Inhibitory effects of horse serum on immunoassay of horse ferritin.

The effects of horse serum on the immunoassay of horse ferritin were investigated using two sandwich enzyme-linked immunosorbent assay (ELISA) systems. In System A, affinity-purified antibody to horse spleen ferritin and its conjugate with alkaline phosphatase were used as the first and second antibodies, respectively. In System B, whole antiserum and its conjugate with the enzyme were used. The recoveries of horse spleen ferritin added to horse sera were very low in either system (50-71% in System A; 42-79% in System B). However, heat treatment of the sera at 75 degrees C for 15 min improved the recoveries (90-96%) in System A, whereas the recoveries in System B were not sufficiently improved by the same treatment (75-83%). The apparent concentrations of ferritin in adult and newborn horse sera increased after heat treatment of the samples. From these results, it is concluded that horse serum contains the heat-unstable substance(s) which inhibits the immunoassay of horse ferritin.