Immunochemical Study of the Structural Specificity of an Anti-Gentamycin Antiserum, Useful Also for Radioimmunoassay of Sisomycin

Abstract

At this Department a piece of collaborative work has resulted in a new method for the radioimmunoassay of gentamycin levels in biological fluids (Jonsson et al., 1974 and 1975). It differs in two important respects from the techniques applied by the first two groups in the field (Lewis et al., 1972, Mahon et al., 1973). The most important difference lies in the choice of the radioactive tracer. Since there is no commercial source supplying a reproducible preparation of tritiated gentamycin, and since it is technically much simpler to measure gamma radiation than beta radiation, a large effort was put into establishing a method for the reproducible preparation of a conjugate of gentamycin and human serum albumin (HSA). This product is easily labelled with radioactive iodine, ¹²⁵I, in a reproducible fashion without loss of the antigenic activity of the coupled gentamycin. The second difference lies in the choice of technique for the separation of antibody-bound and free antigen. We have applied a solid phase separation reagent of killed protein A-containing Staphylococcus aureus (Jonsson and Kronvall, 1974) with a high capacity for binding more than 90 per cent of the serum IgG of some mammals such as man and rabbit.