Infections in "noninfectious" lung diseases

Infectious Lung Diseases and Endogenous Oxidative Stress

Lower respiratory tract infections, according to the World Health Organization, account for nearly one third of all deaths from infectious diseases. They account for approximately 4 million deaths annually including children and adults and provide a greater disease burden than HIV and malaria. Among the common respiratory diseases, tuberculosis, influenza, and pneumonia are very common and can be life threatening if not treated properly. The causative agent of tuberculosis is the slow-growing bacilli Mycobacterium tuberculosis, while the causative agent of influenza is a segmented genome RNA virus. Pneumonia can be caused by a number of different microorganisms like bacteria, virus, and mycoplasma. In case of the entry of a pathogen in our body, the immune system gets activated, and the phagocytic cells try to eliminate it by generating reactive oxygen and nitrogen species (ROS and RNS) inside the phagosome. These reactive species or respiratory bursts are sufficient to eliminate most of the pathogens, except a few. M. tuberculosis is one such microorganism that has evolved mechanisms to escape this respiratory burst-mediated killing and thus survive and grow inside the macrophages. Infection with M. tuberculosis leads to the destruction of macrophages and release of cytokines, which lead to prolonged immune activation and oxidative stress. In some cases, the bacilli remain dormant inside macrophages for a long time. Flu viruses infect the epithelial cells present in respiratory tract, and the infection site is dependent on the hemagglutinin protein present on their capsid. Destruction of epithelial cells promotes secretion of mucus and activation of immune system leading to the oxidative damage. Community-acquired pneumonia is more serious and difficult to treat. In all these infections, ROS/RNS are developed as a defense mechanism against the pathogen. Persistence of the pathogen for a long time would lead to the uncontrolled production of ROS/RNS which will lead to oxidative stress and tissue damage to the host. Administration of antioxidants along with conventional treatments can be useful in the elimination of the reactive oxygen and nitrogen species.

The Saudi Thoracic Society guidelines for diagnosis and management of noncystic fibrosis bronchiectasis

This is the first guideline developed by the Saudi Thoracic Society for the diagnosis and management of noncystic fibrosis bronchiectasis. Local experts including pulmonologists, infectious disease specialists, thoracic surgeons, respiratory therapists, and others from adult and pediatric departments provided the best practice evidence recommendations based on the available international and local literature. The main objective of this guideline is to utilize the current published evidence to develop recommendations about management of bronchiectasis suitable to our local health-care system and available resources. We aim to provide clinicians with tools to standardize the diagnosis and management of bronchiectasis. This guideline targets primary care physicians, family medicine practitioners, practicing internists and respiratory physicians, and all other health-care providers involved in the care of the patients with bronchiectasis.

Resolvin D1 Dampens Pulmonary Inflammation and Promotes Clearance of Nontypeable Haemophilus influenzae

Nontypeable Haemophilus influenzae (NTHi) is a Gram-negative, opportunistic pathogen that frequently causes ear infections, bronchitis, pneumonia, and exacerbations in patients with underlying inflammatory diseases, such as chronic obstructive pulmonary disease. In mice, NTHi is rapidly cleared, but a strong inflammatory response persists, underscoring the concept that NTHi induces dysregulation of normal inflammatory responses and causes a failure to resolve. Lipid-derived specialized proresolving mediators (SPMs) play a critical role in the active resolution of inflammation by both suppressing proinflammatory actions and promoting resolution pathways. Importantly, SPMs lack the immunosuppressive properties of classical anti-inflammatory therapies. On the basis of these characteristics, we hypothesized that aspirin-triggered resolvin D1 (AT-RvD1) would dampen NTHi-induced inflammation while still enhancing bacterial clearance. C57BL/6 mice were treated with AT-RvD1 and infected with live NTHi. AT-RvD1-treated mice had lower total cell counts and neutrophils in bronchoalveolar lavage fluid, and had earlier influx of macrophages. In addition, AT-RvD1-treated mice showed changes in temporal regulation of inflammatory cytokines and enzymes, with decreased KC at 6 h and decreased IL-6, TNF-α, and cyclooxygenase-2 expression at 24 h post infection. Despite reduced inflammation, AT-RvD1-treated mice had reduced NTHi bacterial load, mediated by enhanced clearance by macrophages and a skewing toward an M2 phenotype. Finally, AT-RvD1 protected NTHi-infected mice from weight loss, hypothermia, hypoxemia, and respiratory compromise. This research highlights the beneficial role of SPMs in pulmonary bacterial infections and provides the groundwork for further investigation into SPMs as alternatives to immunosuppressive therapies like steroids.

The Lung Immune Response to Nontypeable Haemophilus influenzae (Lung Immunity to NTHi)

Haemophilus influenzae is divided into typeable or nontypeable strains based on the presence or absence of a polysaccharide capsule. The typeable strains (such as type b) are an important cause of systemic infection, whilst the nontypeable strains (designated as NTHi) are predominantly respiratory mucosal pathogens. NTHi is present as part of the normal microbiome in the nasopharynx, from where it may spread down to the lower respiratory tract. In this context it is no longer a commensal and becomes an important respiratory pathogen associated with a range of common conditions including bronchitis, bronchiectasis, pneumonia, and particularly chronic obstructive pulmonary disease. NTHi induces a strong inflammatory response in the respiratory tract with activation of immune responses, which often fail to clear the bacteria from the lung. This results in recurrent/persistent infection and chronic inflammation with consequent lung pathology. This review will summarise the current literature about the lung immune response to nontypeable Haemophilus influenzae, a topic that has important implications for patient management.

The lung mycobiome: an emerging field of the human respiratory microbiome

The lung microbiome, which is believed to be stable or at least transient in healthy people, is now considered as a poly-microorganism component contributing to disease pathogenesis. Most research studies on the respiratory microbiome have focused on bacteria and their impact on lung health, but there is evidence that other non-bacterial organisms, comprising the viruses (virome) and fungi (mycobiome), are also likely to play an important role in healthy people as well as in patients. In the last few years, the lung mycobiome (previously named the fungal microbiota or microbiome) has drawn closer attention. There is growing evidence that the lung mycobiome has a significant impact on clinical outcome of chronic respiratory diseases (CRD) such as asthma, chronic obstructive pulmonary disease, cystic fibrosis, and bronchiectasis. Thanks to advances in culture independent methods, especially next generation sequencing, a number of fungi not detected by culture methods have been molecularly identified in human lungs. It has been shown that the structure and diversity of the lung mycobiome vary in different populations (healthy and different diseased individuals) which could play a role in CRD. Moreover, the link between lung mycobiome and different biomes of other body sites, especially the gut, has also been unraveled. By interacting with the bacteriome and/or virome, the respiratory mycobiome appears to be a cofactor in inflammation and in the host immune response, and therefore may contribute to the decline of the lung function and the disease progression. In this review, we report the recent limited explorations of the human respiratory mycobiome, and discuss the mycobiome’s connections with other local microbial communities, as well as the relationships with the different biomes of other body sites. These studies suggest several outlooks for this understudied emerging field, which will certainly call for a renewal of our understanding of pulmonary diseases.