Influenza Virus-Specific Cytotoxic T-Lymphocyte Activity in Fischer 344 Rat Lungs as a Method to Assess Pulmonary Immunocompetence: Effect of Phosgene Inhalation

Evaluation of Cell-Mediated Immune Function Using the Cytotoxic T-Lymphocyte Assay

Evaluation of cell-mediated immunity (CMI) is a significant component in any assessment designed to predict the full range of potential immunotoxic risk underlying health risks. Among measures of CMI, the cytotoxic T-lymphocyte (CTL) response is recognized as perhaps the most relevant functional measure that reflects cell-mediated acquired immune defense against viral infections and cancer. The CTL response against T-dependent antigens requires the cooperation of at least three different major categories of immune cells. These include professional antigen-presenting cells (e.g., dendritic cells), CD4⁺ T helper lymphocytes, and CD8⁺ T effector lymphocytes. It is also among the few functional responses dependent on and, hence, capable of evaluating effective antigen presentation via both class I and class II molecules of the major histocompatibility complex (MHC). For this reason, the CTL assay is an excellent candidate for evaluation of potential immunotoxicity. This chapter provides an example of a mouse CTL assay against influenza virus that has been utilized for this purpose.

The cytotoxic T lymphocyte assay for evaluating cell-mediated immune function

Evaluation of cell-mediated immunity (CMI) is a significant component in any assessment designed to predict the full range of potential immunotoxic risk underlying health risks. Among measures of CMI, the cytotoxic T Lymphocyte (CTL) response is recognized as perhaps the most relevant functional measure that reflects cell-mediated acquired immune defense against viral infections and cancer. The CTL response against T-dependent antigens requires the cooperation of at least three different major categories of immune cells. These include professional antigen presenting cells (e.g., dendritic cells), CD4(+) T helper lymphocytes, and CD8(+) T effector lymphocytes. It is also among the few functional responses dependent on and, hence, capable of evaluating effective antigen presentation via both class I and class II molecules of the major histocompatibility complex (MHC). For this reason the CTL assay is an excellent candidate for evaluation of potential immunotoxicity. This chapter provides an example of a mouse CTL assay against influenza virus that has been utilized for this purpose.

Influenza virus host resistance model

Host resistance (HR) models are used to evaluate the effect of a test article on clearance of an infectious microorganism in order to assess total immunocompetence. HR models serve as biomarkers of net immunological health or immunological well-being. Immunotoxicity can result either in an impaired clearance of an infectious agent, increased susceptibility to an opportunistic microorganism, prevention of immunization, or exacerbation of latent viral infections. The purpose of immunotoxicity testing is to obtain data that is meaningful for safety assessment, and for immunosuppression the major objective is to determine the significance with respect to increased susceptibility to infectious disease. Host resistance models provide the only sure method of examining the influence of test articles on the functional integrity of the immune system and its ability to eliminate pathogenic microorganisms and tumor cells. They provide the means to directly assess the functional reserve of the immune system. Clearance of influenza virus requires an intact and functional immune system that incorporates a cascade of immune responses. Mechanistic studies can be included in the influenza virus host resistance model by measuring the effect of a test article on innate immunity (cytokine and interferon production, macrophage function, and natural killer (NK) cell function) and acquired or adaptive immunity (cytotoxic T lymphocyte (CTL) activity as well as influenza-specific IgM and/or IgG antibody).

Acute morphine treatment alters cellular immune function in the lungs of healthy rats

Previous work has shown that morphine suppresses the pulmonary immune response to infection and reduces pulmonary inflammation. No published studies have addressed the impact of morphine on lymphocyte function in the lungs without infection. This study addressed this question by assessing the impact of acute morphine treatment on proliferation, cytokine production, and natural killer (NK) cell activity in resident pulmonary lymphocytes from healthy rats. Male Lewis rats received either a single 15 mg/kg morphine sulfate or vehicle injection 1 h prior to sacrifice. Lungs were minced and passed through wire mesh following collagenase digestion. The resulting cell preparations were pooled (2 rats/pool) to yield sufficient cell numbers for the functional assays, and a portion of these suspensions were separated using a density gradient. Crude and purified cell suspensions were used in assays of NK cell activity and mitogen-induced proliferation and cytokine production. Morphine significantly suppressed lymphocyte proliferation and cytokine production in whole cell suspensions, but not in purified cultures. NK activity was enhanced by morphine treatment in purified treated cultures. Studies of nitrate/nitrite levels in crude and purified cultures suggest that macrophage-derived nitric oxide may be a mechanism of the suppression observed in whole cell suspensions following morphine treatment. These data are consistent with previous work showing that morphine suppresses mitogenic responsiveness and NK activity in the spleen and peripheral blood, and may do so through a macrophage-derived nitric oxide mechanism.

Morphine reduces pulmonary inflammation in response to influenza infection

The present study shows that morphine reduces the pulmonary inflammatory response to intranasal influenza virus infection in rats. Rats were infected with rat-adapted influenza virus (RAIV), which is a unique infectious agent because normal rats develop an acute pulmonary inflammatory response to RAIV and rapidly clear the virus within a few days with no mortality. Male Lewis rats were implanted with 75 mg morphine pellets or placebo pellets 72 hours prior to intranasal RAIV infection. Rats were euthanized at 2, 24, 48, 72, and 96 hours after infection. Assessment of inflammation included accumulation of inflammatory cells in the lungs, lung weight, and protein and LDH content of bronchial alveolar lavage fluid (BALF). Placebo-treated rats showed a marked inflammatory response to RAIV infection, and morphine-treated rats mounted less vigorous inflammatory responses to the infection. Taken together, these data suggest that morphine treatment impairs the inflammatory response to RAIV infection in the lungs, which is consistent with prior work demonstrating that morphine is a potent anti-inflammatory agent in other areas of the body.

Morphine alters the immune response to influenza virus infection in Lewis rats

Although the in vitro immunomodulatory effects of morphine are well-documented, few studies have explored the impact of morphine on viral infection in intact rats. We report that morphine can alter in vivo immune responsiveness to pulmonary influenza virus infection in Lewis rats. We studied rat-adapted influenza virus (RAIV) infection, which is a unique infectious disease system because normal rats develop an acute inflammatory response to RAIV in the lung, and rapidly clear the virus within a few days, with no mortality (13,20,21). Male Lewis rats were implanted with 75 mg morphine pellets or placebo pellets 72 hours prior to intranasal RAIV infection. Rats were euthanized at 2, 24, 48, 72 and 96 hours after infection and inflammation and viral load were measured in the lungs. Placebo-treated rats showed marked inflammatory responses to RAIV infection, and quickly cleared the virus from their lungs. Morphine-treated rats mounted less vigorous inflammatory responses to the infection and cleared the virus more slowly than placebo-treated rats. Although these initial data indicate that morphine can alter the response to RAIV, additional studies are necessary to fully characterize these effects.

Histopathological changes in the upper respiratory tract of F344 rats following infection with a rat-adapted influenza virus

The present study determined the morphogenesis of upper respiratory tract disease in rats following infection with a rat-adapted influenza virus. Sixty-eight 60-day-old, male F344 rats were infected by intranasal inoculation and necropsied at days 1, 2, 4, 7, 14, and 28 post-inoculation (PI). Responses to infection were studied by routine light microscopy for histopathologic changes and immunocytochemistry for localization of viral antigen. Severe infection-induced changes involved the respiratory epithelium and underlying lamina propria, and the nasal-associated lymphoid tissue, with minimal involvement of the transitional epithelium. The lesions were most severe on the septum and the medial aspect of the nasoturbinates. Viral antigen, located in the respiratory epithelium of affected regions at days 1 and 2 PI, was associated with neutrophilic infiltration and epithelial necrosis and erosion. At day 4 PI, an infiltrate of lymphocytes, macrophages, and fewer neutrophils was present, often accompanied by epithelial regeneration. Changes in the nasal-associated lymphoid tissue were evaluated using morphometric analysis and consisted of hyperplasia (days 4 to 7 PI) followed by progressive involution (days 14 to 28 PI). Mild lesions associated with foci of viral antigen were also observed in the nasal olfactory epithelium on days 1, 2, and 4 PI. The changes observed in the present study indicate the potential value of rat-adapted influenza virus infection as a model of human influenza.

Characterization of upper respiratory disease in rats following neonatal inoculation with a rat-adapted influenza virus

Neonatal F344 rats were infected with a rat-adapted influenza virus (RAIV) to use as a potential model to study the combined effects of air pollutant exposure with early life respiratory viral infections. Initially, 6-day-old pups were intranasally inoculated with RAIV or medium alone, and nasal and lower respiratory tract (LRT) tissues were assessed histologically at 1, 3, 6, and 13 days postinoculation (DPI). Immunologic assessments included thymic lymphocyte quantification and anti-RAIV immunoglobulin production. Pups then received two inoculations (at 6 and 30 days of age), with histologic and immunologic assessment 6 and 13 days after the second inoculation and bronchoprovocation testing 5-8 weeks later. Following the single RAIV inoculation, IgM and IgG1 measurements increased at 6, 11, and 15 DPI, with IgG1 being greater at 11 and 15 DPI. Nasal lesions were evident as early as 1 DPI and primarily involved the anterior dorsal medial meatus and adjacent dorsal atrio- and nasoturbinates. Alterations included epithelial cell exfoliation and necrosis, mild erosions, suppurative and nonsuppurative inflammation, intraepithelial neutrophil accumulations, and intraluminal exudate. By 3 DPI, olfactory epithelial damage was multifocal or locally diffuse, with degeneration of sensory cells and variable inflammation. By 13 DPI, lesions were essentially repaired. Minimal changes were apparent in the LRT despite evidence of viral replication in the lungs 24 hours after inoculation (> 3 log10 plaque-forming units/lung). Pups reinoculated with RAIV at 30 days of age did not develop significant histologic lesions, nor did they exhibit increased airway responsiveness when assessed as young adults. In spite of their immature immune status at the time of initial infection, 13 days after the second RAIV inoculation, IgG1 increased substantially. Thus, neonatal RAIV infection resulted in acute nasal epithelial injury and inflammation, alterations that may allow subsequent evaluation of viral disease-air pollutant interactions.

Influenza virus host resistance models in mice and rats: utilization for immune function assessment and immunotoxicology

Each year influenza viruses are responsible for epidemic respiratory diseases with excess morbidity and mortality. The severity of influenza diseases ranges from mild upper respiratory tract infections to severe lower respiratory tract infections involving pneumonia, bronchiolitis and coincidental bacterial super-infections. The immune response to influenza viruses can be schematically divided into a cascade of non-specific and specific functions. These functions are involved at different well defined time points after infection. We describe in this manuscript three influenza models utilized in our laboratory: (i) a highly virulent influenza virus (influenza A/Hong Kong/8/68 (H3N2) virus) adapted to B6C3F1 mice, (ii) a mouse-adapted influenza A/Port Chalmers/1/73 (H3N2) virus, and (iii) a rat-adapted influenza virus (RAIV) model (influenza A/Port Chalmers/1/73 (H3N2)). This rat-adapted influenza model has been mainly utilized as a model to assess local immunotoxic effects of inhaled environmental pollutants such as phosgene. These host resistance models are also useful for assessing the effect of systemically-induced immunosuppression or immunomodulation by drugs or chemicals on the local pulmonary immune response to influenza virus. The comparison of these different models allowed two major conclusions: (a) viral replication and mortality are two different endpoints and are not necessarily linked (no mortality was observed with Port Chalmers virus in the mouse although the virus replicates to high titers in the lung with a kinetic pattern comparable to the one obtained with Hong Kong virus), (b) mortality, viral replication, and immune function assessment are different endpoints that can be used, depending on the question addressed.

Enhanced and prolonged pulmonary influenza virus infection following phosgene inhalation

Animal infectivity models have been important in the demonstration of enhanced susceptibility to viral and bacterial infection as a result of low-level toxicant exposure. This study demonstrated an enhanced and prolonged viral infection using an influenza virus infectivity model in the rat following exposure to the toxicant gas phosgene. Fischer-344 rats exposed to either air or a sublethal concentration of phosgene demonstrated peak pulmonary influenza virus titers 1 d after infection. Virus titers in rats exposed to air declined rapidly falling below detectable levels by 4 d after infection. However, a significantly enhanced and prolonged pulmonary influenza virus infection was observed on d 3 and 4 after infection in rats exposed to phosgene. Virus was cleared below detectable limits on d 5 after infection in animals exposed to phosgene. Thus, inhalation of sublethal concentrations of phosgene resulted in an increased severity of pulmonary influenza virus infection. This study provides a demonstration of the effective use of a rat viral infectivity model to detect the immunotoxicity of inhaled pollutants. This model will allow future studies to focus on the immunological mechanism(s) responsible for the enhanced and prolonged pulmonary influenza virus infection.