Pulmonary infections in transplantation pathology

Lung Transplantation

The therapeutic options for patients with advanced pulmonary parenchymal or vascular disorders are currently limited. Lung transplantation remains one of the few viable interventions, but on account of the insufficient donor pool only a minority of these patients actually undergo the procedure each year. Following transplantation there are a number of early and late allograft complications such as primary graft dysfunction, allograft rejection, infection, post-transplant lymphoproliferative disorder and late injury that is now classified as chronic lung allograft dysfunction. The pathologist plays an essential role in the diagnosis and classification of these myriad complications. Although the transplant procedures are performed in selected centers patients typically return to their local centers. When complications arise it is often the responsibility of the local pathologist to evaluate specimens. Therefore familiarity with the pathology of lung transplantation is important.

[Pulmonary infections following solid organ transplantation]

Solid organ transplantation is the standard of care for selected patients with severe vital organ dysfunction. The need for immunosuppression to prevent organ rejection is a common characteristic of recipients. Immunosuppression increases the risk of infections, especially with low virulence opportunistic pathogens. Infections following solid organ transplantation mainly affect the lungs and the airways. Establishing the diagnosis includes a wide spectrum of pulmonary diagnostics, high standard microbiological analysis and various imaging methods. With the improvement of treatment options, the number of kidney, liver, heart and lung transplant recipients is increasing and, therefore, more and more physicians may meet pulmonary complications in these patients.

[Immunodeficiency and immunocompromised patients. Opportunistic infection of the lungs]

The number of patients suffering from innate, acquired or iatrogenic immunodeficiency is constantly rising. Thus the number of clinically relevant infections caused by rare or unusual pathogens is also increasing. Histopathological investigations allow the identification of difficult to culture infectious agents as well as the differentiation of tissue invasive infections from superficial colonization. In this review morphological reaction patterns and their differential diagnoses of the most common bacterial, viral and mycotic infections in the lungs of immunocompromised patients are discussed.

[Infections in organ transplantations]

Infections play a crucial role in organ transplantations as possible complications. Viruses, bacteria, fungi and parasites are potential agents. The relevance of individual diseases depends on the organ transplanted. Morphology of the inflammatory reaction is given by the agent involved, but often several reactions can be caused by the same agent and different agents can also lead to the same reaction. Histology therefore provides concrete identification of the causal agent only in some cases, such that additional microbiological diagnostics are necessary. Results from these investigations should be transferred to the pathologist to distinguish between infection-associated changes and transplant rejection.

Molecular Basis of Pulmonary Disease

Pulmonary pathology includes a large spectrum of both neoplastic and non-neoplastic diseases that affect the lung. Many of these are a result of the unusual relationship of the lung with the outside world. Every breath that a human takes brings the outside world into the body in the form of infectious agents, organic and inorganic particles, and noxious agents of all types. Although the lung has many defense mechanisms to protect itself from these insults, these are not infallible; therefore, lung pathology arises. Damage to the lung is particularly important given the role of the lung in the survival of the organism. Any impairment of lung function has widespread effects throughout the body, since all organs depend on the lungs for the oxygen they need. Pulmonary pathology catalogs the changes in the lung tissues and the mechanisms through which these occur. This chapter presents a review of lung pathology and the current state of knowledge about the pathogenesis of each disease. It suggests that a clear understanding of both morphology and mechanism is required for the development of new therapies and preventive measures.