Effect of influenza virus on phagocytic cells

Virus-Induced Changes of the Respiratory Tract Environment Promote Secondary Infections With Streptococcus pneumoniae

Secondary bacterial infections enhance the disease burden of influenza infections substantially. Streptococcus pneumoniae (the pneumococcus) plays a major role in the synergism between bacterial and viral pathogens, which is based on complex interactions between the pathogen and the host immune response. Here, we discuss mechanisms that drive the pathogenesis of a secondary pneumococcal infection after an influenza infection with a focus on how pneumococci senses and adapts to the influenza-modified environment. We briefly summarize what is known regarding secondary bacterial infection in relation to COVID-19 and highlight the need to improve our current strategies to prevent and treat viral bacterial coinfections.

Avian Respiratory Coinfection and Impact on Avian Influenza Pathogenicity in Domestic Poultry: Field and Experimental Findings

The avian respiratory system hosts a wide range of commensal and potential pathogenic bacteria and/or viruses that interact with each other. Such interactions could be either synergistic or antagonistic, which subsequently determines the severity of the disease complex. The intensive rearing methods of poultry are responsible for the marked increase in avian respiratory diseases worldwide. The interaction between avian influenza with other pathogens can guarantee the continuous existence of other avian pathogens, which represents a global concern. A better understanding of the impact of the interaction between avian influenza virus and other avian respiratory pathogens provides a better insight into the respiratory disease complex in poultry and can lead to improved intervention strategies aimed at controlling virus spread.

K63-Linked Polyubiquitination on TRAF6 Regulates LPS-Mediated MAPK Activation, Cytokine Production, and Bacterial Clearance in Toll-Like Receptor 7/8 Primed Murine Macrophages

Post viral infection bacterial pneumonia is a major cause of morbidity and mortality associated with both seasonal and pandemic influenza virus illness. Despite much efforts put into the discovery of mechanisms of post viral-bacterial infections and their complications in recent years, the molecular mechanisms underlying the increased susceptibility to bacterial infection remain poorly understood. In this study, we focused on the pathways regulating immune responses in murine macrophages and modeled post viral-bacterial infections through pretreatment of bone marrow-derived macrophages (BMDMs) with a toll-like receptor (TLR) 7/8 ligand (R848) and subsequent challenge with TLR2/4 agonists to mimic bacterial infection. We found R848-primed BMDMs upon subsequent exposure to TLR2/4 ligands respond with enhanced inflammatory cytokine production, especially IL-6 and TNF-α. The enhanced cytokine production in R848-primed BMDMs in response to TLR2/4 was due to increased TGF-β-activated kinase (TAK) 1 phosphorylation with subsequent activation of ERK and p38 MAPKs. Furthermore, we identified that R848 priming leads to increased K63-linked polyubiquitination on TRAF6. K63-linked polyubiquitination on TRAF6 is a signal leading to enhanced activation of downstream pathways including TAK1. Importantly, R848-primed BMDMs infected with live bacteria exhibited decreased bacterial clearance. Small-molecule enhancer of rapamycin 3, an ubiquitin ligase inhibitor reversed the K63-linked polyubiquitination on TRAF6 in R848-primed BMDMs and subsequently decreased TAK1 and MAPK phosphorylation, and cytokine production as well as reversed the decreased bacterial clearance capacity of BMDMs. Our study may provide a novel molecular target to alleviate post viral-bacterial infections.

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.

Phage-Phagocyte Interactions and Their Implications for Phage Application as Therapeutics

Phagocytes are the main component of innate immunity. They remove pathogens and particles from organisms using their bactericidal tools in the form of both reactive oxygen species and degrading enzymes-contained in granules-that are potentially toxic proteins. Therefore, it is important to investigate the possible interactions between phages and immune cells and avoid any phage side effects on them. Recent progress in knowledge concerning the influence of phages on phagocytes is also important as such interactions may shape the immune response. In this review we have summarized the current knowledge on phage interactions with phagocytes described so far and their potential implications for phage therapy. The data suggesting that phage do not downregulate important phagocyte functions are especially relevant for the concept of phage therapy.

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.

Cell surface expression of FcγRI (CD64) on neutrophils and monocytes in patients with influenza A, with and without complications

The expression of the Fcgamma-receptor I (FcgammaRI), CD64 on normal neutrophils is up-regulated during bacterial infections. CD64 is a promising diagnostic tool in the diagnosis of acute infections. The aim was to study surface expressions of CD64 on neutrophils and monocytes in patients with influenza A with and without complications and evaluate these as diagnostic tools in comparison with serum levels of HNL (human neutrophil lipocalin). CD64 expression on neutrophils and monocytes was evaluated by flow cytometry. HNL was assayed by a specific radioimmunoassay. 22 patients with influenza A with or without complications were included and the results compared with those of 29 patients with acute bacterial infections and 29 healthy subjects. Neutrophil expression of CD64 was increased in influenza A with raised proportion expressing CD64 in complicated compared to uncomplicated influenza. The expression was significantly higher in bacterial infections compared to both influenza groups. Serum levels of HNL were raised in all infection groups, but significantly more so in the group with bacterial infection. ROC-curve analysis showed that neutrophil expression of CD64 and the serum levels of HNL had similar diagnostic power in the discrimination between acute bacterial infections and influenza A. Monocyte expression of CD64 was raised in all infections with no differences between subgroups. We conclude that neutrophil expression of CD64 and serum levels of HNL are both promising assays in the distinction between infections caused by bacteria or influenza A, whereas CD64 could identify patients with complications of their influenza A infection.

Neutrophil and monocyte receptor expression in uncomplicated and complicated influenza A infection with pneumonia

Following influenza, the elderly and those with chronic heart/lung diseases are often affected by bacterial complications such as pneumonia. Whether neutrophil and monocyte functions are affected differently in patients with or without complications is less well known. Therefore, blood neutrophil and monocyte surface receptor expressions were measured in patients with influenza A, with or without complications, by means of flow cytometry. Neutrophil expressions of the adhesion molecules CD11b and CD66b were increased in influenza A, with the highest expression of CD11b in uncomplicated influenza. Monocyte expressions of CD11b and CD18 were also higher in influenza compared with bacterial infection and healthy controls. Neutrophil expressions of the phagocyte receptors CD64 and CD32 and the complement receptor CD35 were impaired in influenza with and without pneumonia compared with bacterial infection, whereas the expressions in monocytes were increased in all infected groups. The expression of the phagocyte receptor CD16 on neutrophils was impaired in all infected groups. Our results suggest increased recruitment of neutrophils and monocytes to infected areas by up-regulation of adhesion molecules in influenza that may be involved in the inflammatory response during infection. In contrast, depression of phagocyte receptor expression on neutrophils in patients with influenza pneumonia may contribute to increased susceptibility to bacterial infections and impaired clearance of encapsulated bacteria such as pneumococci.

Increased incidence of menstruation-associated bactericidal defects in neutrophils from women who have recovered from toxic shock syndrome

There is a growing suspicion that a host abnormality may contribute to the pathogenesis of toxic shock syndrome (TSS). We found that females (5 of 5) who had recovered from TSS had transient, menstruation-associated decreases (greater than or equal to 9%) in the ability of their neutrophils to kill Staphylococcus aureus. 502A in vitro more often (P = 0.040 by Fisher's exact test) than non-TSS-affected control subjects (5 of 12). In addition, the average decrease in bactericidal activity in neutrophils obtained during menstruation from recovered TSS patients was 30 +/- 9% compared to 7 +/- 7% for neutrophils from non-TSS-affected control subjects. The results are consistent with the possibility that transient menstruation-associated decreases in neutrophil bactericidal function may indicate susceptibility and/or contribute to the development of TSS.

The effect of parainfluenza virus type 3 and Pasteurella haemolytica on oxygen-dependent and oxygen-independent bactericidal mechanisms of ovine pulmonary phagocytic cells

Groups of caesarean-derived, colostrum-deprived lambs were inoculated by the intratracheal route with Pasteurella haemolytica, either alone or 4 or 6 days after the inoculation of parainfluenza virus type 3 (PI3). Other groups were inoculated with PI3 followed by veal infusion broth, or with uninfected cell culture fluid followed by veal infusion broth (controls). All lambs were killed 24 h after the second inoculation. Pulmonary phagocytic cells were recovered by lavage and separated into alveolar macrophage (AM) and neutrophil fractions by density gradient centrifugation. Bacterial proliferation was detected in the lungs of all five lambs inoculated with P. haemolytica 6 days after PI3 but in only one of five inoculated with P. haemolytica 4 days after PI3 and one of five inoculated with P. haemolytica alone. The number of phagocytic cells recovered from the lungs was highest in animals inoculated with P. haemolytica 6 days after PI3 and, overall, a greater number of both AM and neutrophils was recovered from the lungs of animals where bacterial proliferation occurred (greater than 10(5.0) P. haemolytica 100 g-1 lung) than from those that controlled the bacterial infection. Oxygen-dependent bactericidal activity of AM and neutrophils was measured by chemiluminescence. Infection with PI3 and P. haemolytica increased the chemiluminescence responses. The highest responses were recorded from lambs inoculated with P. haemolytica 6 days after PI3, the group where pulmonary clearance was poorest. Overall, responses were higher in lambs in which bacterial proliferation occurred than in those that controlled the infection. On the other hand, oxygen-independent bactericidal activity, measured by the direct effects of neutrophil lysates on Escherichia coli, was lowest in lambs inoculated with P. haemolytica 6 days after PI3 and was lower in lambs where bacterial proliferation occurred.

Modulation of phagocytic cell function

Phagocytosis is an important factor in the defense of the host against all kinds of microorganisms. The process of phagocytosis of microorganisms by phagocytes can be separated into distinct but interrelated phases: adherence, chemotaxis, opsonization, attachment, ingestion, degranulation and killing. Phagocytosis is accompanied by an increase in oxygen metabolism in which H2O2 and activated oxygen species are generated. Modulation of phagocytic cell function can be brought about by a variety of substances. Microorganisms produce and contain components which influence the process of phagocytosis. Surrounding tissue cells and the phagocytes themselves produce biologically active molecules that modulate phagocytosis.

The effect of parainfluenza virus type 3 on the phagocytic cell response of the ovine lung to Pasteurella haemolytica

Groups of Caesarean-derived, colostrum-deprived lambs were inoculated by the intratracheal route with Pasteurella haemolytica 4 to 6 days after the inoculation of parainfluenza virus type 3 (PI3). Some were killed immediately (0 h) and others 24 h later. Control groups were inoculated with PI3 alone, P. haemolytica alone or media alone. Pulmonary phagocytic cells, P. haemolytica and PI3 were recovered by pulmonary lavage. The phagocytes were separated into alveolar macrophage (AM) and neutrophil fractions by density gradient centrifugation and examined biochemically and microbiologically. Twenty-four hours after the inoculation of P. haemolytica bacterial proliferation to greater than 0 h levels had occurred in four of six animals inoculated with P. haemolytica alone, two of eight inoculated with P. haemolytica 4 days after PI3 and all of eight inoculated with P. haemolytica 6 days after PI3. Mean bacterial numbers in animals inoculated with P. haemolytica 6 days after PI3 and killed at 24 h (10(9.1 +/- 1.9)) were significantly higher than they were in the other two groups killed at this time (PI3 4 days, P. haemolytica 24 h, mean = 10(5.3 +/- 1.7); P. haemolytica alone 24 h, mean = 10(4.5 +/- 2.9)). Pneumonic lesions were also more severe in the first group. This defect in pulmonary clearance and increase in the severity of pneumonia in animals inoculated with P. haemolytica 6 days after PI3 coincided with a 1000-fold decrease in virus titres in the lung between Day 6 and Day 7 after virus inoculation and the first detectable evidence of the host's immune response. The virus infection resulted in a significant increase in the number of AM that could be recovered from the lung and an increase in the number of AM with cytoplasmic vacuolation. However, there was no difference in the total number of AM or the number of vacuolated AM between animals that controlled the P. haemolytica infection and those in which proliferation of P. haemolytica occurred. The inoculation of P. haemolytica resulted in a 100-fold increase in the number of neutrophils in the lavage fluid, but there were no differences between virus-infected and uninfected animals, nor was there a difference between animals that controlled the P. haemolytica infection and those that did not.(ABSTRACT TRUNCATED AT 400 WORDS)

Interactions between human polymorphonuclear leukocytes and influenza virus

The effects of influenza virus A (H3N2) on several functions of human polymorphonuclear leukocytes (PMN) were examined. Incubation of PMN with virus induced chemiluminescence, aggregation, and degranulation of the leukocytes. The amount of chemiluminescence generated increased from 1 X 10(6) to 6 X 10(6) cpm when 2.5 X 10(6) to 2 X 10(7) virus particles were added to 2.5 X 10(6) PMN. Maximal aggregation occurred within 2 min and the response depended on the amount of virus added to the PMN. Release of acid phosphatase by virus-treated PMN was 62 +/- 12% within 1 h compared with 7 +/- 7% by control PMN (P less than 0.005). Incubation of PMN with influenza virus resulted in a diminished phagocytic activity of the phagocytes. PMN from a patient with chronic granulomatous disease were similarly affected. It was thus concluded that the observed defect in phagocytic activity was not due to the reactive oxygen species generated by the PMN during incubation with virus.