A significant correlation (data not shown) was observed between the PEK values and the peritoneal CFU. == Physique 4. bacterial counts 24 hr post sepsis compared to those predicted to live (Live-P) with a PEK>16. Mice with PEK<14 were 3.1 times more likely to die compared to the PEK>16 group. To understand the mechanism of defense conferred by the pre-existing antibodies, binding of IgM or IgG to enteric bacteria was documented by flow cytometry. To determine the relative contribution of IgM or IgG, the immunoglobulins were specifically immuno-depleted from the nave plasma samples and the PEK of the depleted plasma measured. Compared to nave plasma, depletion of IgM had no effect on the PEK. However, depletion of IgG increased PEK suggesting that an inhibitory IgG binds to antigenic sites on bacteria preventing optimal opsonization of the bacteria. These data demonstrate that prior to CLP; circulating inhibitory IgG antibodies exist that prevent bacterial killing by PMNs in a CLP model of sepsis. == Introduction == In the United States, sepsis is the second-leading cause of death in non-coronary ICU patients, and the tenth-most common cause of death overall; according to data from the Centers for Disease Control and Prevention. Sepsis is usually common and also more dangerous in elderly, immunocompromised, and critically ill patients. It occurs in 12% of all hospitalizations and accounts for as much as 25% of intensive-care unit (ICU) bed utilization (1) (2). It is a major cause of death in ICUs worldwide, with mortality rates that range from 20% for sepsis to 40% for severe sepsis to >60% for septic shock (24). There are approximately 750, 000 new sepsis cases each year, with at least 210,000 fatalities (5). The economic burden for the medical care has been estimated at 16.7 billion dollars annually (5) and is increasing. As medicine becomes more aggressive, with CNX-774 invasive procedures and immunosuppression; the incidence of sepsis is likely to continue to increase (3). The National Center for Health Statistics stated that from 2000 to 2007, the rate of hospitalization for septicemia or sepsis for persons aged 6574 years increased 57%, from 6.5 per 1,000 to 10.2 indicating that there has not been much progress achieved in the treatment of sepsis (6). Though Gram unfavorable bacteria were initially thought to be the predominant organism responsible CNX-774 for sepsis (7), current studies increasingly indicate Rabbit Polyclonal to Smad1 that Gram positive bacteria and fungal organisms are also common causes of sepsis (8). Acute respiratory failure, shock, acute renal failure, coagulopathy and multiple organ failure are some of the causes of mortality in septic patients (8,9). The cecal ligation and puncture (CLP) model of sepsis induces bacterial peritonitis thereby reproducing the complex immune response of sepsis comparable to that with patients in ICU (10). In the murine model of sepsis, the first 5 days following CLP is defined as the acute phase while day 628 is defined as the chronic phase of sepsis in CNX-774 our laboratory (11). Mice which die during the early or acute phase of sepsis have an increase in body weight as well as increased plasma IL-6 levels indicating activation of the immune system (12). Both pro-inflammatory and anti-inflammatory cytokines have been shown to be elevated during this early or acute phase (13) and chronic sepsis is also characterized by an individualized inflammatory response (14). Neutrophil recruitment to the site of infection serves as a critical immune response for host survival (15). It may be argued that septic patients die as a result of immunosuppression and failure to control bacterial growth rather than immunostimulation. This leads to the crucial question of understanding the mechanism for bacterial killing during the septic response. An inadequate host immune system that results in poor bacterial killing would represent a completely different mechanism of death compared to excessive inflammation. The present study attempts to decipher the mechanism by which some individuals die as well as others live while combating the same bacterial infection. We hypothesize that those mice that survive cecal ligation and puncture induced sepsis have pre-existing antibodies which opsonize and kill bacteria more efficiently. == Methods == == Animals == Adult female ICR mice (from Harlan-Sprague Dawley, Inc., Indianapolis, IN) were used. Mice were acclimatized to our housing room for at least 5 days before surgery. This was a temperature controlled room with 12 hours light- 12 hours dark diurnal cycle. They were provided food and waterad libitumfor the entire duration of the experiment. The experiments were approved by Boston University Animal Care and Use Committee. ==.