Immunoreactivities of human isoferritins

We have examined the immunoreactivities of antisera prepared against ferritins from human liver and HeLa cells to tissue ferritins and to individual isoferritins. In a radioimmune assay for HeLa ferritin the cross-reactivity of liver ferritin was about 2.5%. However, the apparent recovery of liver ferritin in the presence of different levels of HeLa ferritin was very much greater than that predicted from the measured cross-reactivity. This anomalous behaviour was eliminated by absorption of the HeLa antiserum with L-rich ferritins, suggesting that it represented interaction with common determinants in H and L subunits. The relative levels of H and L determinants measured by radioimmunoassay in individual isoferritins correlated with their relative contents of H and L subunits. However, in some parts of the isoferritin spectrum, the radioimmunoassay underestimated the H subunit content of L-rich isoferritins and overestimated the H subunit content of L-rich isoferritins and overestimated the H subunit content of H-rich isoferritins. This finding suggests differential expression of determinants in the various heteropolymers. These could arise from conformational changes leading to exposure or internalization of different determinants, or to recognition of determinants from certain subunit interactions.