Fulminant legionellosis in two patients treated with infliximab for Crohn's disease: case series and literature review

Viewing Legionella pneumophila Pathogenesis through an Immunological Lens

Legionella pneumophila is the causative agent of the severe pneumonia Legionnaires' disease. L. pneumophila is ubiquitously found in freshwater environments, where it replicates within free-living protozoa. Aerosolization of contaminated water supplies allows the bacteria to be inhaled into the human lung, where L. pneumophila can be phagocytosed by alveolar macrophages and replicate intracellularly. The Dot/Icm type IV secretion system (T4SS) is one of the key virulence factors required for intracellular bacterial replication and subsequent disease. The Dot/Icm apparatus translocates more than 300 effector proteins into the host cell cytosol. These effectors interfere with a variety of cellular processes, thus enabling the bacterium to evade phagosome-lysosome fusion and establish an endoplasmic reticulum-derived Legionella-containing vacuole, which facilitates bacterial replication. In turn, the immune system has evolved numerous strategies to recognize intracellular bacteria such as L. pneumophila, leading to potent inflammatory responses that aid in eliminating infection. This review aims to provide an overview of L. pneumophila pathogenesis in the context of the host immune response.

Extreme Rhabdomyolysis, Acute Renal Failure, and Protracted Ileus in a Case of Legionella Pneumonia

A 53-year-old man developed a Legionella pneumophila pneumonia complicated by rhabdomyolysis, acute kidney injury, and protracted ileus. Risk factors were smoking and chronic alcoholism, but the patient had no history of previous abdominal surgery. Hemodialysis was required for a period of 5 weeks with a full renal recovery. Pneumonia required respiratory support but for a limited period of 6 days. The protracted course of the ileus led to explorative laparotomy despite negative computed tomography findings. No cause of mechanical obstruction was found at surgery and common etiologies of intestinal obstruction were excluded. Parenteral nutrition was needed for a total of 4 weeks, before recovery of intestinal motility. This case illustrates the apparent discrepancy between the pulmonary symptoms and the extrapulmonary manifestations that could be seen as a consequence of an exaggerated immune response.

When Diarrhea Can Become Deadly: Legionnaires' Disease Complicated by Bowel Obstruction

Legionnaires’ disease may present with a broad spectrum of illnesses and nonspecific extrapulmonary symptoms including diarrhea. To our knowledge, bowel obstruction has not been reported as a manifestation of Legionella. We present a unique case of Legionnaires’ disease contributing to a small bowel obstruction.

Legionnaire's Disease and Immunosuppressive Drugs

Immunosuppressive agents predispose patients to legionnaire's disease. Patients receiving tumor necrosis factor antagonists are generally not severely immunocompromised by the underlying disease. In patients with malignancy receiving immunosuppressive therapies, it is difficult to balance the underlying disease versus the therapy used. Transplant recipients are often on multiple drugs, including immunosuppressants. It seems that immunosuppressive drugs add to the risk for legionella infection. The index of suspicion should be high for legionella infection early during a compatible clinical syndrome. The control of Legionella species and prevention of transmission should be the foremost goal in protecting susceptible populations from Legionnaire's disease.

TNF and TNF-receptors: From mediators of cell death and inflammation to therapeutic giants - past, present and future

Tumor Necrosis Factor (TNF), initially known for its tumor cytotoxicity, is a potent mediator of inflammation, as well as many normal physiological functions in homeostasis and health, and anti-microbial immunity. It also appears to have a central role in neurobiology, although this area of TNF biology is only recently emerging. Here, we review the basic biology of TNF and its normal effector functions, and discuss the advantages and disadvantages of therapeutic neutralization of TNF - now a commonplace practice in the treatment of a wide range of human inflammatory diseases. With over ten years of experience, and an emerging range of anti-TNF biologics now available, we also review their modes of action, which appear to be far more complex than had originally been anticipated. Finally, we highlight the current challenges for therapeutic intervention of TNF: (i) to discover and produce orally delivered small molecule TNF-inhibitors, (ii) to specifically target selected TNF producing cells or individual (diseased) tissue targets, and (iii) to pre-identify anti-TNF treatment responders. Although the future looks bright, the therapeutic modulation of TNF now moves into the era of personalized medicine with society's challenging expectations of durable treatment success and of achieving long-term disease remission.

Legionnaires’ Disease and Use of Tumor Necrosis Factor-Αlpha Inhibitors: A Forthcoming Problem?

Aim: To establish a review in the current literature and to analyze the relation Legionnaires’ disease – TNF-α inhibitors, in order to estimate the real indications for such connection.Material and Methods: The electronic data for PubMed and Google Scholar have been searched, according to the vocabulary: legionellosis, epidemiology, outbreak, diagnosis, pathogenesis, therapy, TNF-α inhibitors, indications, side effects, risk of infection. The obtained studies have been selected in English, according to the relevance by the topic.Results: Selected papers, consisted of ten studies and eight case reports, yielded 35 cases of Legionnaires' disease associated with the use of TNF- α inhibitor treatment.Discussion: There is a prevailing conclusion for increased risk of serious infections while using TNF-α inhibitors and also a deficiency of studies for an association of Legionnaires’ disease with the use of TNF-α inhibitors. Sub-diagnosing and no-existence of screening before the anti-TNF-α therapy blur the factual profile for the researched relation. The possibility for latent infection has not been sufficiently researched.Conclusion: There are indications that Legionnaires’ disease in the therapy with TNF-α inhibitors is indeed a forthcoming problem. Additional target researches are required in order to establish the position of Legionnaires’ disease in the mosaic of anti - TNF-α therapy.

Legionella pneumophila serotype 1 pneumonia in patient receiving adalimumab

We describe a case of severe pneumonia caused by Legionella pneumophila serotype 1 in a woman receiving the tumor necrosis factor–α antagonist to treat rheumatoid arthritis. As use of tumor necrosis factor–α inhibitors increase, clinicians should consider their possible association with legionellosis.

Legionella pneumophila type II secretion dampens the cytokine response of infected macrophages and epithelia

The type II secretion (T2S) system of Legionella pneumophila is required for the ability of the bacterium to grow within the lungs of A/J mice. By utilizing mutants lacking T2S (lsp), we now document that T2S promotes the intracellular infection of both multiple types of macrophages and lung epithelia. Following infection of macrophages, lsp mutants (but not a complemented mutant) elicited significantly higher levels of interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), IL-10, IL-8, IL-1β, and MCP-1 within tissue culture supernatants. A similar result was obtained with infected lung epithelial cell lines and the lungs of infected A/J mice. Infection with a mutant specifically lacking the T2S-dependent ProA protease (but not a complemented proA mutant) resulted in partial elevation of cytokine levels. These data demonstrate that the T2S system of L. pneumophila dampens the cytokine/chemokine output of infected host cells. Upon quantitative reverse transcription (RT)-PCR analysis of infected host cells, an lspF mutant, but not the proA mutant, produced significantly higher levels of cytokine transcripts, implying that some T2S-dependent effectors dampen signal transduction and transcription but that others, such as ProA, act at a posttranscriptional step in cytokine expression. In summary, the impact of T2S on lung infection is a combination of at least three factors: the promotion of growth in macrophages, the facilitation of growth in epithelia, and the dampening of the chemokine and cytokine output from infected host cells. To our knowledge, these data are the first to identify a link between a T2S system and the modulation of immune factors following intracellular infection.

Crohn's disease as an immunodeficiency

The pathogenesis of Crohn's disease (CD) has widely been regarded as the consequence of a dysregulated T-cell-mediated response to intestinal microbes, and the majority of the worldwide research effort has focused on characterizing and treating the chronic inflammatory phase of the disease. However, recent molecular biological and clinical investigations indicate that CD is actually a primary immunodeficiency. At first counter-intuitive, the apparent paradox of a pathogenic innate immune defect can be linked mechanistically to the granulomatous chronic inflammation characteristic of the disease. Genome-wide association studies have corroborated the involvement of innate immune dysfunction in the pathogenesis of CD, but less than 20% of the heritable risk is accounted for. By contrast, in vitro and in vivo stimulation of the immune system has highlighted novel areas of interest that may lead to the development of targeted therapeutic and diagnostic tools.