Susceptibility of burned mice to Pseudomonas aeruginosa and protection by vaccination

Early infection during burn-induced inflammatory response results in increased mortality and p38-mediated neutrophil dysfunction

Following burn injury, the host is susceptible to bacterial infections normally cleared by healthy patients. We hypothesized that during the systemic immune response that follows scald injury, the host's altered immune status increases infection susceptibility. Using a murine model of scald injury under inhaled anesthesia followed by intraperitoneal infection, we observed increased neutrophil numbers and function at postburn day (PBD) 1 compared with sham-burned and PBD4 mice. Further, increased mortality, bacteremia, and serum IL-6 were observed in PBD1 mice after Pseudomonas aeruginosa (PA) infection compared with sham-burned and PBD4 mice infected with PA. To examine these disparate responses, we investigated neutrophils isolated at 5 and 24 h following PA infection from PBD1 and sham-burned mice. Five hours after infection, there was no significant difference in number of recruited neutrophils; however, neutrophils from injured mice had decreased activation, active-p38, and oxidative burst compared with sham-burned mice. In direct contrast, 24 h after infection, we observed increased numbers, active-p38, and oxidative burst of neutrophils from PBD1 mice. Finally, we demonstrated that in neutrophils isolated from PBD1 mice, the observed increase in oxidative burst was p38 dependent. Altogether, neutrophil activation and function from thermally injured mice are initially delayed and later exacerbated by a p38-dependent mechanism. This mechanism is likely key to the observed increase in bacterial load and mortality of PBD1 mice infected with PA.

Pseudomonas immunotherapy: a historical overview

The historic development of vaccines to be used as immunotherapy for Pseudomonas aeruginosa infections, in various patient populations, is reviewed. Commentary is offered concerning the relevance of each approach in light of our current understanding of the pathological process of these infections.

Efeito imunomodulador de hormônios tímicos sobre o trauma térmico experimental

O trauma grave, em particular térmico, promove a imunodepressão. Hormônios tímicos podem modificar a resposta imune nesta comdição. O objetivo desta pesquisa foi investigar o efeito imunomodulador do hormônio tímico timoestimulina sobre a imunidade celular em trauma térmico, traduzida pela resposta dos testes cutâneos de hipersensibilidade tardia. Na primeira etapa do experimento, ratos Wistar foram sensibilizados com KHL e posteriormente submetidos ao teste cutâneo de hipersensibilidade tardia (TCHT). Dez animais com resposta positiva foram submetidos a queimadura cutânea padronizada. Testes cutâneos seqüenciais revelaram significativa anergia cutânea no 21º e 30º dias pós-queimadura e interrupção do ganho de peso. Na etapa seguinte, ratos previamente sensibilizados e com resposta positiva ao TCHT, foram divididos nos grupos TAQ (seis ratos) tratados com timoestimulina, por via intramuscular, na dose de 0,25 mg, antes e após queimadura, grupo TDQ (seis ratos) tratados com a mesma dose de timoestimulina apenas após a queimadura e grupo CSQ (cinco ratos) tratados com solução salina, im, após a queimadura. Ocorreu aumento significativo do peso corpóreo e da resposta do TCHT a partir de duas semanas pós queimadura nos grupos TAQ e TDQ. Nas condições da presente pesquisa, timoestimulina misnistrada antes e após a queimadura experimental associa-se a melhora da resposta ao teste cutâneo de hipersensibilidade tardia e ganho de peso corpóreo.

Genetics of natural resistance to thermal injury

The possible influence of genetic factors in conditioning the host's natural resistance to the lethal effects of severe thermal injury has been studied in 908 rats of comparable age and weight, originating from two outbred, eight inbred, and two congenic strains of animals of defined genetic background. Each animal was exposed to a standard, full-thickness, 40% body surface area skin burn by controlled contact with a heated metal plate. The 21-day postburn mortality was 100% in 217 Fisher (F-344) and 97 ACI male and female rats. The mortality was reduced to 49-63% in an intermediate group of 84 Lewis, 98 Wistar, 48 Sprague-Dawley, 96 Wistar-Furth (WF), and 48 Osborne-Mendel (OM) male rats; 48 female OM rats had a mortality of 86% at 21 days after injury. The same injury produced a mortality in 4% in 90 Buffalo (BUF) and 22% in 41 Brown-Norwegian (BN) males, while females of the same strains exhibited a 21-day mortality of 23% and 54%, respectively. Further studies of the effects of similar injury in two congenic strains of rats derived from some of the inbred lines of animals listed above yielded a 21-day mortality of 50% in 18 BN.1B(BUF) and 20% in 15 BN.1U(WF) male rats, and 65% and 36%, respectively, in females of the same lines. These data point to the importance of genetic factors as a key determinant of host resistance or susceptibility to the effects of severe thermal injury. The segregation of responses to thermal injury in inbred rats into susceptible, intermediate, and resistant groups on the basis of strain origin indicates that such natural resistance may be a quantitative trait. One of the genetic components affecting host resistance is sex-linked. The existence of genetically controlled variations in natural resistance to trauma may be an important determinant of survival and may be a source of guidelines for the triage and clinical care of injured patients. It may also be an important selective factor in evolution.

Protective immunity induced in mice by immunization with high-molecular-weight polysaccharide from Pseudomonas aeruginosa

A high-molecular-weight alkali-labile polysaccharide (PS) isolated from the slime of immunotype 1 Pseudomonas aeruginosa was tested for its ability to protect mice from lethal challenge with the live, homologous organism. Intraperitoneal (i.p.) injection of 10 to 25 microgram of the PS protected 60 to 70% of the mice against challenge with up to 50 50% lethal dose units. Although single immunization of mice with up to 250 microgram of PS effected protective levels of only 70%, two successive immunizations provided 100% protection. Subcutaneous and intravenous immunization with PS also provided protection to i.p. challenges with immunotype 1 P. aeruginosa, but not to i.p. challenge with immunotype 4 P. aeruginosa. Although lipopolysaccharide (LPS) was found to be more immunogenic than PS in out studies, contamination of the alkali-labile PS with LPS did not account for the protection seen. Alkali treatment (0.1 N NaOH, 37 degrees C, 2 h) of the PS destroyed its protective effectiveness, while similarly treated LPS retained its capacity for inducing immunity in mice. Adsorption and passive protection studies with sera raised to either PS or a mixture of PS and LPS indicated that antibody directed to the alkali-labile PS antigen was capable of contributing to the protection of mice against challenge with P. aeruginosa.

Kinetics of humoral responsiveness in severe thermal injury

Severe thermal injury has the capacity to increase the rate of generation of antibody-forming cells in mice. The intensity of stimulation appears to be proportional to the extent of injury. The effect has been observed in animals burned within 1 hr before or after sensitization with test antigen(s), and persists up to 14 days after injury. Thereafter, the stimulatory effect wanes, and disappears by the 21st day after burning. Responses to T-cell (thymus derived lymphocytes) dependent antigens (sheep erythrocytes; sheep erythrocytes coupled to TNP) and to antigens not requiring T and B-cell (bone marrow derived lymphocytes) cooperation (DNP-Ficoll) appear to be equally affected by thermal injury. The mechanisms underlying this form of enhanced antibody response are not clear. The data, however, support the possibility that the burn wound may release factor(s) capable of enhancing humoral responsiveness in the injured animal. Such factor(s) do not appear to be endotoxins.

Selective effects of thermal injury on mouse peritoneal macrophages

Normal mice or mice burned 6 days previously were injected intraperitoneally with either saline or 50 mug of concanavalin A. Four days after the injection the peritoneal macrophages were collected and examined in vitro. Macrophages from concanavalin A-injected mice appeared activated because several in vitro parameters of activity were increased. Examination of macrophages from burned animals revealed a selective depression of macrophage activity.

Vascular permeability factor of Pseudomonas aeruginosa

The production of vascular permeability factor (PF) by certain strains of Pseudomonas aeruginosa has been demonstrated in rabbits injected intradermally with culture filtrates followed by intravenous injection with Pontamine Sky Blue 6BX. The dose-response curve was found to be rectilinear when lesion diameters, within the range of 10 to 20 mm, were plotted against log dose. Thus, PF in test filtrates can be measured with reasonable accuracy by the concomitant testing of a reference PF. In contrast to the titers of PF obtained with Vibrio cholerae cultures, those with strains of P. aeruginosa were rather low. Thus far, PF has been demonstrated only in shallow still cultures of P. aeruginosa and not in shake cultures. A variety of commercial media were tested for the production of PF, but none was satisfactory. A synthetic medium that gave more reproducible and higher yields of PF was developed. Cultivation at 30 C generally gave higher yields of PF than at 37 C. PF was destroyed by heating at 60 C for 30 min or by digesting with trypsin or Pronase. Strains producing larger amounts of PF appeared to have greater virulence when inoculated onto the surface of burns in mice than those yielding little or no PF.

Early protection by vaccines in burns

Groups of mice, inoculated once a week for 3 weeks with vaccines from culture filtrates of Pseudomonas aeruginosa and Proteus mirabilis and slime from Klebsiella aerogenes, were protected against lethal infections with the homologous strains injected intraperitoneally after burning.

A single injection of pseudomonas and proteus vaccines also protected burned and unburned mice against lethal, homologous, i.p. infections as early as 24-48 hr after vaccination. The klebsiella vaccine did not induce early protection. A single injection of a trivalent vaccine, made by combining pseudomonas, proteus and klebsiella vaccines in equal proportions, protected burned mice against lethal K. aerogenes, Ps. aeruginosa and Pr. mirabilis infections.

Mice which were protected against homologous infections had no detectable agglutinins in their sera until three days after the protective response had been demonstrated.

Passive Immunization Against Experimental Pseudomonas Infection: Correlation of Protection to Verder and Evans “O” Serotypes

Passive-protection tests were conducted in mice with antisera from rabbits immunized with formalinized or heat-killed cells or with an alcohol-precipitated fraction from the slime layer. Protection was conferred by antisera against the heatstable antigens and correlated well with agglutinin levels. Specificity was found to relate closely to the heat-stable “O” serotypes as defined by Verder and Evans.

Immunization of mice and chinchillas against Pseudomonas aeruginosa

The possibility of production of an effective vaccine against Pseudomonas aeruginosa infections in fur-bearing animals was investigated. Twenty-three strains of Pseudomonas aeruginosa isolated from diseased chinchillas and mink were tested in mice for their immunogenic properties. Nineteen of these strains produced good immunity against homologous strains, and three of these produced also good immunity against heterologous strains. Of the remaining four strains two produced moderate immunity and two no immunity. It was found that 0.05% or 0.5% formalin added to suspensions of Pseudomonas aeruginosa or ultrasonification of the suspension produced better results than 0.5% phenol, 0.3% alcohol or heat at 100 degrees C for half an hour. Chinchillas vaccinated with two doses of formolized Pseudomonas aeruginosa bacterins were immune for 36 weeks after the second dose, while all controls died within 48 hours after being challenged. It was found that the protection afforded by the polyvalent bacterin extended beyond the strains included in the vaccine.A field survey on 34 ranches which included over 7,700 chinchillas showed very promising and encouraging results.

Protection by vaccination against Pseudomonas infection after thermal injury

Active immunization is effective in the prophylaxis of Pseudomonas septicemia in burned mice. Vaccines were prepared from bacterial cells and growth medium of Verder's 10 different O serological types of Pseudomonas aeruginosa strains, as well as from Escherichia coli and Proteus mirabilis. Mice given a tail burn could be significantly protected against a local Pseudomonas challenge by both specific and, to a lesser extent, by nonspecific Pseudomonas vaccines prepared either from bacterial cells or from the medium in which they were grown. The vaccine was effective when administered prior to or after thermal trauma. After a more extensive rump burn, the protective effect of a specific vaccine given after thermal injury was significant only when the challenge was postponed until 4 days postburn; the level of protection was less than in the mice with smaller burns.