Hypersensitivity pneumonitis: a complex lung disease

Abstract

Hypersensitivity pneumonitis (HP), also called extrinsic allergic alveolitis, is a respiratory syndrome involving the lung parenchyma and specifically the alveoli, terminal bronchioli, and alveolar interstitium, due to a delayed allergic reaction. Such reaction is secondary to a repeated and prolonged inhalation of different types of organic dusts or other substances to which the patient is sensitized and hyper responsive, primarily consisting of organic dusts of animal or vegetable origin, more rarely from chemicals. The prevalence of HP is difficult to evaluate because of uncertainties in detection and misdiagnosis and lacking of widely accepted diagnostic criteria, and varies considerably depending on disease definition, diagnostic methods, exposure modalities, geographical conditions, agricultural and industrial practices, and host risk factors. HP can be caused by multiple agents that are present in work places and in the home, such as microbes, animal and plant proteins, organic and inorganic chemicals. The number of environment, settings and causative agents is increasing over time. From the clinical point of view HP can be divided in acute/subacute and chronic, depending on the intensity and frequency of exposure to causative antigens. The mainstay in managing HP is the avoidance of the causative antigen, though the complete removal is not always possible due to the difficulties to identify the agent or because its avoidance may lead to major changes in life style or occupational settings. HP is a complex syndrome that needs urgently for more stringent and selective diagnostic criteria and validation, including wider panels of IgG, and a closer collaboration with occupational physicians, as part of a multidisciplinary expertise.

Case of summer-type hypersensitivity pneumonitis complicated with IgA nephropathy

“…Hypersensitive pneumonitis is a disease caused by type Ⅲ and IV hypersensitivity 1. Repeated exposure to airborne antigens induces formation of immune complexes with IgA and IgG, as well as complement activation 10. One of the most common pathogens causing summer-type HP in Japan is T. asahii 10…”

Sertraline-induced hypersensitivity pneumonitis

“…There are several non-specific pathways in which SSRIs can precipitate bronchioles and capillary alveoli injury by oxidation, cytotoxic mechanisms and immune-response mediation 11 12. Accumulation of medication may be due to genetic factors such as P450 cytochrome and Mucin-5B (MUC5B) promoter polymorphisms that may predispose an individual to lung parenchyma injury with SSRIs 12. However, MUC5B is not routinely analysed in practice.…”

Update of reference values for IgG antibodies against typical antigens of hypersensitivity pneumonitis

“…Hypersensitivity pneumonitis (HP), also known as extrinsic allergic alveolitis (EAA), is a respiratory syndrome involving the lung parenchyma and specifically the alveoli, terminal bronchioles, and alveolar interstitium, due to a delayed allergic reaction [1]. In several cases HP is associated with a repeated and prolonged inhalation of compounds with immunogenic properties and is accompanied by systemic manifestations (e.g.…”

“…fever and weight loss). Clinical presentation and disease progression can be extremely variable, depending on the nature of the causal agent, exposure duration, and intensity, as well as individual host factors [1]. The spectra of typical HP-inducing antigens are commonly classified into five broad categories: animal (especially avian antigens) proteins, plant proteins, fungi/yeasts, bacteria/mycobacteria and lowmolecular chemicals [2].…”