Mice Survival and Plasmatic Cytokine Secretion in a “Two Hit” Model of Sepsis Depend on Intratracheal Pseudomonas Aeruginosa Bacterial Load

Abstract

Sepsis is characterized by pro- and anti-inflammatory responses following infection. While inflammation is responsible for widespread organ damage, anti-inflammatory mediators lead to immunoparalysis increasing susceptibility to secondary infections (nosocomial pneumonia). We aimed to investigate the impact of bacterial load on survival and cytokine release in a two-hit murine (C57BL/6J) model of CLP followed by P. aeruginosa pneumonia. Plasmatic TNFα, IL-6, IL-10, sTNFr I and II were quantified until 13 days. At D5, splenocytes were processed for immunological assays or mice were intratracheally instilled with Pseudomonas aeruginosa (5.106, 2.107 and 108 CFU) to evaluate survival and cytokines production. TNFα, sTNFrs, IL-6 and IL-10 increased 2h post CLP. TNFα and sTNFrs declined respectively one and two days later. In CLP mice, IL-6 and IL-10 remained high for the whole experiment, as compared to Sham. At D5, for CLP mice, whereas total T cells population (CD3+) decreased, Treg fraction (CD4+/CD25+) increased. In parallel, T cells proliferation and LPS-stimulated splenocytes ability to release TNFα decreased. At D13, survival was 100% after 5.106 CFU, 50% for CLP mice after 2.107 CFU and 0% for CLP and Sham after 108 CFU. After instillation, IL-10 and IL-6 increased and appeared to be dose and time dependent. Pseudomonas was detected in all CLP and Sham’s lungs; in spleen and liver only in CLP at 2.107 CFU, and in CLP and Sham at 108 CFU. We demonstrated that post-CLP immunosuppression followed by Pseudomonas aeruginosa lung instillation increases mortality reactivates cytokines secretion and is associated with systemic dissemination in septic mice depending on bacterial load.

Whatever happened to the Shwartzman phenomenon?

“…The dermal or generalized Shwartzman-like reaction ("two hit" model) [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][56][57][58][65][66][67][68] Endotoxin tolerance (LPS reprogramming) [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][56][57][58][65][66][67][68] Overall primary mode of transmission would be an instant, international folk hero indeed. Many theories were postulated to explain the cause of the illness ranging from bad water, miasma theory (airborne mists and contaminated, dirty, living conditions), fomites (particularly bed cloths and linens) mosquitos, fungi, bacteria, or tiny filterable agents.…”

“…A summary of the advances in understanding the interactions between the coagulation system and innate immunity, differences between endotoxin priming and endotoxin tolerance are listed in Table 1. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][65][66][67] Univisceral Shwartzman-like reaction Local Shwartzman reaction can be induced many different tissues and is not limited to the skin. 68,69 The reaction can be induced in the lung by repetitive intratracheal administration of an inoculum.…”

Interleukin-1 receptor-associated kinase 3 downregulation in peripheral blood mononuclear cells attenuates immunosuppression in sepsis

“…Numerous studies have investigated T cell function in sepsis, and propose that apoptosis, cellular exhaustion, impaired responsiveness to stimuli and impaired cytokine responses are primarily involved (18,21,22). In addition, previous studies have demonstrated that IL-7 treatment induces T cell proliferation and decreases lymphocyte apoptosis, thus improving the prognosis of patients diagnosed with sepsis (23)(24)(25)(26).…”

Pituitary Adenylate Cyclase-Activating Polypeptide Prevents Mortality Caused by Septic Peritonitis in Mice

“…Peripheral whole blood and peritoneal lavage collection were performed using aseptic technique (18). Serial dilutions were plated onto tryptic soy agar prepoured petri dishes supplemented with 5% sheep's blood (Hardy Diagnostics) and incubated aerobically overnight at 37°C.…”