IMPROVED DETECTION OF A STAPHYLOCOCCAL INFECTION BY MONOMERIC AND PROTEIN A-PURIFIED POLYCLONAL HUMAN-IMMUNOGLOBULIN

The present study was untertaken to compare the technetium-99m labelle d non-specific polyclonal human immunoglobulin (Ig) with Tc-99m-labell ed monomeric human immunoglobulin (m-Ig), Tc-99m-labelled, protein A-p urified, human immunoglobulin (A-Ig) and Tc-99m-labelled monomeric, pr otein A-purified, human immunoglobulin (mA-Ig) as tracer agents for th e detection of a thigh infection with Staphylococcus aureus. In vitro the binding of the various tracer agents to bacteria at various interv als was determined. For the in vivo evaluation, mice were infected and received one of the various labelled proteins. Scintigrams,were made 0.25, 1, 4 and 24 h later. All Tc-99m-labelled Igs bound to bacteria i n vitro: the percentages of binding for the m-Ig (from 1 h onwards) an d A-Ig and mA-Ig (from 3 h onwards) were significantly higher than tha t for Ig. The in vivo target-to-nontarget (T/NT) ratios were significa ntly higher from 4 h onwards for all purified Igs than for Ig. Protein A-purified Igs yielded higher T/NT ratios than m-Ig. Furthermore, the amount of activity in the liver was significantly lower 24 h after ad ministration of m-Ig, A-Ig and mA-Ig than after administration of Ig. It is concluded that in this experimental infection Tc-99m-labelled mo nomeric Ig localizes a staphylococcal thigh infection better and faste r than Tc-99m-labelled unpurified Ig. However, the accumulation obtain ed with protein A-purified Ig or protein A-purified monomeric Ig was t he highest of all tracer agents tested.