Multimorbidity and Functional Limitations Among Adults 65 or Older, NHANES 2005-2012.

INTRODUCTION: The development of functional limitations among adults aged 65 or older has profound effects on individual and population resources. Improved understanding of the relationship between functional limitations and co-occurring chronic diseases (multimorbidity) is an emerging area of interest. The objective of this study was to investigate the association between multimorbidity and functional limitations among community-dwelling adults 65 or older in the United States and explore factors that modify this association. METHODS: We conducted a cross-sectional analysis of adults aged 65 or older using data from the National Health and Nutrition Examination Survey (NHANES) from 2005 through 2012. We used negative binomial regression to estimate the association between multimorbidity (≥2 concurrent diseases) and functional limitations and to determine whether the association differed by sex or age. RESULTS: The prevalence of multimorbidity in this population was 67% (95% confidence interval [CI], 65%-68%). Each additional chronic condition was associated with an increase in the number of functional limitations, and the association was stronger among those aged 75 or older than among those aged 65 to 74. For those aged 65 to 74, each additional chronic condition was associated with 1.35 (95% CI, 1.27-1.43) times the number of functional limitations for men and 1.62 times (95% CI, 1.31-2.02) the number of functional limitations for women. For those 75 or older, the associations increased to 1.71 (95% CI, 1.35-2.16) for men and 2.06 (95% CI, 1.51-2.81) for women for each additional chronic condition. CONCLUSION: Multimorbidity was associated with increases in functional limitations, and the associations were stronger among women than among men and among adults aged 75 or older than among those aged 65 to 74. These findings underscore the importance of addressing age and sex differences when formulating prevention strategies.

Activation of the aryl hydrocarbon receptor during development enhances the pulmonary CD4+ T-cell response to viral infection.

Respiratory infections are a threat to health and economies worldwide, yet the basis for striking variation in the severity of infection is not completely understood. Environmental exposures during development are associated with increased severity and incidence of respiratory infection later in life. Many of these exposures include ligands of the aryl hydrocarbon receptor (AHR), a transcription factor expressed by immune and nonimmune cells. In adult animals, AHR activation alters CD4(+) T cells and changes immunopathology. Developmental AHR activation impacts CD4(+) T-cell responses in lymphoid tissues, but whether skewed responses are also present in the infected lung is unknown. To determine whether pulmonary CD4(+) T-cell responses are modified by developmental AHR activation, mice were exposed to the prototypical AHR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin during development and infected with influenza virus as adults. Lungs of exposed offspring had greater bronchopulmonary inflammation compared with controls, and activated, virus-specific CD4(+) T cells contributed to the infiltrating leukocytes. These effects were CD4(+) T cell subset specific, with increases in T helper type 1 and regulatory T cells, but no change in the frequency of T helper type 17 cells in the infected lung. This is in direct contrast to prior reports of suppressed conventional CD4(+) T-cell responses in the lymph node. Using adoptive transfers and manipulating the pathogen properties, we determined that developmental exposure influenced factors intrinsic and extrinsic to CD4(+) T cells and may involve developmentally induced changes in signals from infected lung epithelial cells. Thus developmental exposures lead to context-dependent changes in pulmonary CD4(+) T-cell subsets, which may contribute to differential responses to respiratory infection.

Alcohol consumption suppresses mammary tumor metastasis in a syngeneic tumor transplantation model.

Epidemiological studies indicate a positive correlation between alcohol consumption and the risk of developing breast cancer. However, little is known about whether alcohol consumption affects breast cancer metastasis. Considering that the primary cause of death in breast cancer patients is due to metastasis, further insight into whether alcohol consumption influences disease progression and survival is needed. We tested the effect of alcohol consumption on breast cancer metastasis using the 4T1.2 syngeneic mammary tumor model in Balb/c mice. The treatment groups included a High-consuming group (18 % w/v alcohol in drinking water), a Moderate-consuming group (5 % w/v), a Low-consuming group (1 % w/v), and a Water-drinking control group. 4T1.2 mammary tumor cells were injected orthotopically into the mammary fat pad. Metastases were enumerated in lungs and in distant mammary glands 4 weeks after injection. Consumption of High alcohol protected against metastasis, as High-consuming mice typically had 65-75 % fewer metastases compared to Water-drinking controls. A suggestive reduction in tumor spread was observed in the Moderate-drinking group, although the effects did not reach statistical significance. Consumption of the Low alcohol dose did not affect metastasis. CXCR4 expression in the primary tumors was significantly reduced by High alcohol consumption; however, expression of this chemokine receptor in the primary tumor did not correlate with metastatic potential. Additional studies were conducted to test for possible direct effects of 0.3 % w/v ethanol on tumor cell proliferation, migration, invasion, and colony formation of 4T1.2 cells in vitro. Our results indicate that, for this murine model, alcohol consumption does not exacerbate tumor metastasis, and that High alcohol consumption reduces tumor spread.

Aryl hydrocarbon receptor activation during pregnancy, and in adult nulliparous mice, delays the subsequent development of DMBA-induced mammary tumors.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), the prototypic ligand for the aryl hydrocarbon receptor (AhR), promotes tumor formation in some model systems. However, with regard to breast cancer, epidemiological and animal studies are inconclusive as to whether exposure increases tumor incidence or may instead be protective. We have previously reported that mice exposed to TCDD during pregnancy have impaired differentiation of mammary tissue, including decreased branching and poor development of lobuloalveolar structures. Because normal pregnancy-induced mammary differentiation may protect against subsequent neoplastic transformation, we hypothesized that TCDD-treated mice would be more susceptible to chemical carcinogenesis after parturition. To test this, mice were treated with TCDD or vehicle during pregnancy. Four weeks later, 7,12-dimethylbenz[a]anthracene (DMBA) was administered to induce mammary tumor formation. Contrary to our hypothesis, TCDD-exposed parous mice showed a 4-week delay in tumor formation relative to controls, and they had a lower tumor incidence throughout the 27-week time course. The same results were obtained in nulliparous mice given TCDD and DMBA on the same schedule. We next addressed whether the delayed tumor incidence was a reflection of decreased tumor initiation, by testing the formation of DMBA-DNA adducts and preneoplastic lesions, induction of cytochrome P450s, and cell proliferation. None of these markers of tumor initiation differed between vehicle- and TCDD-treated animals. The expression of CXCL12 and CXCR4 was also measured to address their possible role in tumorigenesis. Taken together, our results suggest that AhR activation by TCDD slows the promotion of preneoplastic lesions to overt mammary tumors.

Activation of the aryl hydrocarbon receptor is essential for mediating the anti-inflammatory effects of a novel low-molecular-weight compound.

VAF347 is a low-molecular-weight compound that inhibits allergic lung inflammation in vivo. This effect is likely the result of a block of dendritic cell (DC) function to generate proinflammatory T-helper (Th) cells because VAF347 inhibits interleukin (IL)-6, CD86, and human leukocyte antigen (HLA)-DR expression by human monocyte-derived DC, 3 relevant molecules for Th-cell generation. Here we demonstrate that VAF347 interacts with the aryl hydrocarbon receptor (AhR) protein, resulting in activation of the AhR signaling pathway. Functional AhR is responsible for the biologic activity of VAF347 because (1) other AhR agonists display an identical activity profile in vitro, (2) gene silencing of wild-type AhR expression or forced overexpression of a trans-dominant negative AhR ablates VAF347 activity to inhibit cytokine induced IL-6 expression in a human monocytic cell line, and (3) AhR-deficient mice are resistant to the compound's ability to block allergic lung inflammation in vivo. These data identify the AhR protein as key molecular target of VAF347 and its essential role for mediating the anti-inflammatory effects of the compound in vitro and in vivo.

A dose-response study of the effects of prenatal and lactational exposure to TCDD on the immune response to influenza a virus.

The goal of the current study was to evaluate the immune response to a common respiratory pathogen, influenza A virus, in mice exposed to increasing doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) during development. Additionally, the treatment paradigm was designed to provide exposure throughout fetal and neonatal development, beginning on d 1 of gestation. To accomplish this, impregnated C57Bl/6 mice were treated with 0.25 microg/kg TCDD on d 0 and 7 of pregnancy, followed by 2 additional doses of 0.25, 1, or 5 microg/kg given on d 14 and postpartum d 2. The adult offspring were infected with influenza virus, and components of the adaptive and innate immune responses were evaluated. Our results show that developmental exposure to TCDD dose-responsively suppressed both the cell-mediated and antibody responses to influenza virus in female but not males. In contrast, TCDD exposure enhanced the innate immune responses in offspring of both sexes; specifically, neutrophilia and interferon (IFN) gamma levels in the lung were increased. These alterations in functional immunity did not result from overt toxicity to the immune organs, as developmental TCDD exposure did not alter the cellular composition of the thymus, spleen, or bone marrow. These findings extend our knowledge of the dose-responsive nature of immunological defects induced by developmental exposure to TCDD and offer insight regarding the dose required to alter the immune response to viral infection. Moreover, we demonstrate a clear dose at which no observable effects on immune function later in life were detected.

Activation of the aryl hydrocarbon receptor diminishes the memory response to homotypic influenza virus infection but does not impair host resistance.

Although suppression of a primary immune response by aryl hydrocarbon receptor (AhR) ligands is well known, few studies have explicitly examined the effects of AhR agonists on immunological memory. Therefore, the goal of this study was to characterize the anamnestic response to influenza virus in mice exposed to the most potent AhR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Mice were given a single dose of TCDD, which caused suppression of the primary response, and kinetics of the recall antibody and CD8(+) T cell responses to homotypic infection were monitored. Two to three months after primary infection, virus-specific IgG levels were suppressed in mice treated with TCDD, and remained suppressed after reinfection. In contrast, IgA levels were enhanced in the TCDD-treated group. The recall response of virus-specific CD8(+) T cells was also suppressed, as the number of virus-specific memory CD8(+) T cells was diminished, and the kinetics of the recall response was delayed. No morbidity or mortality was observed in vehicle- or TCDD-treated mice, and mice in both groups cleared the virus within three days after reinfection. Thus, with regard to understanding how activation of the AhR during a primary immune response affects the generation of immunological memory, our data present a mixed story. On one hand, TCDD treatment reduced the primary response, resulting in lower levels of virus-specific IgG and diminution of the memory CD8 pool. However, the secondary response to homotypic infection was nevertheless host-protective. These findings have implications for determining the mechanisms by which AhR ligands adversely affect lymphocyte function and understanding the mechanisms that control the acquisition of immunological memory.

Influence of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the antigen-presenting activity of dendritic cells.

We have previously shown that exposure of mice to 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) induces activation-like changes in splenic dendritic cells (DC) in the absence of antigen challenge. Since activation of DC reduces their ability to phagocytize antigen, we examined the effects of TCDD on the ability of DC to process and present antigen to antigen-specific T cells and to internalize latex beads. Additionally, the expression of costimulatory and adhesion molecules was examined on DC from TCDD-treated mice injected with allogeneic tumor cells. The ability of DC from C57Bl/6 mice to induce proliferation of keyhole limpet hemocyanin (KLH)-specific 10.5.17 T cells and production of IL-4 was not significantly altered by TCDD exposure, either when KLH was added in vitro or when the mice were injected with KLH prior to DC isolation. In contrast, ovalbumin (OVA) presentation by DC from TCDD-treated Balb/c mice induced enhanced proliferation of OVA-specific D011.10 T cells, although the production of IL-2 and IFN-gamma was not affected. Enhanced in vivo proliferation of adoptively transferred, CFSE-labeled DO11.10 T cells was also observed in TCDD-treated Balb/c mice that were challenged with OVA. TCDD treatment modulated the expression of major histocompatibility complex (MHC) class II, CD24, ICAM-1, CD40, and LFA-1 on splenic DC from C57Bl/6 mice injected with allogeneic tumor cells; however, the effects of TCDD were identical to changes seen previously in nonimmune mice, suggesting that these effects were not antigen-dependent. Finally, TCDD treatment did not affect the ability of splenic DC to internalize latex beads administered in vivo. Taken together, these results suggest that the activation-like changes induced in DC by TCDD do not suppress the ability of DC to process and present antigen, but may enhance their ability to provide activation signals to T cells. This, in turn, may alter the survival of the T cells, the DC, or both, and might lead to dysregulation of the immune response.

A novel effect of dioxin: exposure during pregnancy severely impairs mammary gland differentiation.

Many ligands for the aryl hydrocarbon receptor (AhR) are considered endocrine disruptors and carcinogens, and assessment of adverse health effects in humans exposed to such chemicals has often focused on malignancies, including breast cancer. Mammary tissue contains the AhR, and inappropriate activation of the AhR during fetal development causes defects in mammary development that persist into adulthood. However, it is not known whether the extensive differentiation of mammary tissue that occurs during pregnancy is also sensitive to disruption by AhR activation. To examine this, we exposed pregnant C57Bl/6 mice to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on days 0, 7, and 14 of pregnancy. Examination of mammary glands on days 9, 12, and 17 of pregnancy and on the day of parturition showed severe defects in development, including stunted growth, decreased branching, and poor formation of lobular alveolar structures. This impaired differentiation was biologically significant, as expression of whey acidic protein in the gland was suppressed, and all pups born to TCDD-treated dams died within 24 h of birth. Analysis of circulating progesterone, prolactin, and estradiol suggest that hormone production was slightly impaired by inappropriate activation of the AhR. However, hormone levels were affected only very late in pregnancy. Given that the observed defects in gland development preceded these hormonal effects, altered hormone levels are an unlikely mechanistic explanation for impaired mammary development. This novel finding that AhR activation during pregnancy disrupts mammary gland differentiation raises questions about the susceptibility of mammary tissue to direct injury by endocrine disrupting agents and the potential for AhR-mediated signaling to adversely affect lactation and breast tissue development in human populations.

Examining the relationship between impaired host resistance and altered immune function in mice treated with TCDD.

Exposure to TCDD suppresses the immune response to numerous antigens, including bacterial and viral pathogens. Although we administer a non-lethal infection with influenza A virus, we often observe significant mortality in TCDD-treated animals. With the goal of identifying which TCDD-induced defects impair host resistance, we conducted a dose response study to examine whether alteration of particular immunological endpoints could be correlated with mortality. C57Bl/6 mice were treated with vehicle control, or 1, 2.5, 5, 7.5 or 10 microg/kg TCDD 1 day prior to intranasal (i.n.) infection with influenza virus. Survival was monitored for 9 days, when remaining mice were sacrificed and multiple endpoints evaluated. Lymphocyte migration to the lung and the production of virus-specific IgG2a, IgG1, and IgG2b antibodies were significantly diminished, even at the lower doses. IgA was enhanced in all groups treated with TCDD. In contrast, T cell expansion in the lymph node, and the production of IFNgamma and IL-12 were relatively resistant to suppression. Treatment with TCDD also enhanced pulmonary neutrophilia in infected mice. These results suggest that decreased antibody production and hyperinflammation may contribute to the death of TCDD-treated mice, and underscore the importance of evaluating numerous endpoints before concluding that a chemical is or is not immunotoxic.

New insights into the aryl hydrocarbon receptor as a modulator of host responses to infection.

The host response to infection is known to be influenced by many factors, including genetics, nutritional status, age, as well as drug and chemical exposures. Recent advances reveal that the aryl hydrocarbon receptor (AhR) modulates aspects of the innate and adaptive immune response to viral, bacterial, and parasitic organisms. Although many of these observations were made using the high affinity but poorly metabolized AhR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), not all of the effects are detrimental to the host. Sometimes AhR activation, even with TCDD, was beneficial and improved host resistance and survival. A similar dichotomy is observed in infected AhR-deficient mice, wherein absence of functional AhR sometimes, but not always, alters host resistance. When examined in their totality, current data indicate that AhR controls multiple regulatory pathways that converge with infection-associated signals and depending on the context (e.g., type of pathogen, site of infection), lead to distinct outcomes. This creates numerous exciting opportunities to harness the immunomodulatory action of AhR to transform host responses to infection. Moreover, since many of the mechanisms cued in response to infectious agents are pivotal in the context of other diseases, there is much to be learned about AhR's cellular targets and molecular mechanisms of action.

Mechanistic exploration of AhR-mediated host protection against Streptococcus pneumoniae infection.

Streptococcus pneumoniae is a primary cause of invasive bacterial infection and pneumonia and is one of the leading causes of death worldwide. In prior studies we showed that pre-treating mice with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent agonist of the aryl hydrocarbon receptor (AhR), protects against S. pneumoniae-induced mortality and reduces pulmonary bacterial burden. The current studies were conducted to help elucidate the mechanism for this protective effect, and to characterize the response in the lung during the first 10h following infection. C57Bl/6 mice were treated with TCDD one day prior to intranasal infection with serotype 3 S. pneumoniae. Monitoring of bacteria in the lung airways revealed that bacterial growth was inhibited in the TCDD-treated animals within 10h of infection. To address the mechanism of this rapid protective response, macrophages, neutrophils, and invariant Natural Killer T (iNKT) cells were quantified, and levels of natural antibodies produced by B-1 B cells were evaluated. Functional assays addressed whether AhR activation reduced the capacity of lung epithelial cells to bind bacteria, and whether TCDD treatment enhanced production of antimicrobial agents in the lung or blood. None of the hypothesized mechanisms was able to explain the protective effect. Finally, the exposure paradigm was manipulated to test whether administration of TCDD after instillation of the bacteria was also protective. Results showed that TCDD must be administered in advance of exposure to bacteria, suggesting that the lung environment is rendered inhospitable to the pathogens.

Activation of the aryl hydrocarbon receptor by TCDD inhibits mammary tumor metastasis in a syngeneic mouse model of breast cancer.

Treatment with aryl hydrocarbon receptor (AhR) agonists can slow or reverse the growth of primary mammary tumors in rodents, which has fostered interest in developing selective AhR modulators for treatment of breast cancer. However, the major goal of breast cancer therapy is to inhibit metastasis, the primary cause of mortality in women with this disease. Studies conducted using breast cancer cell lines have demonstrated that AhR agonists suppress proliferation, invasiveness, and colony formation in vitro; however, further exploration using in vivo models of metastasis is warranted. To test the effect of AhR activation on metastasis, 4T1.2 mammary tumor cells were injected into the mammary gland fat pad of syngeneic Balb/c mice treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Primary tumor growth was monitored for 4 weeks, at which time metastasis was determined. TCDD treatment suppressed metastasis by approximately 50%, as measured both in the lung and in mammary glands at sites distant from the primary tumor. Primary tumor growth was not suppressed by TCDD exposure nor was proliferation of 4T1.2 cells affected by TCDD treatment in vitro. Taken together, these results suggest that the protective effect of AhR activation was selective for the metastatic process and not simply the result of a direct decrease in tumor cell proliferation or survival at the primary site. These observations in immunologically intact animals warrant further investigation into the mechanism of the protective effects of AhR activation and support the promise for use of AhR modulators to treat breast cancer.

Targeting migration inducting gene-7 inhibits carcinoma cell invasion, early primary tumor growth, and stimulates monocyte oncolytic activity.

Expression of Migration inducting gene-7 (Mig-7) is limited to tumor cells and to date not found in normal tissues. Multiple tumor microenvironment factors, such as epidermal and hepatocyte growth factors, in concert with alphavbeta5 integrin ligation, induce Mig-7 mRNA expression. Gain or loss of Mig-7 protein studies shows that Mig-7 promotes invasion of colon and endometrial carcinoma cells. These data led us to hypothesize that targeting Mig-7 through various methods could decrease invasion, enhance monocyte cell killing of tumor cells, and inhibit disease progression. To begin testing this hypothesis, an in vitro chemoinvasion assay of endometrial carcinoma cells treated with Mig-7-specific or control antibodies was used. Mig-7 antibody significantly reduced invasion by >60% compared with controls. In another approach to test this hypothesis, an in vitro analysis of peptide-stimulated human peripheral blood monocyte cells and their killing of MCF-7 breast carcinoma cells was used. Mig-7 peptide treatment increased monocyte cell tumor necrosis factor expression and killing of MCF-7 cells 30-fold over no peptide stimulation and 3-fold over MUC-1 or control peptide treatments. Furthermore, stably expressing Mig-7-specific short hairpin RNA resulted in significantly reduced Mig-7 protein levels and early primary tumor growth in a xenograft nude mouse model. Reduced phosphorylation of ERK1/2, Akt, and S6 kinase as well as decreased membrane-type 1 matrix metalloproteinase activity were mechanisms through which Mig-7 protein caused these effects. Based on these collective data, Mig-7 expression could be a potential candidate for future targeted cancer therapies.

Protection against lethal challenge with Streptococcus pneumoniae is conferred by aryl hydrocarbon receptor activation but is not associated with an enhanced inflammatory response.

Streptococcus pneumoniae is a common respiratory pathogen and a major cause of morbidity and mortality in humans, particularly in the elderly and young children. The pulmonary immune response to S. pneumoniae is initiated very rapidly, and, ideally, innate immune responses are able to contain bacterial colonization. In the studies presented here, we sought to determine whether activation of the aryl hydrocarbon receptor (AhR) would protect mice from an otherwise lethal infection with S. pneumoniae. The rationale for this hypothesis is that, although most AhR agonists are potent immunosuppressants, AhR activation enhances the inflammatory response to pathogenic and nonpathogenic stimuli. Specifically, neutrophil numbers and levels of inflammatory cytokines are often increased in mice treated with the potent AhR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). To test the hypothesis, vehicle control- or TCDD-treated mice were intranasally infected with S. pneumoniae. Mortality, pulmonary bacterial burden, cytokine/chemokine levels, and influx of immune cells to the lung were analyzed at various times postinfection. As predicted, survival was substantially improved in the mice treated with TCDD, and the pulmonary bacterial burden was decreased. Surprisingly, however, there was no evidence suggesting that protection resulted from an enhanced inflammatory response. In fact, neutrophil numbers and inflammatory chemokines and cytokines were all decreased in the TCDD-treated mice relative to vehicle control-treated mice. This suggests that the protective effect of AhR activation is not the result of altered immune function but instead may reflect a direct effect on the response of lung cells to infection.

Developmental exposure to the potent aryl hydrocarbon receptor agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin Impairs the cell-mediated immune response to infection with influenza a virus, but enhances elements of innate immunity.

Based on demonstrated effects on functional immunity in rodent models and supportive evidence from epidemiological studies, it is apparent that developmental exposure to ligands for the aryl hydrocarbon receptor (AhR) has the potential to impair immunity in human populations. Furthermore, due to the high levels of these compounds detected in human breast milk, and the fact that they cross the placenta, it is clear that humans are exposed to AhR ligands during fetal and neonatal development. The current studies were conducted to further characterize the relationship between developmental exposure to TCDD, the most potent AhR agonist, and defects in immune function later in life. Impregnated C57Bl/6 mice were treated with 4 doses of 1 mircog/kg TCDD, given on days 0, 7, and 14 of pregnancy, and 2 days after parturition. Functional immunity was assessed by challenging the adult offspring with influenza virus. Both male and female offspring of the TCDD-treated dams demonstrated impairment of the adaptive immune response, as evidenced by suppressed numbers of T cells and IFNgamma-producing cells in the draining lymph nodes and reduced T cell recruitment to the lung. In contrast, the inflammatory response, including infection-associated pulmonary neutrophilia and IFNgamma levels, was significantly elevated in the developmentally-exposed mice. These functional defects in immunity were not correlated with defects in hematopoeisis, as immune cells in the bone marrow, spleen, and thymus were phenotypically normal in uninfected mice. These results support the idea that immune alterations that arise during development cause persistent and significant changes in immune function.

Fewer CTL, not enhanced NK cells, are sufficient for viral clearance from the lungs of immunocompromised mice.

Activation of the aryl hydrocarbon receptor (AhR) causes numerous defects in anti-viral immunity, including suppressed CTL generation and impaired host resistance. However, despite a reduced CTL response, mice that survive infection clear the virus. Therefore, we examined the contribution of NK cells and pro-inflammatory cytokines to viral clearance in influenza virus-infected mice exposed to TCDD, the most potent AhR agonist. Infection caused transient increases in pulmonary TNFalpha, IL-1, and IFNalpha/beta levels, but neither the kinetics nor magnitude of this response was affected by AhR activation. No IL-18 was detected at any time point examined. Exposure to TCDD enhanced NK cell numbers in the lung but did not affect their IFNgamma production. Furthermore, depletion of NK cells did not alter anti-viral cytolytic activity. In contrast, removal of CD8+ T cells ablated virus-specific cytolytic activity. These results demonstrate that the pulmonary CTL response to influenza virus is robust and few CTL are necessary for viral clearance.