BPI-ANCA in transporter associated with antigen presentation (TAP) deficiency: possible role in susceptibility to Gram-negative bacterial infections

Vaskulitis mimics

Idiopathische Vaskulitiden sind seltene entzündliche Systemerkrankungen, die nach der Chapel-Hill Konsensus-Nomenklatur nach der Größe der prädominant betroffenen Gebiete von Blutgefäßen (große, mittelgroße, kleine Gefäße und Gefäße variabler Größe) eingeteilt werden. Vaskulitis mimics sind Syndrome, die ein ähnliches klinisches Bild hervorrufen oder leicht mit einer idiopathischen Vaskulitis verwechselt werden und teils sogar ein Krankheitsbild, das klinisch und histologisch einer Vaskulitis gleicht, auslösen können. Die Zahl der Vaskulitis mimics ist groß, je nach betroffenem Gefäßgebiet kommen hereditäre Erkrankungen des Bindegewebes, genetisch bedingte Immundefekt- und Autoinflammationssyndrome, infektiöse Erkrankungen, seltene entzündliche Systemerkrankungen, Tumorerkrankungen, medikamenteninduzierte Syndrome und zahlreiche weitere infrage. In diesem Review wird eine Auswahl klassischer Imitatoren von Vaskulitiden, orientiert an der Größe der betroffenen Blutgefäße präsentiert und Konstellationen, die typische „Fallstricke“ in der klinischen Abklärung darstellen können, diskutiert.

Differential Enhancement of Neutrophil Phagocytosis by Anti-Bactericidal/Permeability-Increasing Protein Antibodies

Bactericidal/permeability-increasing protein (BPI) plays a major role in innate immunity through the ability of the N-terminal domain (NTD) to bind LPS, mediate cytotoxicity, and block LPS-induced inflammation. The C-terminal domain mediates phagocytosis of bacteria bound to the NTD. These two domains are linked by a surface-exposed loop at amino acids 231-249 for human BPI, known as the "hinge region." Autoantibodies to human BPI are prevalent in many chronic lung diseases; their presence is strongly correlated with Pseudomonas aeruginosa and with worse lung function in patients with cystic fibrosis and bronchiectasis. Although prior literature has reported BPI neutralization effect with autoantibodies targeting either NTD or C-terminal domain, the functionality of BPI Ab to the hinge region has never been investigated. Here, we report that Ab responses to the BPI hinge region mediate a remarkably selective potentiation of BPI-dependent phagocytosis of P. aeruginosa with both human and murine neutrophils in vitro and in vivo. These findings indicate that autoantibodies to the BPI hinge region might enhance bacterial clearance.

Stem cell transplantation as treatment for major histocompatibility class I deficiency

Major histocompatibility class I deficiency, due to genetic lesions in TAP1, TAP2, TAPBP, or B2M, manifests with recurrent sinopulmonary infections and granulomatous skin ulceration, and is predominately treated with antimicrobial prophylaxis and chest physiotherapy. One previous report of hematopoietic stem cell transplantation has been described in the literature, demonstrating cure of the immune defect without significant graft-versus-host disease. In this report, we expand the literature on HSCT in MHC-I deficiency with follow-up of the original patient, demonstrating maintained resolution of normal immune function and regression of the granulomatous rash 15 years post-transplant, and describe a further patient with mycobacterial disease whose transplant course was complicated by severe graft-versus-host disease.

[Vasculitis mimics]

Vasculitis mimics need to be differentiated from primary and secondary vasculitides as described in the Chapel Hill nomenclature. The clinical symptomatology resembles that of vasculitis of small and medium, rarely also large vessels and hence imitates the classical vasculitic disorders. Pathogenetically, the causes are partly genetic mutations, embolization syndromes, infections and substance abuse. Also, B‑cell lymphomas can mimic vasculitis. The present manuscript summarizes the vasculitis mimics.

Genetic variations of TAP1 gene exon 3 affects gene expression and Escherichia coli F18 resistance in piglets

Firstly, our research group identified Sutai pigs’ phenotypes that exhibited extreme resistance and susceptibility to the Escherichia coli F18 respectively, and then eight ETEC (Enterotoxigenic Escherichia coli) F18-resistant piglets and eight ETEC F18-sensitive piglets were selected. Then, the TAP1 (Transporter associated with antigen processing) mRNA relative expression levels were analyzed in 11 tissues of the resistant and susceptible phenotypes. Simultaneously, we detected the genetic variations in exon 3 of the TAP1 gene and evaluated the TAP1 mRNA expression levels among the different genotype pigs to study the effects of the genetic variation on gene expression, and the E. coli F18 resistance. The results revealed higher expression levels in the resistant genotypes than that in the susceptible genotypes in 11 tissues, with significant differences in the spleen, lymph node, lung, thymus, duodenum and jejunum. Furthermore, a G729A mutation was identified in the TAP1 gene exon 3, and this mutation deviates from Hardy-Weinberg equilibrium (p < 0.01). The TAP1 mRNA levels in GG genotype were significantly higher than that in the other two genotypes, with significant differences in the liver, lung, kidney, thymus, lymph node, duodenum and jejunum tissues. We speculated that high expression of the TAP1 gene might confer resistance against the E. coli F18, the G729A mutation had a significant effect on the mRNA expression, and individuals with the GG genotype possessed a stronger ability to resist the E. coli F18 infection.

[Secondary vasculitides and vasculitis mimics]

Secondary vasculitis is a form of vasculitis for which an underlying disease is known. Diseases associated with secondary vasculitis include infections, drug hypersensitivity, malignancy, rheumatoid arthritis, collagen vascular disease and sarcoidosis. Moreover, there are numerous conditions that can mimic vasculitis clinically, in laboratory testing, radiographically and in histopathology. It is evident that distinguishing primary vasculitis from secondary vasculitis and also vascular inflammation from non-vasculitic disorders (vasculitis mimics) has significant therapeutic implications.

Bactericidal/permeability increasing protein: a multifaceted protein with functions beyond LPS neutralization

Bactericidal permeability increasing protein (BPI), a 55-60 kDa protein, first reported in 1975, has gone a long way as a protein with multifunctional roles. Its classical role in neutralizing endotoxin (LPS) raised high hopes among septic shock patients. Today, BPI is not just a LPS-neutralizing protein, but a protein with diverse functions. These functions can be as varied as inhibition of endothelial cell growth and inhibition of dendritic cell maturation, or as an anti-angiogenic, chemoattractant or opsonization agent. Though the literature available is extremely limited, it is fascinating to look into how BPI is gaining major importance as a signalling molecule. In this review, we briefly summarize the recent research focused on the multiple roles of BPI and its use as a therapeutic.

Deficient expression of bactericidal/permeability-increasing protein in immunocompromised hosts: translational potential of replacement therapy

BPI (bactericidal/permeability-increasing protein) is a 55 kDa anti-infective molecule expressed in neutrophil and eosinophil granules and on some epithelial cells. BPI's high affinity for the lipid A region of endotoxin targets its opsonizing, microbicidal and endotoxin-neutralizing activities towards Gram-negative bacteria. Several immunocompromised patient populations demonstrate BPI deficiency, including newborns, those with anti-neutrophil cytoplasmic antibodies (as in cystic fibrosis and HIV infection) and those exposed to radiochemotherapy. BPI may be replenished by administering agents that induce its expression or by administration of recombinant BPI congeners, potentially shielding BPI-deficient individuals against Gram-negative bacterial infection, endotoxemia and its toxic sequelae.

Clinical and immunological features of drug-induced and infection-induced proteinase 3-antineutrophil cytoplasmic antibodies and myeloperoxidase-antineutrophil cytoplasmic antibodies and vasculitis

PURPOSE OF REVIEW

Drugs and infections may induce antineutrophil cytoplasmic antibodies (ANCA) and vasculitic manifestations mimicking ANCA-associated vasculitides (AAV) and mechanisms relevant in their pathogenesis. This review summarizes the most recent findings in this field.

RECENT FINDINGS

Drug-induced and infection-induced proteinase 3 (PR3)-ANCA and myeloperoxidase (MPO)-ANCA may be associated with a vasculitis clinically resembling AAV. Mechanisms relevant for the break of tolerance and induction of ANCA (e.g. danger signals, superantigens, neutrophil extracellular traps, protease-activated receptor-2, IL-17 cells) may be shared to some extent between drug-induced and infection-induced ANCA-positive vasculitis and AAV, especially with regard to the potential role of infection in Wegener's granulomatosis. Differences in immunopathology, clinical presentation, and functional aspects of ANCA help to distinguish drug-induced and infection-induced ANCA-positive vasculitis from AAV, and present new avenues for future research in this field.

SUMMARY

Medications and infections, which induce PR3-ANCA and MPO-ANCA, have to be considered in the differential diagnosis of primary AAV. Moreover, there is clinical and experimental evidence for an association between certain drugs and infections with ANCA-production. Analysis of ANCA-induction in such conditions also sheds new light on our understanding of immune mechanisms relevant in the break of tolerance and ANCA-production in AAV.

A Novel Role for the Bactericidal/Permeability Increasing Protein in Interactions of Gram-Negative Bacterial Outer Membrane Blebs with Dendritic Cells

The bactericidal/permeability-increasing protein (BPI) is thought to play an important role in killing and clearance of Gram-negative bacteria and the neutralization of endotoxin. A possible role for BPI in clearance of cell-free endotoxin has also been suggested based on studies with purified endotoxin aggregates and blood monocytes. Because the interaction of BPI with cell-free endotoxin, during infection, occurs mainly in tissue and most likely in the form of shed bacterial outer membrane vesicles ("blebs"), we examined the effect of BPI on interactions of metabolically labeled ([(14)C]-acetate) blebs purified from Neisseria meningitidis serogroup B with either human monocyte-derived macrophages or monocyte-derived dendritic cells (MDDC). BPI produced a dose-dependent increase (up to 3-fold) in delivery of (14)C-labeled blebs to MDDC, but not to monocyte-derived macrophages in the presence or absence of serum. Both, fluorescently labeled blebs and BPI were internalized by MDDC under these conditions. The closely related LPS-binding protein, in contrast to BPI, did not increase association of the blebs with MDDC. BPI-enhanced delivery of the blebs to MDDC did not increase cell activation but permitted CD14-dependent signaling by the blebs as measured by changes in MDDC morphology, surface expression of CD80, CD83, CD86, and MHC class II and secretion of IL-8, RANTES, and IP-10. These findings suggest a novel role of BPI in the interaction of bacterial outer membrane vesicles with dendritic cells that may help link innate immune recognition of endotoxin to Ag delivery and presentation.

The bactericidal/permeability-increasing protein (BPI) in infection and inflammatory disease

Gram-negative bacteria (GNB) and their endotoxin present a constant environmental challenge. Endotoxins can potently signal mobilization of host defenses against invading GNB but also potentially induce severe pathophysiology, necessitating controlled initiation and resolution of endotoxin-induced inflammation to maintain host integrity. The bactericidal/permeability-increasing protein (BPI) is a pluripotent protein expressed, in humans, mainly neutrophils. BPI exhibits strong antimicrobial activity against GNB and potent endotoxin-neutralizing activity. BPI mobilized with neutrophils in response to invading GNB can promote intracellular and extracellular bacterial killing, endotoxin neutralization and clearance, and delivery of GNB outer membrane antigens to dendritic cells. Tissue expression by dermal fibroblasts and epithelia could further amplify local levels of BPI and local interaction with GNB and endotoxin, helping to constrain local tissue infection and inflammation and prevent systemic infection and systemic inflammation. This review article focuses on the structural and functional properties of BPI with respect to its contribution to host defense during GNB infections and endotoxin-induced inflammation and the genesis of autoantibodies against BPI that can blunt BPI activity and potentially contribute to chronic inflammatory disease.

Description of HLA class I- and CD8-deficient patients: Insights into the function of cytotoxic T lymphocytes and NK cells in host defense

Over the last few years, several patients with defects in the HLA class I presentation pathway have been described. Analysis of their clinical symptoms and immunological parameters have led to the identification of several unexpected findings which are of importance to understand the role of HLA class I-dependent immune responses in host defense. Here, we will describe and compare clinical manifestations and immunological findings of patients with defects in the peptide transporter proteins (TAP complex), tapasin and CD8 molecules.

From infection to autoimmunity: a new model for induction of ANCA against the bactericidal/permeability increasing protein (BPI)

Antineutrophil cytoplasmic autoantibodies against the neutrophil granule bactericidal/permeability increasing protein (BPI-ANCA) have been found in diseases of different etiologies, such as cystic fibrosis, TAP deficiency or inflammatory bowel diseases. A common feature of these conditions is the chronic or profuse exposure of the host to Gram-negative bacteria and their endotoxin. BPI plays an important role in killing Gram-negative bacteria as well as neutralization and disposal of their endotoxin. During this interaction BPI can direct the delivery of complexes which contain endotoxin and bacterial outer membrane proteins to antigen presenting cells. Based on recent findings on how complexes of endotoxin and protein antigens need to be processed by dendritic cells in order to become presented on MHC class II molecules, a model can be proposed how Gram-negative bacterial infections can be linked to the generation of autoantibodies against BPI.

Clinical and immunological aspects of HLA class I deficiency

Human leukocyte antigen (HLA) class I deficiency is a rare disease with remarkable clinical and biological heterogeneity. The spectrum of possible manifestations extends from the complete absence of symptoms to life-threatening disease conditions. It is usually diagnosed when HLA class I serological typing is unsuccessful; flow cytometric studies then reveal a severe reduction in the cell surface expression of HLA class I molecules (90-99% reduction compared to normal cells). In most cases to date, this low expression is due to a homozygous inactivating mutation in one of the two subunits of the transporter associated with antigen processing (TAP), critically involved in the peptide loading of HLA class I molecules. Although asymptomatic cases have been described, TAP deficiencies are usually characterized by chronic bacterial infections of the upper and lower airways, evolving to bronchiectasis, and in half of the cases, also skin ulcers with features of a chronic granulomatous inflammation. Despite the defect in HLA class-I-mediated presentation of viral antigens to cytotoxic T cells, the patients do not suffer from severe viral infections, presumably because of other efficient antiviral defence mechanisms such as antibodies, non-HLA-class-I-restricted cytotoxic effector cells and CD8+ T-cell responses to TAP-independent antigens. Treatment is at present exclusively symptomatic, and should particularly focus on the prevention of bronchiectasis, which requires early detection.

Chaperoning antigen presentation by MHC class II molecules and their role in oncogenesis

Tumor vaccine development aimed at stimulating the cellular immune response focuses mainly on MHC class I molecules. This is not surprising since most tumors do not express MHC class II or CD1 molecules. Nevertheless, the most successful targets for cancer immunotherapy, leukemia and melanoma, often do express MHC class II molecules, which leaves no obvious reason to ignore MHC class II molecules as a mediator in anticancer immune therapy. We review the current state of knowledge on the process of MHC class II-restricted antigen presentation and subsequently discuss the consequences of MHC class II expression on tumor surveillance and the induction of an efficient MHC class II mediated antitumor response in vivo and after vaccination.

[Adult-onset primary immunodeficiencies]

Different individuals with the same kind of primary immunodeficiency may start having symptoms from early childhood on, or alternatively much later in adult life, or never. The differences in phenotype can only partly be deduced from genotype-analysis or--in case of female patients with X-linked diseases--from age-related skewing of lyonisation. The role of compensatory immune mechanisms is less clear. The microbial spectrum of infections is usually the same for both adult and infantile forms of a special primary immunodeficiency syndrome. Yet, many of the adult forms are associated with non-infectious complications, such as granuloma formation, autoimmunity or tumors. Besides standard antibiotic treatment and IgG replacement therapy, there are now different cytokine- or enzyme-replacement regimens available for some of the primary immunodeficiencies. However, exact diagnostic classification of the immunodeficiency should be obtained before such treatment modalities are used. Adult primary immunodeficiency syndromes therefore represent a challenge to both clinicians and molecular biologists.