Depression of human neutrophil motility by influenza virus in vitro

Differential Ability of Pandemic and Seasonal H1N1 Influenza A Viruses To Alter the Function of Human Neutrophils

A long-standing notion is that IAV inhibits normal neutrophil function and thereby predisposes individuals to secondary bacterial infections. Here we report that seasonal H1N1 IAV primes human neutrophils for enhanced killing of Staphylococcus aureus. Moreover, we provide a comprehensive view of the changes in neutrophil gene expression during interaction with seasonal or pandemic IAV and report how these changes relate to functions such as bactericidal activity. This study expands our knowledge of IAV interactions with human neutrophils.

Neutrophils are essential cells of host innate immunity. Although the role of neutrophils in defense against bacterial and fungal infections is well characterized, there is a relative paucity of information about their role against viral infections. Influenza A virus (IAV) infection can be associated with secondary bacterial coinfection, and it has long been posited that the ability of IAV to alter normal neutrophil function predisposes individuals to secondary bacterial infections. To better understand this phenomenon, we evaluated the interaction of pandemic or seasonal H1N1 IAV with human neutrophils isolated from healthy persons. These viruses were ingested by human neutrophils and elicited changes in neutrophil gene expression that are consistent with an interferon-mediated immune response. The viability of neutrophils following coculture with either pandemic or seasonal H1N1 IAV was similar for up to 18 h of culture. Notably, neutrophil exposure to seasonal (but not pandemic) IAV primed these leukocytes for enhanced functions, including production of reactive oxygen species and bactericidal activity. Taken together, our results are at variance with the universal idea that IAV impairs neutrophil function directly to predispose individuals to secondary bacterial infections. Rather, we suggest that some strains of IAV prime neutrophils for enhanced bacterial clearance.

IMPORTANCE A long-standing notion is that IAV inhibits normal neutrophil function and thereby predisposes individuals to secondary bacterial infections. Here we report that seasonal H1N1 IAV primes human neutrophils for enhanced killing of Staphylococcus aureus. Moreover, we provide a comprehensive view of the changes in neutrophil gene expression during interaction with seasonal or pandemic IAV and report how these changes relate to functions such as bactericidal activity. This study expands our knowledge of IAV interactions with human neutrophils.

Vaccination against the M protein of Streptococcus pyogenes prevents death after influenza virus: S. pyogenes super-infection

Influenza virus infections are associated with a significant number of illnesses and deaths on an annual basis. Many of the deaths are due to complications from secondary bacterial invaders, including Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, and Streptococcus pyogenes. The β-hemolytic bacteria S. pyogenes colonizes both skin and respiratory surfaces, and frequently presents clinically as strep throat or impetigo. However, when these bacteria gain access to normally sterile sites, they can cause deadly diseases including sepsis, necrotizing fasciitis, and pneumonia. We previously developed a model of influenza virus:S. pyogenes super-infection, which we used to demonstrate that vaccination against influenza virus can limit deaths associated with a secondary bacterial infection, but this protection was not complete. In the current study, we evaluated the efficacy of a vaccine that targets the M protein of S. pyogenes to determine whether immunity toward the bacteria alone would allow the host to survive an influenza virus:S. pyogenes super-infection. Our data demonstrate that vaccination against the M protein induces IgG antibodies, in particular those of the IgG1 and IgG2a isotypes, and that these antibodies can interact with macrophages. Ultimately, this vaccine-induced immunity eliminated death within our influenza virus:S. pyogenes super-infection model, despite the fact that all M protein-vaccinated mice showed signs of illness following influenza virus inoculation. These findings identify immunity against bacteria as an important component of protection against influenza virus:bacteria super-infection.

Viral-bacterial interactions-therapeutic implications

Viral and bacterial respiratory tract infections are a leading cause of morbidity and mortality worldwide, despite the development of vaccines and potent antibiotics. Frequently, viruses and bacteria can co‐infect the same host, resulting in heightened pathology and severity of illness compared to single infections. Bacterial superinfections have been a significant cause of death during every influenza pandemic, including the 2009 H1N1 pandemic. This review will analyze the epidemiology and global impact of viral and bacterial co‐infections of the respiratory tract, with an emphasis on bacterial infections following influenza. We will next examine the mechanisms by which viral infections enhance the acquisition and severity of bacterial infections. Finally, we will discuss current management strategies for diagnosing and treating patients with suspected or confirmed viral‐bacterial infections of the respiratory tract. Further investigation into the interactions between viral and bacterial infections is necessary for developing new therapeutic approaches aimed at mitigating the severity of co‐infections.

Bench-to-bedside review: bacterial pneumonia with influenza - pathogenesis and clinical implications

Seasonal and pandemic influenza are frequently complicated by bacterial infections, causing additional hospitalization and mortality. Secondary bacterial respiratory infection can be subdivided into combined viral/bacterial pneumonia and post-influenza pneumonia, which differ in their pathogenesis. During combined viral/bacterial infection, the virus, the bacterium and the host interact with each other. Post-influenza pneumonia may, at least in part, be due to resolution of inflammation caused by the primary viral infection. These mechanisms restore tissue homeostasis but greatly impair the host response against unrelated bacterial pathogens. In this review we summarize the underlying mechanisms leading to combined viral/bacterial infection or post-influenza pneumonia and highlight important considerations for effective treatment of bacterial pneumonia during and shortly after influenza.

Depression of rat neutrophil exudation and motility by influenza virus

Purified influenza A and B viruses (3000 HA units) were injected intraperitoneally into rats. 1 h later the animals were given starch solution intraperitoneally, after which the number and composition of the exuded cells were determined at intervals. Both influenza A and B viruses depressed neutrophil exudation into the peritoneal cavity for a period of 10 to 17 h after the starch injection. The exudation of leukocytes other than neutrophils (a mixture of mononuclear cells and 5% to 10% eosinophils) was depressed for 17 h after starch injection by influenza A virus. When tested in vitro by a modification of the Boyden method, the peritoneal exudate neutrophils from virus-treated animals exhibited significantly depressed chemotaxis and consistently, although not always significantly, reduced chemokinesis (migration in the presence of a chemoattractant without a gradient) and random locomotion. Both influenza A and B viruses inhibited in vitro the motility of starch-induced peritoneal exudate neutrophils in Boyden chambers after a virus-cell interaction of 60 min at 37 degrees C. The present findings support the concept that impaired neutrophil exudation caused by depressed motility is one mechanism responsible for the increased susceptibility to bacterial superinfection during influenza.

Detection of influenza virus induced DNA damage by comet assay

Influenza virus A2/HK/68 is known to be a biological mutagen and teratogen. Reports are available implicating influenza virus as a causative agent of chromosomal aberrations in cells in culture and also in circulating leukocytes of humans. Also, an increased incidence of abortions, prenatal mortality and congenital abnormalities during the periods of epidemics has also been reported. In view of these reports, it would be worthwhile to screen persons especially pregnant women exposed to influenza virus for possible DNA damage. The present study reports the use of Comet assay to measure influenza virus induced DNA damage. We have carried out in vitro infection experiments using human leukocytes. Our results clearly indicate that influenza virus A2/HK/68 induces DNA damage in leukocytes right from 2-h post-infection. Maximum damage was observed at 24-h post-infection. However, at 48-h post-infection, a slight decrease was observed which can be attributed to the DNA repair occurring in the cells. Thereafter, irreparable damage was noticed. Cell viability results have shown lack of cytotoxicity till 72-h post-infection. However, significant cytotoxicity was observed only at 96-h post-infection. The occurrence of DNA damage without cell death may result in chromosomal aberrations or mutations. Therefore, it is most advisable to get screened for the possible DNA damage especially persons frequently infected with influenza and pregnant women.

Effects of middle ear effusion on neutrophil function

The neutrophil chemotactic activity of middle ear effusions (MEE) was measured in patients with pediatric chronic, adult chronic, and acute otitis media with effusion (OME). Chemotactic activity differed significantly among the three groups of otitis media in the following order: adult chronic less than pediatric chronic less than acute. Culture-positive effusions had higher chemotactic activity than did those that tested culture negative, suggesting that bacterial infection is related to neutrophil chemotactic activity. The chemotactic function of normal peripheral neutrophils was not enhanced by preincubation with MEE, but their bactericidal function was enhanced. In conclusion, bacterial infection in the middle ear is one of the major determining factors of neutrophil infiltration during OME, and MEE enhances the bactericidal function of neutrophils.

Synthesis of viral proteins in polymorphonuclear leukocytes infected with influenza A virus

Various reports have indicated that infection of polymorphonuclear leukocytes (PMNL) with influenza virus causes depression of their metabolic and chemotactic responses, but the effect the PMNL has on the life cycle of influenza virus has not been well defined. The studies reported here were undertaken to determine whether influenza virus could replicate within PMNL. Virus-infected and uninfected PMNL were labeled with [35S]methionine and analyzed by gel electrophoresis and fluorography for detection of newly synthesized proteins. Both host- and virus-specific proteins were produced within PMNL. By using indirect immunofluorescence techniques combined with flow cytometry, the expression of newly synthesized viral antigens was detected in virus-infected PMNL. Plaque assays on supernatant fluid from infected PMNL showed that infectious progeny were not produced, indicating that influenza virus infection of PMNL is abortive.

Viral-bacterial synergistic interaction in respiratory disease

In the present review we have identified how viruses can alter the host's susceptibility to bacterial infections by altering both environmental conditions in the lung which favor bacterial replication as well as by suppressing the host's defense mechanisms which prevent clearance of the bacteria. In many instances, these interactions are extremely complex but similar for many viruses. If the virus can overcome the initial host defense mechanisms, which include local antibody and mucus, the virus initiates tissue damage as a result of direct replication within the epithelial cells lining the mucosal surfaces of the respiratory tract. As a result of virus infection, the host cells respond by producing a variety of mediators including various types of interferons, which can alter both virus replication and host response. Replication also produces by-products of virus infection capable of initiating an inflammatory process, which in turn, through release of other mediators, can further modify lung defense mechanisms and encourage bacterial adherence and growth. The bacterium, in turn, releases chemotactic factors which encourage infiltration of specific effector cells into the lung. These effector cells can cause tissue damage and immunopathology, which encourage rapid bacterial growth and may result in death of the animal. In order to be able to control this complicated scenario, it is important either to prevent the initial infection with viruses or to reduce the degree of immunosuppression, so that bacterial clearance can occur rapidly before microcolony formation and extensive lung damage occur. Once a large amount of bacterial replication and lung damage is present, the use of antibiotics is generally of limited value. A schematic illustration of the complexity of the various interactions and counteractions occurring during virus--bacterial synergistic interactions is presented in Fig. 1.

Neuraminidase activity is not the cause of influenza virus-induced neutrophil dysfunction

Influenza viruses have been shown to decrease the ability of polymorphonuclear leukocytes (PMN) to respond to a variety of stimuli. This study was done to determine if viral neuraminidase was responsible for decreased PMN function. Treatment of human PMN with purified neuraminidases from influenza virus, Vibrio cholerae, or Clostridium perfringens did not significantly affect the ability of human PMN to respond to stimulation. Occasional virus preparations that lacked the ability to depress PMN function did not differ in neuraminidase activity from viruses capable of causing depression. These results demonstrate that neuraminidase activity is not the cause of influenza virus-induced PMN dysfunction.

Different virulence of influenza A virus strains and susceptibility to pneumococcal otitis media in chinchillas

We have previously shown that chinchillas infected with a multiply passaged laboratory strain of influenza A/NWS/33 (H1N1) develop negative middle-ear pressure; polymorphonuclear leukocyte oxidative, bactericidal, and chemotactic dysfunction; and increased susceptibility to pneumococcal otitis media. Because influenza A virus strains show different virulence in humans, three such strains were compared in the chinchilla model. Negative middle-ear pressure and tympanic membrane inflammation developed significantly more often in chinchillas infected with wild-type H3N2 virus than with either wild-type H1N1 virus or an attenuated, cold-adapted H3N2 vaccine strain, CR29. Marked depression in polymorphonuclear leukocyte chemiluminescent activity also developed significantly more often in H3N2 infected animals than in H1N1- or CR29-infected animals. Intranasal challenge of influenza virus-infected animals with type 7 Streptococcus pneumoniae resulted in a significantly greater occurrence of pneumococcal otitis media in H3N2-infected animals than in H1N1-, CR29-, or non-influenza-infected control animals. Clearance of pneumococci from nasal washings of animals infected with wild-type H3N2 was significantly delayed in comparison with the other groups. Thus, the previously demonstrated increased susceptibility to otitis media among children infected with H3N2 influenza virus may relate to the capacity of this strain to induce negative middle-ear pressure, polymorphonuclear leukocyte dysfunction, and alteration in the mucosal clearance of pneumococci.

Acquired chemotactic inhibitors during infection with guinea pig cytomegalovirus

Factors involved in neutrophil and monocyte migrations were serially studied in strain 2 guinea pigs undergoing initial cytomegalovirus infection and sham-inoculated controls. All studies remained unchanged in uninfected animals. Monocyte migrations and neutrophil spontaneous migration remained unchanged in infected animals. However, transient abnormalities occurred early in infection, comprising a decrease in neutrophil-directed migration towards C5-derived chemotactic fractions (C5-fr) and a decrease in the chemotactic activity of zymosan-activated plasma. Consequently, the presence of neutrophil- and chemotaxin-directed inhibitors in plasma was investigated. Normal neutrophils, C5-fr, Escherichia coli-derived bacterial factor, and the synthetic peptide F-met-leu-phe were first incubated with control or infected plasmas and then assayed for directed migration and lysosomal enzyme release. Results indicated the de novo appearance of both neutrophil- and chemotaxin-directed inhibitory activities in plasma during early infection. The neutrophil-directed inhibition was heat stable (56 degrees C for 120 min) and nonspecific (responses to all chemotaxins were inhibited). The chemotaxin-directed inhibition was heat stable and C5-fr specific. The cytomegalovirus-induced inhibitors may be important in the enhanced susceptibility to concurrent opportunistic infections.

Effect of influenza virus on phagocytic cells

Many viral infections predispose to bacterial superinfection, and it has been suggested that the increased susceptibility to bacterial infections is at least in part due to the effect of virus on the phagocytic cell function. Since the mechanisms by which the viruses affect neutrophil function are not well understood, we studied the function of polymorphonuclear leukocytes (PMNs) after incubation with influenza virus. Phagocytosis was assayed by incubating influenza virus (strain type A-Texas-77 [H2N2] ) treated leukocytes with 3H-thymidine-labelled staphylococci. The oxidative metabolism of the PMNs was studied by measuring the chemiluminescence generated by virus-treated PMNs after incubation with zymosan. Chemotaxis was measured under agarose. After incubation with 10(7) EID50 units of influenza virus, PMNs ingested only 35% of the bacteria, whereas control leukocytes ingested over 80%. Influenza virus also reduced the mobility of the PMNs and markedly suppressed the generation of chemiluminiscence. UV-killed virus with intact neuraminidase produced similar effects but virus with heat-inactivated neuraminidase did not. Virus envelope-neuraminidase may be responsible for some of the effects of the virus on the PMNs.

Influenza A virus-induced polymorphonuclear leukocyte dysfunction in the pathogenesis of experimental pneumococcal otitis media

The role of influenza A virus-induced polymorphonuclear leukocyte and eustachian tube dysfunction in the pathogenesis of acute purulent otitis media was studied in chinchillas. Polymorphonuclear leukocyte function, middle ear pressure, and the incidence of pneumococcal otitis media were observed after intranasal inoculation with influenza A virus, Streptococcus pneumoniae, or both. Results showed that depressed negative middle ear pressure and polymorphonuclear leukocyte chemiluminescence and chemotactic activity occurred after influenza inoculation, but not after inoculation with pneumococcus alone. The greatest incidence of pneumococcal otitis media occurred when the pneumococcus was inoculated just before the time of influenza-induced polymorphonuclear leukocyte dysfunction and negative middle ear pressure. Animals that had unilateral tympanostomy tubes placed before inoculation of influenza with pneumococcus showed no difference in the occurrence of pneumococcal otitis media in ventilated and nonventilated ears, suggesting that polymorphonuclear leukocyte dysfunction contributes more to the pathogenesis of pneumococcal otitis media than does negative middle ear pressure in this animal model.

Depression of monocyte and polymorphonuclear leukocyte oxidative metabolism and bactericidal capacity by influenza A virus

Decreased host defense against bacterial disease associated with influenza infection may be related to virus-induced changes in phagocytic cell function. Influenza A virus initiates the respiratory burst in peripheral blood monocytes and polymorphonuclear leukocytes, with a peak chemiluminescent response approximately 3 min after virus is added to the cells in vitro. Electron micrographs of phagocytic cells incubated with influenza virus demonstrated virus attached to the cell membrane and within phagocytic vacuoles. After 20 min of incubation of the virus with phagocytic cells, the chemiluminescent response to opsonized zymosan or phorbol myristate acetate was decreased by 30 to 90%. Phagocytic activity of monocytes and polymorphonuclear leukocytes incubate with influenza virus was normal, but the bactericidal activity was significantly depressed. Influenza A virus therefore stimulates an oxidative burst in monocytes as well as polymorphonuclear leukocytes, leading to a subsequent depression of the oxidative metabolic response and bactericidal capacity of the phagocytic cells.

Initiation of the respiratory burst of human neutrophils by influenza virus

The role of the oxygen-dependent microbicidal systems of polymorphonuclear neutrophils in virus inactivation is not known. We found that isolated neutrophils responded to incubation with purified influenza virus A particles by consumption of oxygen, generation of chemiluminescence, and production of superoxide; these reactions occurred in the absence of serum. Resting leukocyte oxygen consumption doubled in the presence of virus; the average rate of consumption 2 to 12 min after virus was added was 1.54 nmol/10(7) cells per min. Live virus also stimulated superoxide production in a dose-dependent manner at a rate up to 4.54 nmol/10(7) cells per min. Luminol-amplified chemiluminescence was a rapid dose-dependent reaction which peaked 2 to 4 min after live or ultraviolet light-inactivated virus was added. No light was emitted when heat-inactivated virus particles were used, suggesting that heat-labile factors on the virus envelope may be involved in oxidative stimulation. Virus-stimulated neutrophils from a patient with chronic granulomatous disease emitted no light. The evidence that virus initiated the respiratory burst of neutrophils provided a potential mechanism for virus destruction, either by direct intracellular inactivation or by neutrophil-mediated cellular cytotoxicity of virus-infected target cells.

Immobilization of viral and mycoplasma antigens and of immunoglobulins on polystyrene surface for immunoassays

The immobilization of purified influenza virus, rubella virus, crude nuclear cytomegalovirus antigen and of mycoplasma on polystyrene tubes was studied using radio-iodinated preparations. The antigen activities on tube surfaces were determined using sequentially specific human antibodies and alkaline phosphatase-conjugated anti-human IgG in an enzyme-immunoassay (EIA) reaction. In addition, immobilization of radio-iodinated human IgG, IgM, and IgA, serving as model proteins, was studied using the respective anti-immunoglobulin conjugates in EIA directly. Pretreatment of the surface with albumin and glutaraldehyde inhibited the adsorption and antigenicity of IgG. Increase of temperature and thus of speed of adsorption did not affect the fraction of antigen eluted during the test procedure. Only with IgG and IgA was it necessary to saturate the polystyrene surface in order to achieve maximal reactivity in EIA. With other antigens, maximal reactivity in EIA was obtained with amounts of protein much lower than the maximal amount that could be adsorbed per tube. IgM was found to have an exceptionally high affinity to polystyrene.

Neutrophil function in children with acute lymphoblastic leukaemia in the presence and absence of viral infections

Neutrophil function was assessed regularly in 26 children with acute lymphoblastic leukaemia (ALL) in remission, both when they were well and during viral infections. Tests of candidacidal ability when these children were apparently free of infection showed a trend towards lower levels compared with controls. The most pronounced depression of candidacidal ability and chemotaxis was during viral infections, and these two functions of neutrophils were more likely to be abnormal then than when the children were free of infection. In children with ALL in remission, whose neutrophils may function abnormally even when they are well, the risk of acquiring bacterial or fungal infections may be made greater by virus infections.