A haemolytic plaque forming assay for identifying cells producing anti-DNA antibodies.

A murine hybridoma cell line (aDNA35I9) secreting anti-DNA antibodies was used as a model for haemolytic plaque forming cells in an assay where DNA-conjugated sheep red blood cells (DNA-SRBC) were used as target cells. DEAE-dextran, employed to abolish the anti-complementary activity of agar gel, completely inhibited anti-DNA plaques. This problem was solved by using agarose instead of agar. Since the occurrence of small plaques may make reading of the test difficult, it was established that plaque size could be increased by decreasing the antigen density on the target cells. Free DNA in the gel inhibited plaque formation, indicating the specificity of the assay. Spleen cells from mice of the strains MRL/MP and NZB/W which are known to develop a stage of autoimmunity, produced plaques in numbers which were correlated to the age of the mice and to the anti-DNA antibody level in serum.