Age-related differences in the neutrophil response to pulmonary pseudomonas infection.

BACKGROUND: Pseudomonas aeruginosa pneumonia is more common and more lethal in the elderly. The immunologic underpinnings of this increased incidence and mortality have not been evaluated, however are assumed to be a complication of age-associated immune dysfunction. METHODS: Young (10-12week old) and aged (18-20month old) BALB/c mice were subjected to intratracheal infection of P. aeruginosa. Animals were sacrificed 24h after inoculation. The lungs were collected for analysis of lung pathology, chemokine levels, neutrophil counts, and myeloperoxidase activity. RESULTS: Pulmonary levels of the neutrophil chemokine KC are significantly higher in aged mice relative to young following P. aeruginosa infection. Despite this, neutrophil counts are higher in young mice compared to aged mice after infection. Furthermore, the neutrophils are predominantly found in the air space of young infected mice. This correlated with increased myeloperoxidase activity from bronchoalveolar lavage specimens of young mice relative to aged mice after infection. CONCLUSIONS: Neutrophil migration into the lungs is impaired in aged mice 24h after intratracheal infection despite elevated chemokine levels, suggesting that immunosenescence is impairing neutrophil migration.

Combined radiation and burn injury results in exaggerated early pulmonary inflammation.

Events such as a nuclear meltdown accident or nuclear attack have potential for severe radiation injuries. Radiation injury frequently occurs in combination with other forms of trauma, most often burns. Thus far, combined injury studies have focused mainly on skin wound healing and damage to the gut. Since both radiation exposure and remote burn have pulmonary consequences, we examined the early effects of combined injury on the lung. C57BL/6 male mice were irradiated with 5 Gy of total body irradiation followed by a 15% total body surface area scald burn. Lungs from surviving animals were examined for evidence of inflammation and pneumonitis. At 48 h post-injury, pathology of the lungs from combined injury mice showed greater inflammation compared to all other treatment groups, with marked red blood cell and leukocyte congestion of the pulmonary vasculature. There was excessive leukocyte accumulation, primarily neutrophils, in the vasculature and interstitium, with occasional cells in the alveolar space. At 24 and 48 h post-injury, myeloperoxidase levels in lungs of combined injury mice were elevated compared to all other treatment groups (P < 0.01), confirming histological evidence of neutrophil accumulation. Pulmonary levels of the neutrophil chemoattractant KC (CXCL1) were 3 times above that of either injury alone (P < 0.05). Further, monocyte chemotactic protein-1 (MCP-1, CCL2) was increased two- and threefold compared to burn injury or radiation injury, respectively (P < 0.05). Together, these data suggest that combined radiation and burn injury augments early pulmonary congestion and inflammation. Currently, countermeasures for this unique type of injury are extremely limited. Further research is needed to elucidate the mechanisms behind the synergistic effects of combined injury in order to develop appropriate treatments.

Advanced age impairs macrophage polarization.

Aging affects many aspects of the cellular function of macrophages. Macrophages play a critical role in innate immunity, acting as sentinels to fight pathogens, promoting wound healing, and orchestrating the development of the specific acquired immune response. However, little is known about how age influences the ability of macrophage to change phenotypes in response to environmental factors. This study examined the age-associated defects on macrophage polarization toward a pro-inflammatory (M1) or an anti-inflammatory (M2) phenotype. Adherent splenocytes enriched for macrophages were cultured with or without lipopolysaccharide (LPS), a combination of interferon (IFN)-γ and tumor necrosis factor (TNF)-α or interleukin (IL)-4. A panel of M1 markers, inducible nitric oxide synthase (iNOS), IL-6, IL-1ß, and TNF-α, and M2 markers, including arginase-1 (Arg1), Ym1, and Found In Inflammatory Zone 1 (FIZZ1), were analyzed. IL-6 mRNA in cells from aged mice was decreased by 78% and 58% compared with young after stimulation with LPS or IFN-γ and TNF-α (P<0.05), respectively. Also, there was a marked reduction in the induced levels of iNOS, IL-1ß, and TNF-α in cells from aged mice relative to young controls. Similarly, IL-4 exposure resulted in a reduction of M2 markers in adherent splenocytes from aged mice compared with younger animals. This was consistent with a 28% decrease in splenic F4/80(+)IL-4R(+) cells in aged mice relative to controls, although IL-4R expression on these cells did not vary between age groups. In contrast, levels of M1 and most M2 markers, save for FIZZ1, in bone marrow-derived macrophages were similar between the age groups, irrespective of stimuli. These data imply that impaired macrophage polarization in the elderly may dysregulate the development of the host response, making them more susceptible to infectious diseases and that the aging microenvironment may be a key modulator of these macrophage-elicited responses.

Development of a combined radiation and burn injury model.

Combined radiation and burn injuries are likely to occur after nuclear events, such as a meltdown accident at a nuclear energy plant or a nuclear attack. Little is known about the mechanisms by which combined injuries result in higher mortality than by either insult alone, and few animal models exist for combined radiation and burn injury. Herein, the authors developed a murine model of radiation and scald burn injury. Mice were given a single dose of 0, 2, 4, 5, 6, or 9 Gray (Gy) alone, followed by a 15% TBSA scald burn. All mice receiving ≤4 Gy of radiation with burn survived combined injury. Higher doses of radiation (5, 6, and 9 Gy) followed by scald injury had a dose-dependent increase in mortality (34, 67, and 100%, respectively). Five Gy was determined to be the ideal dose to use in conjunction with burn injury for this model. There was a decrease in circulating white blood cells in burn, irradiated, and combined injury (5 Gy and burn) mice by 48 hours postinjury compared with sham (49.7, 11.6, and 57.3%, respectively). Circulating interleukin-6 and tumor necrosis factor-α were increased in combined injury at 48 hours postinjury compared with all other treatment groups. Prolonged overproduction of proinflammatory cytokines could contribute to subsequent organ damage. Decreased leukocytes might exacerbate immune impairment and susceptibility to infections. Future studies will determine whether there are long lasting consequences of this early proinflammatory response and extended decrease in leukocytes.