Sendai virus pneumonia: evidence for the early recruitment of gamma delta T cells during the disease course

Sendai virus C protein affects macrophage function, which plays a critical role in modulating disease severity during Sendai virus infection in mice

Sendai virus (SeV) accessory protein C limits the generation of double-stranded RNAs, defective interfering RNAs, or both, during viral transcription and replication, thereby limiting interferon-β production. Our recent in vitro analyses on murine macrophage cell lines demonstrated that this protein also contributes to restricting macrophage function, including the production of nitric oxide (NO) and inflammatory cytokines in addition to interferon-β, in infected macrophages. This study showed that depletion of airway macrophages by clodronate-loaded liposomes led to the development of severe viral pneumonia in recombinant C gene-knockout SeV (SeV∆C)-infected mice, but did not modulate disease severity in wild-type SeV-infected mice. Furthermore, the severe disease observed in macrophage-depleted, SeV∆C-infected mice was associated with exacerbated virus replication in the lungs, leading to severe airway inflammation and pulmonary edema, indicating lung injury. These results suggested that the antimacrophage activity of SeV C protein might play a critical role in modulating lung injury and associated diseases caused by SeV.

Making a case for using γδ T cells against SARS-CoV-2

Intensive worldwide efforts are underway to determine both the pathogenesis of SARS-CoV-2 infection and the immune responses in COVID-19 patients in order to develop effective therapeutics and vaccines. One type of cell that may contribute to these immune responses is the γδ T lymphocyte, which plays a key role in immunosurveillance of the mucosal and epithelial barriers by rapidly responding to pathogens. Although found in low numbers in blood, γδ T cells consist the majority of tissue-resident T cells and participate in the front line of the host immune defense. Previous studies have demonstrated the critical protective role of γδ T cells in immune responses to other respiratory viruses, including SARS-CoV-1. However, no studies have profoundly investigated these cells in COVID-19 patients to date. γδ T cells can be safely expanded in vivo using existing inexpensive FDA-approved drugs such as bisphosphonate, in order to test its protective immune response to SARS-CoV-2. To support this line of research, we review insights gained from previous coronavirus research, along with recent findings, discussing the potential role of γδ T cells in controlling SARS-CoV-2. We conclude by proposing several strategies to enhance γδ T cell's antiviral function, which may be used in developing therapies for COVID-19.

γδT cells suppress inflammation and disease during rhinovirus-induced asthma exacerbations

Most asthma exacerbations are triggered by virus infections, the majority being caused by human rhinoviruses (RV). In mouse models, γδT cells have been previously demonstrated to influence allergen-driven airways hyper-reactivity (AHR) and can have antiviral activity, implicating them as prime candidates in the pathogenesis of asthma exacerbations. To explore this, we have used human and mouse models of experimental RV-induced asthma exacerbations to examine γδT-cell responses and determine their role in the immune response and associated airways disease. In humans, airway γδT-cell numbers were increased in asthmatic vs. healthy control subjects during experimental infection. Airway and blood γδT-cell numbers were associated with increased airways obstruction and AHR. Airway γδT-cell number was also positively correlated with bronchoalveolar lavage (BAL) virus load and BAL eosinophils and lymphocytes during RV infection. Consistent with our observations of RV-induced asthma exacerbations in humans, infection of mice with allergic airways inflammation increased lung γδT-cell number and activation. Inhibiting γδT-cell responses using anti-γδTCR (anti-γδT-cell receptor) antibody treatment in the mouse asthma exacerbation model increased AHR and airway T helper type 2 cell recruitment and eosinophilia, providing evidence that γδT cells are negative regulators of airways inflammation and disease in RV-induced asthma exacerbations.

Human PIV-2 recombinant Sendai virus (rSeV) elicits durable immunity and combines with two additional rSeVs to protect against hPIV-1, hPIV-2, hPIV-3, and RSV

The human parainfluenza viruses (hPIVs) and respiratory syncytial viruses (RSVs) are the leading causes of hospitalizations due to respiratory viral disease in infants and young children, but no vaccines are yet available. Here we describe the use of recombinant Sendai viruses (rSeVs) as candidate vaccine vectors for these respiratory viruses in a cotton rat model. Two new Sendai virus (SeV)-based hPIV-2 vaccine constructs were generated by inserting the fusion (F) gene or the hemagglutinin-neuraminidase (HN) gene from hPIV-2 into the rSeV genome. The inoculation of either vaccine into cotton rats elicited neutralizing antibodies toward both homologous and heterologous hPIV-2 virus isolates. The vaccines elicited robust and durable antibodies toward hPIV-2, and cotton rats immunized with individual or mixed vaccines were fully protected against hPIV-2 infections of the lower respiratory tract. The immune responses toward a single inoculation with rSeV vaccines were long-lasting and cotton rats were protected against viral challenge for as long as 11 months after vaccination. One inoculation with a mixture of the hPIV-2-HN-expressing construct and two additional rSeVs (expressing the F protein of RSV and the HN protein of hPIV-3) resulted in protection against challenge viruses hPIV-1, hPIV-2, hPIV-3, and RSV. Results identify SeV vectors as promising vaccine candidates for four different paramyxoviruses, each responsible for serious respiratory infections in children.

Antiviral reactivities of gammadelta T cells

The complex antiviral immune mechanisms involve both adaptive and innate reactions mediated by γδ T lymphocytes, whose unique immunosurveillance contributions are analyzed here in different clinical and experimental settings. It is beyond any doubt that the fast, potent, cytotoxic as well as non-cytolytic antiviral activities of γδ T cells are critical in protecting the host against diverse viral pathogens.

Acute effects of parainfluenza virus on epithelial electrolyte transport

Parainfluenza viruses are important causes of respiratory disease in both children and adults. In particular, they are the major cause of the serious childhood illness croup (laryngotracheobronchitis). The infections produced by parainfluenza viruses are associated with the accumulation of ions and fluid in the respiratory tract. It is not known, however, whether this accumulation is because of a direct effect of the viruses on ion and fluid transport by the respiratory epithelium. Here we show that a model parainfluenza virus (the Sendai virus), in concentrations observed during respiratory infections, activates Cl- secretion and inhibits Na+ absorption across the tracheal epithelium. It does so by binding to a neuraminidase-insensitive glycolipid, possibly asialo-GM1, triggering the release of ATP, which then acts in an autocrine fashion on apical P2Y receptors to produce the observed changes in ion transport. These findings indicate that fluid accumulation in the respiratory tract associated with parainfluenza virus infection is attributable, at least in part, to direct effects of the virus on ion transport by the respiratory epithelium.

Infiltration of T-lymphocytes in the brain after anterior chamber inoculation of a neurovirulent and neuroinvasive strain of HSV-1

Following anterior chamber (AC) inoculation of BALB/c mice with the KOS strain of herpes simplex virus type 1 (HSV-1), or with H129, a neuroinvasive and neurovirulent strain of HSV-1, both strains of virus spread from the injected eye through the brain to cause retinitis. However, KOS-infected mice develop retinitis in the uninoculated eye only, whereas H129-infected mice develop bilateral retinitis. Previous studies have shown that infiltrating T-cells in the suprachiasmatic nuclei (SCN) of the hypothalamus of KOS-infected mice concomitant with or before virus protect KOS-infected mice from ipsilateral retinitis. To determine the timing of T cell infiltration and cytokine production in the brain of H129-infected mice, adjacent, frozen sections of the brain were immunostained for virus, T-cells, IL-2, TNF-alpha or IFN-gamma. T-cells infiltrated the brains of H129-infected mice and cytokines were produced in infected tissues. However, virus spread to the optic nerve and retina of both the inoculated and uninoculated eye before T-cells and cytokines were detected in the SCN of H129-infected mice. These results suggest that infiltrating T-cells in the SCN of H129-infected mice may arrive too late to prevent the spread of virus into the optic nerves and retinas and thus prevent development of bilateral retinitis in infected mice.

Immunohistological study of infiltrated cells and cytokines in murine herpetic keratitis

PURPOSE

To identify localization and kinetics of infiltrated cells and cytokines in murine herpetic keratitis.

METHODS

HSV-1 was inoculated onto the scarified BALB/c corneas. At given times post infection (PI), eyes were removed and studied immunohistochemically using monoclonal antibodies against several infiltrated cells and cytokines.

RESULTS

Neutrophils and NK cells infiltrated as early as 1 day PI reaching a maximum number at 2 day PI in initial stage. gamma delta TCR positive cells were observed in the corneal stroma from 1 day PI to 8 day PI. IL-2 and IFN-gamma were positive in the cell-infiltrated areas of the epithelial and stromal lesions, whereas IL-4 was negative throughout the experiment.

CONCLUSION

Our results indicated that cytokine profile upon herpes infection on the cornea is Th1 dominant. Together with neutrophils in the early phase of infection, gamma delta positive T cells may play an additional role in protecting the cornea against incoming pathogens.

gammadelta(+) T-Lp6phocyte cytotoxicity against envelope-expressing target cells is unique to the alymphocytic state of bovine leukemia virus infection in the natural host

Bovine leukemia virus (BLV) is a complex B-lymphotrophic retrovirus of cattle and the causative agent of enzootic bovine leukosis. Serum antibody in infected animals does not correlate with protection from disease, yet only some animals develop severe disease. While a cytotoxic T-lymphocyte response may be responsible for directing BLV pathogenesis, this possibility has been left largely unexplored, in part since the lack of readily established cytotoxic target cells in cattle has hampered such studies. Using long-term naturally infected alymphocytic (AL) cattle, we have established the existence of cytotoxic T-lymphocyte response against BLV envelope proteins (Env; gp51/gp30). In vitro-expanded peripheral blood mononuclear (PBM) cell effector populations consisted mainly of gammadelta(+) (>40%), CD4(+) (>35%), and CD8(+) (>10%) T lymphocytes. Specific lysis of autologous fibroblasts infected with recombinant vaccinia virus (rVV) delivering the BLV env gene ranged from 30 to 65%. Depletion studies indicated that gammadelta(+) and not CD8(+) T cells were responsible for the cytotoxicity against autologous rVVenv-expressing fibroblasts. Additionally, cultured effector cells lysed rVVenv-expressing autologous fibroblasts and rVVenv-expressing xenogeneic targets similarly, suggesting a lack of genetic restricted killing. Restimulation of effector populations increased the proportion of gammadelta(+) T cells and concomitantly Env-specific cytolysis. Interestingly, culture of cells from BLV-negative or persistently lymphocytic cattle failed to elicit such cytotoxic responses or increase in gammadelta(+) T-cell numbers. These results imply that cytotoxic gammadelta(+) T lymphocytes from only AL cattle recognize BLV Env without a requirement for classical major histocompatibility complex interactions. It is known that gammadelta(+) T lymphocytes are diverse and numerous in cattle, and here we show that they may serve a surveillance role during natural BLV infection.

Adoptive transfer of infectious bronchitis virus primed alphabeta T cells bearing CD8 antigen protects chicks from acute infection

Infectious bronchitis virus (IBV) infection and associated illness may be dramatically modified by passive transfer of immune T lymphocytes. Lymphocytes collected 10 days postinfection were transferred to naive chicks before challenge with virus. As determined by respiratory illness and viral load, transfer of syngeneic immune T lymphocytes protected chicks from challenge infection, whereas no protection was observed in the chicks receiving the MHC compatible lymphocytes from uninfected chicks. Protection following administration of T lymphocytes could be observed in chicks with three distinct MHC haplotypes: B(8)/B(8), B(12)/B(12), and B(19)/B(19). Nearly complete elimination of viral infection and illness was observed in chicks receiving cells enriched in alphabeta lymphocytes. In contrast, removal of gammadelta T lymphocytes had only a small effect on their potential to protect chicks. The adoptive transfer of enriched CD8(+) or CD4(+) T lymphocytes indicated that protection was also a function primarily of CD8-bearing cells. These results indicated that alphabeta T lymphocytes bearing CD8(+) antigens are critical in protecting chicks from IBV infection.

Interleukin-15 production at the early stage after oral infection with Listeria monocytogenes in mice

We previously reported that exogenous interleukin-15 (IL-15) induces proliferation and activation of intestinal intraepithelial lymphocytes (i-IEL) in naive mice. To investigate the ability of endogenous IL-15 to stimulate i-IEL in vivo, we monitored i-IEL and intestinal epithelial cells (i-EC) in mice after an oral infection with Listeria monocytogenes. Although the populations of alphabeta and gammadelta i-IEL were not significantly changed after the oral infection, the expression level of interferon-gamma (IFN-gamma) was increased both at transcriptional and protein levels, and a conversely marked decrease in interleukin-4 (IL-4) was detected in the i-IEL on day 1 after infection as compared with before infection. The T helper 1 (Th1)-biased response of i-IEL coincided with a peak response of IL-15 production in the i-EC after oral infection. These results suggested that IL-15 produced from i-EC may be at least partly involved in the stimulation of i-IEL to produce IFN-gamma after oral infection with L. monocytogenes.

TCRgammadelta cells and viruses

T-cell receptor gammadelta cells (TCRgammadelta) are often found in increased numbers during the course of several viral infections in humans. Although these findings suggest an important role for this unique subset, their precise function has not been ascertained. Recent studies in murine models of both RNA and DNA virus infections have begun to shed new light on the potential function for TCRgammadelta cells in antiviral immunity. It is clear that TCRgammadelta cells participate in the immune response to human immunodeficiency virus (HIV), influenza, Sendai, coxsackie, vaccinia, vesicular stomatitis virus (VSV), and herpes simplex virus-1 (HSV-1) viral infections since they become activated and home to the sites of viral replication. In this review we will summarize current efforts to dissect the role of TCRgammadelta cells in these disease settings, emphasizing the effector functions utilized, the TCR repertoire, and the antigens recognized. Particular focus will be placed on HSV-1 infections where we have begun to address these issues and have shown that TCRgammadelta cells are sufficient for protection from lethal infection and are able to recognize the herpes virus antigen glycoprotein I.

Phenotypic analysis of local cellular responses in calves infected with bovine respiratory syncytial virus

Changes in lymphocyte subsets in the trachea, pulmonary tissue, bronchoalveolar lavage (BAL), peripheral blood and bronchial lymph node (BLN) of gnotobiotic calves infected with bovine respiratory syncytial virus (BRSV) were analysed by flow cytometry. Following BRSV infection, virus titres in the nasopharynx reached a peak between days 5 and 7 and infection was resolving from day 10. Although calves did not develop signs of clinical respiratory disease, there was evidence of gross pneumonia and histological changes typical of BRSV bronchiolitis, which were most extensive from day 710 of infection. Following BRSV infection there was a recruitment of CD8+ T cells into the trachea and lung, which peaked on day 10 after infection. Thus, there were approximately equal numbers of CD8+ and CD4+ T cells in the lung and trachea of uninfected calves, whereas by day 10 of infection, CD8+ cells outnumbered CD4+ cells by 3:1 in the lungs and 6:1 in the trachea of the infected calves. Although the increase in CD4+ T cells into the lungs was less marked than that of CD8+ T cells, changes in expression of CD45R, CD45RO, L-selectin and interleukin-2 receptors all suggested that CD4+ T cells were activated during BRSV infection. Changes in gamma delta T cells were not observed in BRSV-infected calves. There was a marked increase in B cells in the BLN after infection and BLN CD4+ T cells changed from the majority expressing L-selectin and CD45R in uninfected calves to a predominance of L-selectin- CD45R- CD45RO+ phenotype, 10 days after infection. In conclusion, CD8+ T cells constitute the major lymphocyte subpopulation in the respiratory tract of calves recovering from BRSV infection.

Natural pathogens of laboratory mice, rats, and rabbits and their effects on research

Laboratory mice, rats, and rabbits may harbor a variety of viral, bacterial, parasitic, and fungal agents. Frequently, these organisms cause no overt signs of disease. However, many of the natural pathogens of these laboratory animals may alter host physiology, rendering the host unsuitable for many experimental uses. While the number and prevalence of these pathogens have declined considerably, many still turn up in laboratory animals and represent unwanted variables in research. Investigators using mice, rats, and rabbits in biomedical experimentation should be aware of the profound effects that many of these agents can have on research.

Gammadelta T cells in host defense and epithelial cell biology

Recent studies have demonstrated increased numbers of gammadelta T cells in a variety of human infectious as well as noninfectious diseases. In some cases gammadelta T cells could be shown to destroy infected or transformed cells. Advances in the identification of ligands recognized by gammadelta T cells and the development of animal model systems to study these cells in vivo should overcome some of the major obstacles currently preventing a better understanding of gammadelta T cell function in immune responses. As we gain this knowledge it may become possible to design therapeutic strategies exploiting unique properties of gammadelta T cells to promote more effective immunity.

T cell receptor-gamma/delta cells protect mice from herpes simplex virus type 1-induced lethal encephalitis

Increased numbers of T cell receptor (TCR)-gamma/delta cells have been observed in animal models of influenza and sendai virus infections, as well as in patients infected with human immunodeficiency virus and herpes simplex virus type 1 (HSV-1). However, a direct role for TCR-gamma/delta cells in protective immunity for pathogenic viral infection has not been demonstrated. To define the role of TCR-gamma/delta cells in anti-HSV-1 immunity, TCR-alpha-/- mice treated with anti- TCR-gamma/delta monoclonal antibodies or TCR-gamma/delta x TCR-alpha/beta double-deficient mice were infected with HSV-1 by footpad or ocular routes of infection. In both models of HSV-1 infection, TCR-gamma/delta cells limited severe HSV-1-induced epithelial lesions and greatly reduced mortality by preventing the development of lethal viral encephalitis. The observed protection resulted from TCR-gamma/delta cell-mediated arrest of both viral replication and neurovirulence. The demonstration that TCR-gamma/delta cells play an important protective role in murine HSV-1 infections supports their potential contribution to the immune responses in human HSV-1 infection. Thus, this study demonstrates that TCR-gamma/delta cells may play an important regulatory role in human HSV-1 infections.

Inflammatory infiltration of the upper airway epithelium during Sendai virus infection: involvement of epithelial dendritic cells

We undertook the present study to determine the nature of the cellular inflammatory response within the epithelial lining of the rat trachea during a Sendai virus infection. In particular, we aimed to investigate changes in the resident population of epithelial dendritic cells. Rats were infected with Sendai virus, and tracheal tissue was examined immunohistochemically at various times with a panel of cell-specific monoclonal antibodies. We found that Sendai virus infection was restricted to only the lumenal layer of epithelial cells and that virus nucleoprotein was present from days 2 to 5 postinfection. Starting around day 2 or 3, there was a large cellular influx consisting of macrophages, neutrophils, NK cells, and T cells; this coincided with expression of high levels of ICAM-1 on the basal (uninfected) layers of the epithelium. The T cells were mostly alphabeta T-cell receptor positive; however, a smaller influx of gammadelta T cells also took place. The number of resident dendritic cells increased markedly during infection, with numbers peaking around day 5 and remaining elevated 14 days later. The peak of the inflammatory response occurred on day 5 and declined thereafter, with the exception of dendritic cell and alphabeta T-cell numbers, which remained elevated. Starting around day 3, the tracheal epithelial cells expressed increasing levels of major histocompatibility complex class II antigen. This expression was maximal at day 5 and declined rapidly thereafter. In vitro culture of tracheal segments demonstrated that viral infection was not per se responsible for the upregulation of class II expression and that when cultured in the presence of gamma interferon, class II antigen was induced on epithelial cells.

Evidence for the early recruitment of T-cell receptor gamma delta+ T cells during rat listeriosis

We have previously reported that heat-shock protein (hsp) 60-reactive T-cell receptor (TCR)gamma delta+ T cells appear in the peritoneal cavity during the early stage of infection with Listeria monocytogenes in mice. In this study, we examined the kinetics of TCR gamma delta+ T cells during listeriosis in F344 rats by flow cytometry using a V65 monoclonal antibody (mAb) directed to a constant determinant of rat TCR gamma delta chains. TCR gamma delta+ T cells significantly increased in the peritoneal cavity on day 6 and then decreased by day 10 after infection, in parallel with the kinetics of hsp60 expression in the peritoneal macrophages during listeriosis in F344 rats. Most of the early appearing TCR gamma delta+ T cells were of the CD4- CD8 alpha beta+ CD5+ lymphocyte function-associated antigen (LFA)-1 alpha high CD45RC- interleukin-2 receptor (IL-2R) alpha- phenotype, although a significant fraction of the TCR gamma delta+ T cells expressed CD8 alpha only. The increase in TCR gamma delta+ T cells during listeriosis was prominent in F1 (F344 x Lewis) rats but only marginal in Lewis rats, which was correlated with the expression level of hsp 60 in the peritoneal macrophages. The peritoneal TCR gamma delta+ T cells in naive F344 rats appeared to proliferate significantly in response to recombinant hsp 60 (rhsp 60) derived from Mycobacterium bovis bacillus Calmette-Guérin (BCG). These results imply that the early appearance of hsp 60-reactive TCR gamma delta+ T cells during listerial infection can be generalized across species.

A protective role of gamma delta T cells in primary infection with Listeria monocytogenes in autoimmune non-obese diabetic mice

We investigated the host defense mechanism in primary infection with Listeria monocytogenes in non-obese diabetic (NOD) mice at pre-diabetic stage showing an impaired responsiveness of the alpha beta T cells to T-cell receptor (TCR) triggering. The NOD mice showed a deteriorated resistance at the late stage after an intraperitoneal infection with L. monocytogenes compared with BALB/c and C57BL/6 mice as assessed by bacterial growth in organs. Consistent with our previous findings, a prominent increase in number of gamma delta T cells was evident at the early stage after infection, while generation of Listeria-specific alpha beta T cells was impaired in these mice. In vivo administration of anti-TCR gamma delta monoclonal antibody (mAb) allowed L. monocytogenes to grow exaggeratedly in the NOD mice. These results imply that gamma delta T cells may be mainly involved in protection against primary infection with L. monocytogenes in NOD mice.