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The aim of this study was to determine the contribution of various IgG subclasses to the scintigraphic detection of a staphylococcal infection. An experimental thigh infection in mice was used to determine the accumulation of the various 99Tcm-labelled IgG preparations with enriched IgG1, IgG2 or IgG4 subclass. Multiple-regression analysis was used to investigate a relationship between the IgG subclasses and the time-dependent accumulation in infected sites. Eighteen hours after infection with Staphylococcus aureus bacteria 20 micrograms of 99Tcm-labelled IgG preparations enriched with one of the IgG1, IgG2 or IgG4 subclasses by thiophilic absorption were administered intravenously and target-to-nontarget (T/NT) ratios were determined at 15 min, 1 h, 4 h and 24 h after injection of the tracer. Moreover, the binding of these preparations to S. aureus was assessed using an in vitro bacterial pellet model as an indication for the potency of detecting infections. As a control agent, 99Tcm-labelled polyclonal IgG (HIG) was used. In vivo, the T/NT ratios were significantly (P < 0.05) higher for the IgG1-enriched preparation at all time points, and for the IgG2-enriched preparation at 4 h and 24 h after injection, compared with HIG. In contrast, IgG4 did not yield higher T/NT ratios at any time. Using multiple-regression analysis, it became evident that IgG3 at all time intervals, IgG1 for early scans (up to 4 h) and IgG2 for late scans (24 h) contribute significantly (P < 0.05) to the accumulation. The abundance of IgG subclasses in the various preparations appeared to influence the accumulation of tracer at infected sites. The percentage of binding to S. aureus in vitro was significantly (P < 0.05) higher for enriched IgG subclass preparations than for HIG. We conclude that specific subclass enrichment of 99Tcm-labelled IgG preparations improves the scintigraphic detection of staphylococcal infections at various time intervals post-injection.

This study was designed to assess monoclonal antibodies (MAbs) directed against tumor necrosis factor-alpha (TNF-alpha) (anti-TNF) or interleukin-8 (anti-IL-8) as radioactive agents for the detection of Staphylococcus aureus-or Klebsiella pneumoniae-infected thighs in mice. At 5 min (acute infection) or 20 h (established) post-infection, 20 micrograms of the 99mTc-labeled MAbs were injected. At various time intervals, the accumulation of the radiotracer in the infected thighs was assessed and expressed as a target-to-nontarget (T/NT) ratio. The binding of 99mTc-labeled MAbs to circulating mononuclear cells and granulocytes was quantitated 20 h after injection. The pharmacokinetics of the MAbs, in relation to the control agents 99mTc-labeled polyclonal human immunoglobulin (IgG) and a 99mTc-labeled nonspecific IgG1 MAb, were also studied. In acute infections, 99mTc-anti-TNF accumulated to a higher extent (p < 0.05) in S. aureus-infected thighs in mice until 4 h after the injection than 99mTc-IgG and was higher at 0.25 h in K. pneumoniae-infected mice (p < 0.03) compared with 99mTc-IgG. In established S. aureus and K. pneumoniae infections, 99mTc-anti-IL-8 detected the infection more intensely than 99mTc-IgG until 1 h after injection. In both S. aureus and K. pneumoniae infections, localization of sites of infection correlates (p < 0.05) with increased binding of the 99mTc-labeled MAbs to granulocytes and mononuclear cells in both acute and established infections. It was concluded that 99mTc-labeled MAbs, directed against TNF-alpha and IL-8, accumulate in bacterial infections in mice to a higher extent than does 99mTc-IgG after infection and is related to the binding of the antibodies to blood leukocytes. With these 99mTc-labeled MAbs, information might be gained about the development of an infection.

The purpose of this study was to assess the contribution of phagocytic cells and bacteria to the accumulation of technetium-99m labelled polyclonal human immunoglobulin (HIG) at sites of inflammation. Mice were intraperitoneally injected with Staphylococcus aureus (SA animals), with heat-inactivated newborn calf serum (NBCS, to mimic a non-bacterial inflammation) or with physiological saline (controls); 1 h thereafter they received HIG. At various intervals after the administration of HIG the mice were killed, and the percentages of radioactivity in the peritoneal effluent and attached to the cellular and bacterial fraction thereof were established. Furthermore, the total number of cells and that of bacteria in the fluid were quantitated. The percentage of activity in the effluent in the SA animals was (P < 0.02) higher than those in the NBCS-injected animals and controls from 4 h onwards. In all groups of mice this percentage was highest at 4 h and decreased (P < 0.01) afterwards. The percentage of cell-bound activity and the total number of cells remained fairly constant or increased with time in the SA animals (P < 0.01). The bacteria-bound activity remained rather constant throughout the experiment and ranged between 4% and 6%. In the SA-infected animals the percentage of cell-bound activity was correlated with the total number of cells (macrophages but especially neutrophils) but even more strongly with the number of cell-associated bacteria. In the NBCS-injected animals a correlation was demonstrated between the cell-bound activity and the total number of cells (only neutrophils).(ABSTRACT TRUNCATED AT 250 WORDS)

A new method for the labelling of mixed leucocytes with 99mTc-tropolone was optimized and compared with a 99mTc-HMPAO leucocyte labelling procedure in vitro and in vivo. In the present study, leucocytes obtained from patients suffering from Crohn's disease, were isolated and labelled with 99mTc-HMPAO or labelled according the new 99mTc-tropolone procedure using 9.8 mM tropolone, 1 microM stannous chloride and 0.8 mM potassium borohydride (KBH4) at pH 5.5-6. Labelling efficiency with 99mTc-tropolone yielded 92 +/- 3%, which is higher compared to the 99mTc-HMPAO labelling procedure (64 +/- 13%) using 10(8) of leucocytes. In vitro stability and viability of both the tropolone and the HMPAO labelled cells was investigated. The viability test of the 99mTc-labelled leucocytes was performed in autologous plasma at 37 degrees C and compared with unlabelled leucocytes. After 18 hours of incubation a significant (P < 0.05) higher stability was observed for 99mTc-tropolone labelled leucocytes (84 +/- 5%) compared with that of 99mTc-HMPAO labelled leucocytes (73 +/- 5%). The viability of the 99mTc-labelled leucocytes observed for both labelling procedures was similar to unlabelled leucocytes. In vivo experiments were performed in mice. 99mTc-tropolone or 99mTc-HMPAO labelled murine mixed leucocytes were injected in mice, with a Staphylococcus aureus ATCC 25923 thigh infection. Analysis of scintigraphic images yielded a faster clearance of the 99mTc-tropolone labelled leucocytes. This was most likely due to a significant (P < 0.02) higher liver uptake at 4 hours after administration of the 99mTc-tropolone labelled leucocytes (19%) in comparison with 99mTc-HMPAO labelled cells (9%). Faster and significant (P < 0.02) higher accumulation of the 99mTc-tropolone labelled leucocytes was observed at the site of infection compared with 99mTc-HMPAO labelled leucocytes at all time-intervals after the administration of the 99mTc-labelled leucocytes. The new 99mTc-tropolone leucocyte labelling procedure, offers an attractive low-cost agent for research purposes.

To improve the scintigraphic detection of bacterial infections a protein charge-purified fraction of polyclonal human immunoglobulin was applied as a radiopharmaceutical. This purification was achieved by attaching the immunoglobulin to an anion-exchanger column and by obtaining the column-bound fraction with buffer. The binding to bacteria in vitro and the target to non-target ratios of an experimental thigh infection with Staphylococcus aureus or Klebsiella pneumoniae in mice were evaluated to compare the purified and the unpurified immunoglobulin. The percentage of binding to all gram-positive and gram-negative bacteria used in this study was significantly (P < 0.03) higher for the purified than for the unpurified immunoglobulin. For the in vivo study, mice were infected in the thigh muscle with Staph. aureus or K. pneumoniae. After 18 h 0.1 mg of technetium-99m labelled polyclonal immunoglobulin or 99mTc-labelled protein charge-purified polyclonal human immunoglobulin was administered intravenously. At all time intervals the target (infected thighs) to non-target (non-infected thighs) ratios for both infections were significantly higher (P < 0.03) for protein charge-purified polyclonal immunoglobulin than for unpurified polyclonal human immunoglobulin. Already within 1 h the infected tissues could be detected by the purified immunoglobulin. It is concluded that 99mTc-labelled protein charge-purified immunoglobulin localizes both a gram-positive and a gram-negative thigh infection more intensely and faster than 99mTc-labelled unpurified immunoglobulin.

The present study was undertaken to compare the technetium-99m labelled non-specific polyclonal human immunoglobulin (Ig) with 99mTc-labelled monomeric human immunoglobulin (m-Ig), 99mTc-labelled, protein A-purified, human immunoglobulin (A-Ig) and 99mTc-labelled monomeric, protein A-purified, human immunoglobulin (mA-Ig) as tracer agents for the detection of a thigh infection with Staphylococcus aureus. In vitro the binding of the various tracer agents to bacteria at various intervals 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 99mTc-labelled Igs bound to bacteria in vitro: the percentages of binding for the m-Ig (from 1 h onwards) and A-Ig and mA-Ig (from 3 h onwards) were significantly higher than that for Ig. The in vivo target-to-non-target (T/NT) ratios were significantly 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 administration of m-Ig, A-Ig and mA-Ig than after administration of Ig. It is concluded that in this experimental infection 99mTc-labelled monomeric Ig localizes a staphylococcal thigh infection better and faster than 99mTc-labelled unpurified Ig. However, the accumulation obtained with protein A-purified Ig or protein A-purified monomeric Ig was the highest of all tracer agents tested.

The purpose of this study was to investigate both the ability of 99mTc-labeled polyclonal human immunoglobulin (HIG) to localize an infection and the modes of action involved in this process. Mice, infected with Staphylococcus aureus ATCC 25923 in a thigh muscle, received HIG intravenously. Scintigrams were made 1, 4, and 24 hr later; subsequently the mice were killed and the activity in several organs and thighs was determined. The radiopharmaceutical demonstrated a time-dependent accumulation at the site of infection. It was found that vascular permeability or Fc binding alone could not account for the mode of action of HIG. Neither the origin of Ig (human versus murine) nor the total amount of protein (0.01-1.0 mg Ig per mouse) affected the target-to-background (T/B) ratios. Ratios were not different for leukocytopenic animals. A correlation (p less than 0.001) was demonstrated between the number of bacteria at the site of infection and the T/B ratio. This was also found after antibiotic treatment (p less than 0.02).

The aim of the present study was to determine whether 99mTc-labelled polyclonal human immunoglobulin (99mTc-HIG) binds to bacteria in vitro as well as in vivo. In vitro, the binding of 99mTc-HIG to various gram-positive and gram-negative bacteria was determined. In vivo, mice were infected with Staphylococcus aureus Cowan I (protein A rich) or S. aureus EMS (protein A deficient) in a thigh muscle and then 99mTc-HIG or 99mTc-labelled human serum albumin (99mTc-HSA) was administered; scintigrams were made 1, 4, and 18 h later. In vitro binding of 99mTc-HIG to bacteria was higher for gram-positive than for gram-negative forms. A positive correlation was found between the protein A content and the degree of binding to S. aureus. This was also found in vivo. The accumulation of 99mTc-HIG at the site of infection was significantly (P less than 0.01) higher than that of 99mTc-HSA, for both strains of S. aureus. It is concluded that vascular permeability cannot fully explain the accumulation of 99mTc-HIG at the site of infection and that binding of 99mTc-HIG to bacteria plays a role in this respect.

The accumulation of nonspecific polyclonal human immunoglobulin G (IgG) radiolabeled with 99mTc was compared to that of [99mTc]albumin and [99mTc]nanocolloid in rats with collagen induced arthritis. Serial scintigrams were acquired directly, 4 and 24 hr after injection. A clearly discernable image of the site of synovitis was seen with [99mTc]IgG as early as 4 hr postinjection. The relative intensity of the inflammatory lesion was maximal at 24 hr. Discrimination between arthritic and nonarthritic joints as well as correlations between the relative intensity of the arthritic joint and clinical indices of joint inflammation were superior with IgG compared to albumin or nanocolloid. These studies show that localization and severity of inflammatory joint disease can be detected with radiolabeled nonspecific IgG.