Differences between Antibodies against the Dense Sediment and Microsome Fractions of the N-2-Fluorenylacetamide-induced Rat Hepatoma¹ Free

Rabbit antibodies against the microsome and dense sediment fractions of N-2-fluorenylacetamide-induced rat hepatoma were compared in vivo and in vitro. Although both antibodies localized in the hepatomas and normal livers when injected into tumor-bearing or normal rats, clear differences in their localizing properties could be shown by various technics. The combined use of ¹²⁵I-labeled anti-microsome and ¹³¹I-labeled anti-sediment antibodies in the same mixture (paired label technic) made it possible to compare the 2 antibodies quantitatively under strictly identical conditions. The localization in vivo of the anti-microsome antibodies was greatly reduced by treatment with the hepatoma microsomes, but no effect was observed on the localization of anti-sediment antibodies. When the hepatomas from the injected rats were fractionated into subcellular fractions, it was found that the microsome fraction contained a larger proportion of the anti-microsome antibodies than of the anti-sediment antibodies, whereas the dense sediment fraction contained a larger proportion of the anti-sediment antibodies than of the anti-microsome antibodies. The 2 antibodies also behaved differently when their localization was examined as a function of time. The anti-microsome antibodies seemed to localize and be eliminated more rapidly than the anti-sediment antibodies.

These differences were clearly reflected in their sites of localization as determined by radioautography of tissue sections from rats which had been injected with ¹²⁵I-labeled antiserum globulins. The anti-microsome antibodies localized preferentially on the sinusoidal walls and on the hepatoma cells and normal hepatic cells. In contrast, the anti-sediment antibodies localized heavily in the connective tissues and lightly on the sinusoidal walls, but not on the hepatoma or normal hepatic cells.

Staining tissue sections in vitro by the fluorescent antibody technic showed that the anti-microsome antibodies were directed against the components of the hepatic cells and the anti-sediment antibodies against the components of the connective tissues.