Jijoye, B35M, EB3, and SL1 gave strong reactions with Mutua's serum. The reactivity of Mutua's serum against cells of these tissue culture lines was found to reside, at least in part, in the IgG fraction, as demonstrated by the use of a fluorescein-conjugated goat antiserum, directed against purified human IgG heavy chain. Three other lines of Burkitt origin, Kudi, Ogun, and Raji, were negative with Mutua's serum. Other established tissue culture lines, 7 derived from various acute leukemias arising in the United States, and 1 from the buffy coat of peripheral blood in a normal individual (Daniels), were all negative. Biopsy specimens from 2 African lymphosarcomas of non-Burkitt type, and bone marrow aspirates from 3 patients with acute leukemia arising in the United States were also negative with Mutua's serum. © 1967, Oxford University Press.
