Cytokine administration alters the distribution of activated lymphocytes to the lung

Targeting tumour necrosis factor to ameliorate viral pneumonia

Pneumonia is a serious complication associated with inflammation of the lungs due to infection with viral pathogens. Seasonal and pandemic influenza viruses, variola virus (agent of smallpox) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; agent of COVID-19) are some leading examples. Viral pneumonia is triggered by excessive inflammation associated with dysregulated cytokine production, termed 'cytokine storm'. Several cytokines have been implicated but tumour necrosis factor (TNF) plays a critical role in driving lung inflammation, severe lung pathology and death. Despite this, the exact role TNF plays in the aetiology and pathogenesis of virus infection-induced respiratory complications is not well understood. In this review, we discuss the pathological and immunomodulatory roles of TNF in contributing to immunopathology and resolution of lung inflammation, respectively, in mouse models of influenza- and smallpox (mousepox)-induced pneumonia. We review studies that have investigated dampening of inflammation on the outcome of severe influenza and orthopoxvirus infections. Most studies on the influenza model have evaluated the efficacy of treatment with anti-inflammatory drugs, including anti-TNF agents, in animal models on the day of viral infection. We question the merits of those studies as they are not transferable to the clinic given that individuals generally present at a hospital only after the onset of disease symptoms and not on the day of infection. We propose that research should be directed at determining whether dampening lung inflammation after the onset of disease symptoms will reduce morbidity and mortality. Such a treatment strategy will be more relevant clinically.

Trauma and inflammation modulate lymphocyte localization in vivo: quantitation of tissue entry and retention using indium-111-labeled lymphocytes

OBJECTIVE

Determine the in vivo localization pattern of indium-111-labeled lymphocytes after a standardized extremity injury or standardized laparotomy and after sterile inflammation of the central nervous system.

DESIGN

Prospective animal study with concurrent controls.

SETTING

Animal research laboratory.

SUBJECTS

Male Lewis rats weighing 150-175 g.

INTERVENTIONS

Indium-111-labeled splenic lymphocytes were injected into animals after a standardized hind limb trauma or laparotomy and after induction of sterile central nervous system inflammation.

MEASUREMENTS AND MAIN RESULTS

Lymphoid and non-lymphoid organs were removed at fixed intervals after lymphocyte injection and the proportion of injected lymphocytes/gram of tissue was determined using a quantitative radionuclide calculation. Results from treated animals were compared with results from untreated control animals. Muscle injury caused early localization of lymphocytes to injured hind limbs, liver, and spleen compared with controls, whereas laparotomy decreased lymphocyte localization in the thymus and colon. Encephalitis increased localization to the central nervous system with no effect on other tissues.

CONCLUSIONS

These results identify a sensitive method to track in vivo leukocyte localization and specifically demonstrate that lymphocyte localization is altered in both traumatic and nontraumatic models of inflammation.