INTRODUCTION

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Peritonitis is often caused by ulcers, appendicitis, diverticulitis, ileus (bowel obstruction), gunshot or stab wounds, and disturbances during abdominal surgical procedures (8), allowing the escape of indigenous bowel bacteria into the peritoneal cavity (28, 45). Nosocomial peritonitis is caused by exogenous pathogenic bacteria, including Pseudomonas aeruginosa (7, 24), Staphylococcus aureus (36), and Staphylococcus epidermidis (28, 39, 44), that gain access to the abdominal cavity during prolonged surgical procedures or via a port of entry such as that created for continuous ambulatory peritoneal dialysis (CAPD) (45). These pathogens cause nosocomial peritonitis at even higher rates in immunocompromised (46) and geriatric populations when compared to typical patients (44), resulting in a significant, growing medical problem impacting both patient mortality and rising health care costs (38).

The current treatment regimen for peritonitis relies on the use of intravenous antibiotics: penicillin, third- and fourth-generation cephalosporins, or quinolones (3, 24, 28, 33, 45). Selection of antibiotics is complicated by uncertainties surrounding the identification of infecting pathogens in a mixed contaminating flora and a documented lack of correlation between in vitro antibiotic studies of pathogen susceptibility and antibiotic efficacy in clinical settings (13, 14, 24). However, initial antibiotic therapy for severe intra-abdominal infection fails in 20 to 40% of all cases, leading to additional antibiotic use (34).

Antibiotic resistance occurs at a significant rate (33) among intra-abdominal infections, and this condition is frequently associated with clinical failure (9). The increasing emergence of antibiotic is a resistant bacteria coupled with increasing immunocompromised and elderly patient populations significant incentives prompting development of new anti-infective therapies. Among many therapeutic approaches, the use of systemic intravenous immunoglobulins (IVIG) has shown promising but inconsistent results in preventing P. aeruginosa and other bacterial infections (4, 5, 7, 20, 25, 26, 29, 42, 43). Early studies reported therapeutic benefit against CAPD-associated peritonitis by using pooled human immunoglobulin G (IgG) added directly to dialysate fluid (17, 25, 26). No other local applications of immunoglobulins to treat peritonitis are known, although a recent publication supports local use of injected IVIG subcutaneously in treating P. aeruginosa burn infection (10).

This study explores the feasibility of using locally delivered pooled human IgG applied directly to the peritoneal cavity as a potential therapeutic complement or alternative to the antibiotic treatment of peritonitis. IgG delivered to a contaminated tissue site immediately opsonizes invading bacteria, promoting subsequent pathogen agglutination and, stimulated by cytokines and chemotactic factors, killing by invading macrophages and neutrophils (11, 22, 23). Major advantages of locally delivered polyclonal IgG include its application in controlled dosage formulations directly to infected sites and its ability to clear infection independently of antibiotic resistance mechanisms.

The aim of this study was to determine the prophylactic efficacy of locally applied, pooled human IgG against intra-abdominal challenges of different P. aeruginosa strains. Both in vitro and murine in vivo data support the use of pooled polyclonal IgG to neutralize P. aeruginosa in the host peritoneal cavity, preventing the systemic spread of bacteria, as well as sepsis and mortality.

	MATERIALS AND METHODS

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Animals. Female CF-1, CD-1, and CFW mice (22 to 24 g) were purchased from Charles River Laboratories (Raleigh, N.C.). All animals were acclimated for 7 days, given food and water ad libitum, and kept on a 12-h light-dark cycle. The Gristina Institute's Animal Care and Use Committee approved all of the animal procedures in this study.

Bacteria. P. aeruginosa strains (IFO-3455, obtained from A. S. Kreger [27]; M-2, obtained from I. A. Holder [30]; and MSRI-7072, a local hospital clinical isolate) were grown for 18 h in 20 ml of Trypticase soy broth at 37°C while agitated at 150 rpm in a benchtop incubator shaker. Cultured bacteria were twice sedimented by centrifugation at 7,649 × g for 10 min, washed, and diluted in saline to obtain a concentrated bacterial suspension. Serial bacterial dilutions were plated on Trypticase soy agar (TSA), and colonies were counted after 24 h of incubation at 37°C to determine initial CFU per ml. In parallel, the optical absorbance of these dilutions was measured with a Beckman DB-GT grating spectrophotometer ( = 650 nm, visible-light filter). Standard curves plotting optical absorbance versus CFU concentrations were then constructed. Typically, bacterial suspension absorbance ranges of 0.46 to 0.9 resulted in ~10⁹ CFU/ml. Heat-killed P. aeruginosa M-2 was produced by incubating these bacterial cultures at 56°C for 3 h and plating 100 µl of the 10⁷ CFU/ml stock solution on TSA to confirm nonviability.

Murine peritoneal infection model. The peritonitis model involved injecting mice with either live or heat-killed P. aeruginosa in 500 µl (IFO-3455, 90% lethal dose [LD₉₀] = 10⁷ CFU; M-2, LD₉₀ = 10⁷ CFU; MSRI-7072, LD₅₀ = 10⁷ CFU) intra-abdominally by using a syringe with a 30-gauge needle. The infectious challenge was followed immediately by a separate 500-µl colocalized abdominal injection of IgG (therapy) or either human serum albumin (HSA; lot 66H9306; Sigma, St. Louis, Mo.), 0.2 M glycine, or 5% dextrose as placebo treatments. Mortality studies involved the intra-abdominal injection of P. aeruginosa; animal survival was assessed over a 10-day period postchallenge, and survival outcomes in the treatment and control groups were compared.

Immunoglobulin therapy. Commercially pooled human IgG (lot 2620M039A, Gammagard; Baxter International, Inc., Deerfield, Ill.) was diluted in 5% dextrose (recommended by the manufacturer) to obtain the various IgG concentrations used in these trials. An anti-human IgG enzyme-linked immunosorbent assay (ELISA) (18) was used to determine polyclonal human IgG titers against three different P. aeruginosa strains. Titer numbers express the inverse log dilution of the IgG concentration at a 50% ELISA optical absorbance (450 nm) from the infection midpoint on each IgG-bacterium binding curve. Higher titer numbers reflect increased IgG binding to each bacterial strain. A second ELISA with a mouse anti-human IgG capture antibody and peroxidase-conjugated anti-human IgG detection antibody (products 209-005-088 and 209-035-088; Jackson Immunoresearch Laboratories, Inc.) was used to detect human IgG (optical absorbance at 450 nm) in mouse serum and peritoneal lavage samples as described below.

Quantitative microbiology. At various times postinfection, mice were anesthetized with Metofane (Mallinckrodt Veterinary, Inc., Mundelein, Ill.), and blood was withdrawn via cardiac puncture. After euthanization (via cervical dislocation), a saline lavage of the peritoneal cavity was performed by using 3 or 5 ml of sterile saline, and lavage fluid (~2 to 4 ml) was collected. Livers were excised, weighed in 10 ml of saline, and homogenized (Omni-International GLH Homogenizer, Marietta, Ga.). Blood, peritoneal lavage fluid, and homogenized livers were serially diluted and plated on TSA, and bacterial colonies were enumerated after 24 h of incubation at 37°C.

Serum IL-6 and human IgG assay. Serum was separated from the blood (obtained via cardiac puncture) by using a benchtop HN-SII centrifuge (10 min at 3,000 rpm; IEC, Needham Heights, Mass.) and assayed with a commercial ELISA ( = 450 nm; Pharmingen, Inc., San Diego, Calif.) to determine the levels of interleukin-6 (IL-6) and human IgG. The detection range for the IL-6 assay was between 15 and 2,000 pg/ml, and for the human IgG it was between 5 and 5,000 ng/ml. Standard curves were constructed from known amounts of murine IL-6 contained in the ELISA kit and from commercially pooled human IgG (lot 2620M039A, Gammagard), respectively. Murine serum IL-6 and human IgG levels were determined by comparing the experimental absorbance values from serum or peritoneal lavage to standard curves.

In vitro opsonophagocytic assay. Murine peritoneal lavage fluid, collected 2 h after bacterial challenge and human IgG treatment, was assayed to determine the opsonizing activity of the applied IgG. Fixed volumes of peritoneal fluid (2 ml in test tubes) were incubated in vitro at 37°C and agitated at 150 rpm. The bacterial burden in peritoneal lavage fluid was assayed immediately upon collection and after 2 h of incubation by plating 100 µl of serially diluted peritoneal fluid on TSA. Colonies were enumerated after 24 h of incubation at 37°C.

Statistical analysis. Data in this study are expressed as the mean ± the standard error of the mean. Student's t tests were used to compare the control and therapy groups of the bacterial burden enumeration studies, while z tests and analysis of variance (ANOVA) tests were used to compare mortality. All probabilities of less than 5% were considered significant. Datum outliers, defined as any datum outside of the range of the mean ± 2 times the standard deviation, were excluded.

	RESULTS

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Polyclonal human IgG titer determination against P. aeruginosa strains. Titers of commercial pooled human IgG were determined against three strains of P. aeruginosa by using a published ELISA method (18). Titers of 355, 501, and 398 were calculated for this IgG lot against P. aeruginosa IFO-3455, M-2, and MSRI-7072, respectively. These titers represent a significant IgG binding activity against the pathogens.

Local intraperitoneal delivery of IgG. Various doses of locally delivered IgG were tested against a lethal dose of P. aeruginosa (IFO-3455, 10⁷ CFU) in four separate experiments with CF-1 mice to determine the dose benefit range. Survival of IgG-treated groups increased from the control dose of 0.005 mg and higher in a dose-dependent manner. As shown in Fig. 1, the highest percentage of survival resulted from the highest concentration of IgG (96% with 10.0 mg) delivered directly to the peritoneal cavity. A stepwise threshold of IgG efficacy is observed over a narrow therapeutic dose range beginning at ca. 0.5 mg of IgG per mouse. All IgG doses applied intraperitoneally that were higher than this produced significant improvements in mouse survival (ANOVA with Tukey's test, P < 0.008 comparing survivals with doses of 0.5 and 10 mg). An optimal efficacious dose of 10 mg of IgG per 22- to 24-g mouse (strains CF-1, CD-1, and CFW) was chosen for the survival studies to provide the most consistent results in lower numbers of mice with less variance and greater reliability.

View larger version (12K): [in this window] [in a new window]   FIG. 1.   Dose-response curve for locally applied intra-abdominal IgG against P. aeruginosa IFO-3455. The CF-1 mouse survival (n = 10 to 25 animals/group) at day 10 postchallenge with 107 CFU injected intraperitoneally simultaneous with a separate single injected dose of IgG (0.005, 0.05, 0.2, 0.5, 1.0, 5.0, or 10 mg per animal) is shown. IgG therapy increased the percent survival in a dose-dependent manner. The data represent the mean survival of IgG-treated mice from four different experiments. The difference in survival between the 0.5- and 10-mg/animal IgG dose groups is statistically significant (ANOVA with Tukey's test; P < 0.008).

View larger version (18K): [in this window] [in a new window]   FIG. 2.   CF-1, CD-1, and CFW mouse strain survival assessed for 10 days in the peritonitis model with a single local intraperitoneal injection of 10 mg of IgG or placebo treatment (5% dextrose) against a lethal dose of 107 CFU of P. aeruginosa IFO-3455 injected intraperitoneally (n = 10 to 35 animals/group). IgG treatment resulted in significantly increasing survival compared to placebo (5% dextrose) treatment in all three mouse strains (ANOVA with Tukey's test; P < 0.001).

View larger version (27K): [in this window] [in a new window]   FIG. 3.   Pathogen strain influence on mouse survival (day 10) in a peritonitis model with local IgG administration. Three strains of P. aeruginosa were each separately injected intraperitoneally (dose = 107 CFU) simultaneously with separate, single injections of 10 mg of pooled human IgG or placebo (5% dextrose) (n = 10 animals/group). IgG treatment significantly increased the survival rates compared to the placebo treatment (z test; P < 0.05).

Efficacy of local IgG application pre- and postchallenge. To investigate the prophylactic and therapeutic properties of locally applied IgG, 10-mg IgG doses were delivered intraperitoneally in CF-1 mice (i) 1, 3, and 6 h before; (ii) at the time of; and (iii) 1, 3, 6, 12, and 18 h after bacterial challenge (IFO-3455, 10⁷ CFU). Figure 4 shows the results for these studies. IgG administered 1, 3, and 6 h prior to bacterial challenge and simultaneously with bacterial challenge produced 100% survival (P < 0.05 compared to the placebo-treated group). Mice treated with locally injected IgG 1, 3, 6, and 12 h after bacterial challenge exhibited significantly higher survival rates compared to the placebo-treated group (P < 0.05), whereas mice treated at 18 h postchallenge showed no significant differences in survival.

View larger version (38K): [in this window] [in a new window]   FIG. 4.   Survival in the mouse peritonitis model (day 10) influenced by time of local IgG administration relative to bacterial challenge. Single IgG injections intraperitoneally (10 mg) were administered prior to (prophylaxis), simultaneously with (challenge), or after (therapy) lethal intraperitoneal injections of P. aeruginosa IFO-3455 (107 CFU, n = 10 to 25 animals/group). All IgG-treated groups marked with an asterisk showed significantly increased survival rates compared to the placebo (5% dextrose) treatment group (z test and ANOVA with Tukey's test; P < 0.05).

Systemic and local IgG in vivo distribution over time. Serum and peritoneal lavage fluid were collected from groups of CF-1 mice treated with 10.0 mg of IgG and euthanized at 0, 2, 3, 6, 9, 12, 24, 36, and 48 h and every 24 h thereafter up to day 7 after intraperitoneal challenge with IFO-3455 to compare the systemic and local distributions of human IgG. Placebo (5% dextrose)-treated mice were only analyzed at 0, 2, and 3 h, and no human IgG was detectable (data not shown). As shown in Fig. 5, the amounts of intraperitoneally resident human IgG decline sharply by between 2 and 3 h postadministration (half-life, ~2.5 h) and decrease constantly over time. Simultaneously, human IgG levels in serum increase as peritoneal IgG decreases, spiking to almost 3 mg/ml at 9 h and decreasing thereafter. Human IgG is detectable rapidly in serum after intraperitoneal administration and remains detectable by ELISA methods in both serum and peritoneal lavage for up to 7 days postchallenge.

View larger version (23K): [in this window] [in a new window]   FIG. 5.   ELISA detection of human IgG levels in murine serum () and peritoneal lavage fluid () after bacterial challenge following intraperitoneal injection of IgG and intraperitoneal lethal injections of P. aeruginosa IFO-3455 (107 CFU, n = 3 or 4 animals per time point in each group) for 7 days. Human IgG is detectable rapidly in mouse serum after intraperitoneal administration and remains detectable by ELISA methods in both serum and mouse peritoneal lavage fluid for up to 7 days. (Inset) Human IgG levels in mouse serum and peritoneal lavage fluid in the first 12 h postadministration.

Quantification of bacteria in systemic tissues and IL-6 levels in serum. Tissue samples were collected from groups of CF-1 mice treated with 1.0 mg of IgG or placebo (0.2 M glycine) 6, 24, and 72 h after intraperitoneal challenge with IFO-3455 in order to compare the bacterial burdens in the liver, peritoneal cavity, and blood. A lower, nonlethal 10⁶ CFU challenge was used to ensure animal survival up to the 72-h time point. Liver, blood, and peritoneal lavage fluid samples from placebo-treated control mice and local IgG-treated mice were homogenized, serially diluted, and plated, and the values for log CFU per tissue were compared. The results (Fig. 6) show that IgG-treated mice have significantly reduced numbers of bacteria in the liver, blood, and peritoneal lavage fluid 6 h postchallenge compared to the bacterial burden in control mice (P < 0.05). Bacteria were not present in the liver, peritoneal lavage fluid or blood of IgG-treated mice by 24 h postchallenge. Additionally, ELISA was used to determine the murine serum levels of the inflammatory cytokine IL-6. Figure 7 shows that IgG-treated mice had significantly lower levels of IL-6 by 6 h postchallenge compared to the control groups (P < 0.05). The low IL-6 levels at 24 and 72 h post-bacterial challenge were comparable to normal circulating murine IL-6 levels and correlated with the low bacterial burden found in the peritoneal cavity, liver, and blood (Fig. 6).

View larger version (16K): [in this window] [in a new window]   FIG. 6.   Bacterial burden at various tissue sites assessed 6 h after intraperitoneal injection of 1.0 mg of IgG against 106 CFU of P. aeruginosa IFO-3455 given intraperitoneally. Mice (n = 10) peritoneal lavage fluid (PL), liver homogenate, and blood analysis yielded CFU values that show that IgG treatment significantly decreased the bacterial burden compared to the placebo treatment (0.2 M glycine) after 6 h in all samples (t test; P < 0.05). The PL and blood bar graphs represent the log10 CFU/milliliter, and the liver bar graph shows the log10 CFU/gram of liver.

View larger version (24K): [in this window] [in a new window]   FIG. 7.   Serum IL-6 levels after intraperitoneal injection of 1.0 mg of IgG against a nonlethal intraperitoneal dose (106 CFU) of P. aeruginosa IFO-3455. Serum IL-6 levels of CF-1 mice (n = 5 to 25) were determined by ELISA. IgG treatment decreased IL-6 levels significantly compared to the control (P = 0.04) by 6 h after the bacterial challenge. A saline-plus-glycine placebo treatment without a bacterial challenge was used to determine normal background IL-6 levels in CF-1 mice. Treatment with saline plus 10 mg of IgG without a bacterial challenge shows that IL-6 levels resulting from IgG treatment alone are not significantly different from the normal background IL-6 levels (t test; P < 0.05).

In vitro opsonophagocytic assay. Murine peritoneal lavage fluid was assayed in vitro 2 h postchallenge with 10⁷ CFU of P. aeruginosa IFO-3455 to determine the opsonizing influence of applied human IgG. Peritoneal lavage fluid of mice treated with 10 mg of IgG had significantly reduced levels of bacteria compared to placebo (5% dextrose)-treated mice both immediately after lavage and 2 h later (Fig. 8). The presence of human IgG facilitated the clearance of bacteria from lavage fluid, whereas control-treated lavage fluid exhibited bacterial growth during this incubation period.

View larger version (26K): [in this window] [in a new window]   FIG. 8.   In vitro opsonophagocytic assay with mouse peritoneal lavage shows enhanced bacterial clearance with IgG. Murine peritoneal lavage fluid was assayed in vitro 2 h after intraperitoneal dosing with human IgG and intraperitoneal challenge with 107 CFU of P. aeruginosa IFO-3455. Peritoneal lavage fluid of mice treated with 10 mg of IgG significantly reduced the levels of bacteria compared to placebo (5% dextrose)-treated mice both immediately after peritoneal lavage and 2 h later (t test; P < 0.05). The presence of human IgG facilitated the clearance of bacteria from lavage fluid, whereas the control lavage fluid exhibited bacterial growth during the incubation.

	DISCUSSION

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Local delivery of IgG directly to tissue and wound surfaces represents a potential alternative strategy against infections that is both independent of antibiotic resistance and complementary to current antibiotic treatment regimens. In this study, locally delivered IgG has been assessed in a murine peritonitis model to determine its efficacy alone against P. aeruginosa. This common nosocomial pathogen (7, 24, 28, 40, 44) is responsible for 5 to 10% of CAPD-related and 24% of acute community-acquired perforating appendicitis infections (21), and it is a pathogen of particular clinical concern due to its increasingly frequent antibiotic-resistant forms that are emerging during treatment with broad-spectrum antibiotics, its late complications, and its high morbidity (21). In 1986, Lamperi and coworkers reported that the local application of pooled human IgG (SRK-Ig [Swiss Red Cross]; pooled IgG from volunteers) as an intra-abdominal dialysate lavage treatment was beneficial against certain forms of peritonitis (17, 25, 26). The current study shows that locally delivered pooled human IgG significantly increases the survival of all IgG-treated groups in a dose-dependent manner against different challenges of multiple P. aeruginosa strains and in different strains of mice compared to control treatments.

Recent studies linking the inhibition of P. aeruginosa motility and associated virulence to human pooled polyclonal IgG and its titers in vitro support a specific IgG mechanism that confers protection (37). Since all P. aeruginosa strains used here are flagellate pathogens and since commercial human polyclonal IgG is known to significantly hinder both flagellar pathogen motility in vitro (37) and infection in vivo (10), the observed efficacy of IgG against infection is attributed to these immunospecific modes of action. Treatment with HSA failed to improve survival over placebo treatment, demonstrating that local IgG efficacy is due to specific polyclonal IgG antibody interactions with P. aeruginosa and not due to nonspecific protein effects. The ELISA-based high IgG titers determined against the three P. aeruginosa strains used in this study are consistent with the observed reduction of burden and enhanced survival.

The observed success of this commercial IVIG preparation in enhancing prophylactic survival indicates that specific hyperimmune (15, 16) and monoclonal (1, 35) sera produced against gram-negative exo- and endotoxins may not be required for prophylactic efficacy. The observed decline of IgG therapeutic efficacy postinfection suggests that these alternative sera may prove useful for improving titers or efficacy for this late therapeutic condition (32). This higher survival rates of IgG groups against the lethal IFO-3455 strain in outbred cohorts of CF-1, CD-1, and CFW mice (Fig. 2), together with the significantly increased survival of IgG-treated CF-1 mice against the M-2, MSRI-7072, and IFO-3455 pathogen strains (Fig. 3), show that IgG efficacy is not strain dependent in either bacteria or mice. Differences observed in the survival of the three different mouse strains against IFO-3455 challenge (Fig. 2) are not readily explained. All strains are outbred genetically, supporting some statistical variance in their immune responses. Otherwise, all strains are white albino breeds, with the CD-1 and CFW strains originating overseas (i.e., Switzerland).

Abundant peritoneal macrophages and opsonins, including IgG and complement, are major endogenous constituents of the host's immune defense against peritoneal infection (20, 22, 23). Macrophages and neutrophils are chemotactically attracted to bacterial endotoxins and are signalled by cytokines. Therefore, the prophylactic presence of specific IgG pools should benefit the host against P. aeruginosa infections and peritonitis in general. Measurable IgG titers reflect extensive and rapid IgG binding to P. aeruginosa epitopes, limiting P. aeruginosa motility, sterically hindering peritoneal epithelial attachment, and enhancing phagocytic clearance. The data in Fig. 8 support IgG-enhanced killing in peritoneal lavage isolates as a result of increased opsonic activity and bacterial opsonization by peritoneally applied exogenous human IgG. Locally administered IgG alone confers on the mouse the ability to survive infection by otherwise-lethal bacterial challenges from the three P. aeruginosa strains.

Preventative (prophylactic) antibiotics are most effective against infection when therapeutic tissue concentrations are present at the time of bacterial contamination; antibiotic effectiveness is lost when the drug is administered 3 h after tissue pathogen contamination (41). In this study, locally applied IgG was most beneficial as a prophylaxis when given prior to and simultaneously with bacterial challenge (Fig. 4). This effect coincides with the detected rapid clearance of intraperitoneally administered IgG into the mouse's systemic circulation. That is, protection against infection appears to be a combination of IgG-mediated effects both locally and systemically. Figure 5 shows that locally delivered IgG is taken up systemically within 3 h of injection into the peritoneal cavity. This result is consistent with extensive perfusion of the peritoneum and the use of intraperitoneal injection as an established method for giving systemic anesthetics to mice. Hence, a significant fraction of human IgG given locally is rapidly systemically available. Nonetheless, data from Fig. 8 show that the fraction of human IgG still present in the peritoneal cavity maintains a substantial ability to facilitate bacterial clearance.

The proliferation of bacteria from the site of initial abdominal infection leads to the infection of other organs, the overproduction of endotoxins, the induction of cytokine cascades, the progression to septic shock, and sepsis (40). Increases in circulating levels of inflammatory cytokines, including tumor necrosis factor alpha, gamma interferon, IL-8, and IL-6 (2, 4, 21, 31, 47), are clinical indicators of peritonitis (40). Reduced circulating IL-6 correlates with decreased host microbial load. Low levels of systemic bacteria detected at 6 h (Fig. 6) and decreased IL-6 levels (Fig. 7) in locally IgG-treated groups compared to placebo-treated control groups are consistent with both local and systemic IgG opsonophagocytic activity. Opsonophagocytic data (Fig. 8) support continued bacterial clearance in peritoneal lavage fluid containing human IgG, while the bacterial burden increases in this lavage fluid without exogenous IgG. Human IgG is still detectable peritoneally for up to 7 days, with more substantial amounts circulating in blood (Fig. 5). Extrapolation of the detected peritoneal human IgG bacterial clearance activity (Fig. 8) to longer times in the presence of the remaining peritoneal human IgG (Fig. 5) supports possibly prolonged local opsonophagocytic reduction of host bacterial burden, along with systemic IgG protection to confer survival.

The data indicate that locally delivered IgG, applied most beneficially as a prophylactic measure, lowers the incidence and severity of infection by reducing the acute bacterial burden and systemically inhibiting sepsis. Because peritonitis is considered a compartmentalized inflammatory process, with much more significant cytokine production locally versus systemically, it has been suggested that anticytokine therapies would be most effectively directed locally at the peritoneal cavity (40). The use of locally administered, pooled human IgG is also complementary to current antibiotic therapies. Combined IgG-antibiotic treatments are a potentially useful extension of therapy against infection. Additionally, this strategy is an option for combating bacteria that are resistant or may develop resistance to antibiotics (6, 12, 17, 19, 43), since IgG functions independently of resistance mechanisms. As a potential clinical prophylactic, pooled human IgG might be applied prior to closure during abdominal surgery as a topical lavage, or as a treatment in CAPD dialysate fluid, by using targeted delivery vehicles or controlled release strategies (e.g., microspheres, gels, or coatings). Tailored optimization of IgG local dose and delivery kinetics is an anti-infective strategy that is different from the use of IVIG. Such an alternative approach could be suitable for a variety of infectious complications and clinical needs beyond the scope of peritonitis. Such approaches offer new possibilities for decreasing the risks of postsurgical infection and associated morbidity and for lowering overall mortality rates.