Hrishikesh S. Kulkarni

A C3(H20) recycling pathway is a component of the intracellular complement system

An intracellular complement system (ICS) has recently been described in immune and nonimmune human cells. This system can be activated in a convertase-independent manner from intracellular stores of the complement component C3. The source of these stores has not been rigorously investigated. In the present study, Western blotting identified a band corresponding to C3 in freshly isolated human peripheral blood cells that was absent in corresponding cell lines. One difference between native cells and cell lines was the time absent from a fluid-phase complement source; therefore, we hypothesized that loading C3 from plasma was a route of establishing intracellular C3 stores. We found that many types of human cells specifically internalized C3(H2O), the hydrolytic product of C3, and not native C3, from the extracellular milieu. Uptake was rapid, saturable, and sensitive to competition with unlabeled C3(H2O), indicating a specific mechanism of loading. Under steady-state conditions, approximately 80% of incorporated C3(H2O) was returned to the extracellular space. These studies identify an ICS recycling pathway for C3(H2O). The loaded C3(H2O) represents a source of C3a, and its uptake altered the cytokine profile of activated CD4+ T cells. Importantly, these results indicate that the impact of soluble plasma factors should be considered when performing in vitro studies assessing cellular immune function.

Complement’s hidden arsenal: New insights and novel functions inside the cell

Highlights New studies have demonstrated major new intracellular roles for complement:C3 is a damage‐associated molecular pattern that can enhance intracellular innate immunity and help control cell survival.A C3(H2O) recycling pathway is a component of the intracellular complement system.Autocrine activation of CD46 via T‐cell derived C3b plays a key role in nutrient uptake and cellular metabolism.C3 activation fragments and factor H act as chaperones for the processing of apoptotic cargo.Intracellular C5 activation is essential for NLRP3 inflammasome assembly in CD4+ T cells. The full importance and mechanisms of complement’s hidden intracellular arsenal continue to be elucidated. Other intracellular players including the C3a receptor (C3aR), the C5a receptor (C5aR), and factor B (FB) also are currently being evaluated. These new roles also suggest new therapeutic approaches. Abstract A key component of both innate and adaptive immunity, new understandings of the complement system are expanding its roles beyond that traditionally appreciated. Evidence is accumulating that complement has an intracellular arsenal of components that provide not only immune defense, but also assist in key interactions for host cell functions. Although early work has primarily centered on T cells, the intracellular complement system likely functions in many if not most cells of the body. Some of these functions may trace their origins to the primitive complement system that began as a primeval form of C3 likely tasked for protection from intracellular pathogen invasion. This later expanded to include extracellular defense as C3 became a secreted protein to patrol the vasculature. Other components were added to the growing system including regulators to protect host cells from the indiscriminate effects of this potent system. Contemporary cells may retain some of these vestigial remnants. We now know that a) C3 serves as a damage‐associated molecular pattern (in particular by coating pathogens that translocate into cells), b) most cells store C3 and recycle C3(H2O) for immediate use, and c) C3 assists in cellular survival and metabolic reprogramming. Other components also are part of this hidden arsenal including C5, properdin, factors H and B, and complement receptors. Importantly, better definition of the intracellular complement system may translate into new target discovery to assist in creating the next generation of complement therapeutics.

Antibody-Mediated Rejection in Lung Transplantation

There has been increasing awareness of antibody-mediated rejection (AMR) as an important cause of graft failure after lung transplantation in recent years. However, the diagnostic criteria for pulmonary AMR are not well defined. All four tenets of AMR in kidney and heart transplantation, graft dysfunction, complement component deposition, circulating donor-specific antibodies (DSA), and histopathologic changes consistent with AMR are infrequently present in lung transplantation. Nonetheless, the lung transplant community has made important progress recognizing cases of AMR and developing a definition. However, AMR is often refractory to therapy resulting in graft failure and death. In this review, we discuss the progress and challenges in the diagnosis and therapeutic options for pulmonary AMR. In addition, we briefly examine emerging paradigms of C4d-negative AMR and chronic AMR and conclude that significant progress is needed to mitigate the effects of humoral immune responses after lung transplantation.

The Human Complement System: Basic Concepts and Clinical Relevance

Abstract The complement system is a key player in innate immunity and a major effector arm of humoral immunity. Its activating components are a group of plasma proteins, whose triggering consists of a series of sequential protease-based steps similar to the coagulation, fibrinolytic, and contact pathways. Complement activation is linked to cellular responses by the recognition of cleaved complement protein fragments by receptors on leukocytes and vascular cells. The three primary roles of complement in host defense against infection are to (1) activate an inflammatory response; (2) opsonize microbial pathogens for immune adherence; and (3) damage membranes, including lysis of susceptible organisms. The complement cascade is amplified at several steps so that it has the potential to induce a rapid and massive opsonic and inflammatory response. Complement activation is normally highly targeted and strictly regulated to focus this response. However, complement activation also contributes to tissue injury in infectious, autoimmune, and acute and chronic inflammatory diseases. This chapter gives an overview of the “workings” of the complement system, a brief review of complement deficiency, and discussion of the role of complement in diseases of inflammation, autoimmunity, and debris disposal.

Bronchiolitis-obliterans syndrome-free survival following lung transplantation - an International Society for Heart and Lung Transplantation (ISHLT) Thoracic Transplant Registry analysis

BACKGROUNDnLung transplant (LTx) recipients have low long-term survival and a high incidence of bronchiolitis obliterans syndrome (BOS). However, few long-term, multicenter, and precise estimates of BOS-free survival (a composite outcome of death or BOS) incidence exist.nnnMETHODSnThis retrospective cohort study of primary LTx recipients (1994-2011) reported to the International Society of Heart and Lung Transplantation Thoracic Transplant Registry assessed outcomes through 2012. For the composite primary outcome of BOS-free survival, we used Kaplan-Meier survival and Cox proportional hazards regression, censoring for loss to follow-up, end of study, and re-LTx. Although standard Thoracic Transplant Registry analyses censor at the last consecutive annual complete BOS status report, our analyses allowed for partially missing BOS data.nnnRESULTSnDue to BOS reporting standards, 99.1% of the cohort received LTx in North America. During 79,896 person-years of follow-up, single LTx (6,599 of 15,268 [43%]) and bilateral LTx (8,699 of 15,268 [57%]) recipients had a median BOS-free survival of 3.16 years (95% confidence interval [CI], 2.99-3.30 years) and 3.58 years (95% CI, 3.53-3.72 years), respectively. Almost 90% of the single and bilateral LTx recipients developed the composite outcome within 10 years of transplantation. Standard Registry analyses overestimated median BOS-free survival by 0.42 years and underestimated the median survival after BOS by about a half-year for both single and bilateral LTx (p < 0.05).nnnCONCLUSIONSnMost LTx recipients die or develop BOS within 4 years, and very few remain alive and free from BOS at 10 years post-LTx. Less inclusive Thoracic Transplant Registry analytic methods tend to overestimate BOS-free survival. The Registry would benefit from improved international reporting of BOS and other chronic lung allograft dysfunction (CLAD) events.

Voriconazole in lung transplant recipients – how worried should we be?

Invasive aspergillosis (IA) is the most common invasive mold infection in solid organ transplant (SOT) recipients, occurring in 1-15% of recipients, with a 12-week mortality rate of 20-60%.1 Lung transplant (LTx) recipients are at the highest risk for IA among all SOT recipients, ranging from ulcerative tracheobronchitis, anastomotic site involvement and airway wall necrosis, to pneumonia, mediastinitis, empyema and disseminated fungemia. Additionally, Aspergillus colonization is an independent risk factor for chronic lung allograft dysfunction. Resultingly, a majority of LTx programs now use antifungal prophylaxis against Aspergillus. n nThis article is protected by copyright. All rights reserved.

Taking the detour

Hrishikesh S. Kulkarni, MD*1, William D. Chey, MD, Somnath Mookherjee, MD, Sanjay Saint, MD, MPH, Gregory M. Bump, MD Division of Pulmonary and Critical Care Medicine, Washington University in St. Louis, St. Louis, Missouri; Department of Medicine, University of Michigan Health System, Ann Arbor, Michigan; Department of Medicine, University of Washington, Seattle, Washington; Department of Internal Medicine, University of Michigan Health System, Ann Arbor, Michigan; Department of Veterans Affairs, Ann Arbor Healthcare System and Health Services Research and Development Center of Excellence, Ann Arbor, Michigan; Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.

A 43-Year-Old Man With Antisynthetase Syndrome Presenting With Acute Worsening of Dyspnea

A 43-year-old man with antisynthetase syndrome was seen in our pulmonary clinic for worsening dyspnea. He was recently diagnosed with antisynthetase syndrome because he had nonspecific interstitial pneumonitis on a surgical lung biopsy and polymyositis associated with anti-Jo-1 and anti-SSA-52 autoantibodies. Along with his worsening dyspnea, he also had a dry cough, lower extremity edema, and abdominal distension. He had gained 11 kg over 1 month. He had been taking prednisone 40 mg daily 2 months prior, which had been recently weaned to 20 mg daily. He had also been on mycophenolate mofetil but had recently discontinued it on his own.