Thermal injury induces impaired function in polymorphonuclear neutrophil granulocytes and reduced control of burn wound infection

Abstract

Severe thermal injury induces immunosuppression, involving all parts of the immune system, especially when large fractions of the total body surface area are affected. An animal model was established to characterize the burn-induced immunosuppression. In our novel mouse model a 6% third-degree burn injury was induced in mice with a hot-air blower. The third-degree burn was confirmed histologically. The mice were allocated into five groups: control, shave, burn, infection and burn infection group. At 48 h, a decline in the concentration of peripheral blood leucocytes was observed in the group of mice with burn wound. The reduction was ascribed to the decline in concentration of polymorphonuclear neutrophil leucocytes and monocytes. When infecting the skin with Pseudomonas aeruginosa, a dissemination of bacteria was observed only in the burn wound group. Histological characterization of the skin showed a more polymorphonuclear neutrophil granulocytes (PMNs)-dominated inflammation in the group of mice with infected burn wound compared with the with burn wound group. In contrast, a higher degree of inflammation was observed in the burn wound group compared with the group of mice with infected burn wound. Furthermore, the oxidative burst and the phagocytic capacity of the PMNs were reduced in the group of mice with burn wound. Using this novel mouse model of thermal injury a decline of peripheral leucocytes was observed, whereas the increased local inflammatory response at the site of infection showed reduced capacity to contain and eliminate the infection.

Fig. 1

(a) The number of leucocytes in peripheral blood from C3H/HeN mice in the burn group (BG) compared with the shave group (SG) during 72 h. An unpaired t-test was used for statistical analysis. Each circle/square represents one mouse. (b) The number of polymorphonuclear neutrophil granulocytes (PMNs) in peripheral blood from C3H/HeN mice in the BG compared with the SG during 72 h. An unpaired t-test was used for statistical analysis. Each circle/square represents one mouse. (c) The number of monocytes in peripheral blood from C3H/HeN mice in the BG compared with the SG during 72 h. An unpaired t-test was used for statistical analysis. Each circle/square represents one mouse.

Fig. 2

(a) Culture from beneath the skin of C3H/HeN mice in the burn infection group (BIG) compared with the infection group (IG), when infected with Pseudomonas aeruginosa beneath the skin; +/- indicates the presence or absence of P. aeruginosa beneath the skin. The samples were obtained 72 h after induction of the burn wound and 24 h after the infection. (b) Blood culture from C3H/HeN mice in the BIG compared with the IG, when infected with P. aeruginosa beneath the skin; +/- indicates the presence or absence of P. aeruginosa in the blood. The samples were obtained 72 h after induction of the burn wound and 24 h after the infection. (c) Culture of liver and spleen from C3H/HeN mice in the BIG compared with the IG, when infected with P. aeruginosa beneath the skin; +/- indicates the presence or absence of P. aeruginosa in liver or spleen. The samples were obtained 72 h after induction of the burn wound and 24 h after the infection.

Fig. 3

(a,b) The number of leucocytes (a) and polymorphonuclear neutrophil granulocytes (PMNs) (b) in peripheral blood from C3H/HeN mice at five different settings. An unpaired t-test was used for statistical analysis. Each circle/square/triangle represents one mouse.

Fig. 4

(a) Oxidative burst in polymorphonuclear neutrophil granulocytes (PMNs) at 48 h post-burn from from C3H/HeN mice in the burn group (BG) compared with mice in the shave group (SG). Each circle/square represents one mouse. (b) Phagocytic capacity in PMNs at 48 h post-burn from C3H/HeN mice in the BG compared with mice in the SG. Each circle/square represents one mouse.