Comparison of the radiochemical behaviour and biological efficacy of three 99mTc-HIG preparations.

The aim of the present study was to evaluate whether the different methodologies used for human polyclonal immunoglobulin (HIG) preparation can affect the radiochemical purity of 99mTc-HIG and its binding affinity to infection sites. Three intravenous immunoglobulin preparations, beta-propiolactone treated, hydrochloric acid/pepsin treated, and an unmodified HIG molecule were studied. The HIG preparations were analysed by size-esclusion HPLC. The UV chromatogram profiles obtained showed some percentage of polymeric and dimeric fractions in all of them. The three HIG studied were directly radiolabelled via 2-mercaptoethanol reduction. Lyophilized kits containing 1 mg of HIG and a small amount of MDP(Sn) solution were prepared and then radiolabelled by adding pertechnetate-99m. The radiolabelled products, evaluated by ITLC, showed high radiochemical purity and in vitro stability. Biodistribution studies were performed in mice with an infection in the right thigh induced by the im administration of a single isolate of S. aureus, in order to compare the ability of 99mTc-HIG to detect an infectious focus. This study suggests that any damage during immunoglobulin treatment can influence the in vivo behaviour of 99mTc-HIG.