Some Drugs Have Two Faces: Paradoxical Colitis in a Patient with Psoriatic Arthritis Previously Treated with Etanercept and IL-17 Inhibitors.

Tumor necrosis factor-alpha (TNF-α) and interleukin-17 (IL-17) inhibitors are among the most potent treatments for inflammatory arthropathies including rheumatoid arthritis, psoriasis, and spondyloarthropathies. The availability of these biologic agents have revolutionized the management of these conditions and improved patient outcomes. Though generally safe, these biologics may contribute to the induction or exacerbation of colitis. This paradoxical colitis has been observed in patients on TNF-α inhibitor etanercept and IL-17 inhibitors (secukinumab and ixekizumab). We report a case of a 46-year-old female with psoriasis and psoriatic arthritis who presented with gastrointestinal symptoms after treatment with etanercept and IL-17 inhibitors. She was later diagnosed with paradoxical indeterminate colitis that was masked and treated by subsequent biologics given for her RA and psoriatic arthritis. In this report, we will discuss the importance of considering paradoxical colitis in the differential diagnosis for patients even several years after TNF-α/IL-17 inhibitor initiation and explain why careful consideration must be made when initiating these colitis-inducing agents to treat patients with inflammatory disorders.

Mapping the T cell repertoire to a complex gut bacterial community.

Certain bacterial strains from the microbiome induce a potent, antigen-specific T cell response1-5. However, the specificity of microbiome-induced T cells has not been explored at the strain level across the gut community. Here, we colonize germ-free mice with complex defined communities (roughly 100 bacterial strains) and profile T cell responses to each strain. The pattern of responses suggests that many T cells in the gut repertoire recognize several bacterial strains from the community. We constructed T cell hybridomas from 92 T cell receptor (TCR) clonotypes; by screening every strain in the community against each hybridoma, we find that nearly all the bacteria-specific TCRs show a one-to-many TCR-to-strain relationship, including 13 abundant TCR clonotypes that each recognize 18 Firmicutes. By screening three pooled bacterial genomic libraries, we discover that these 13 clonotypes share a single target: a conserved substrate-binding protein from an ATP-binding cassette transport system. Peripheral regulatory T cells and T helper 17 cells specific for an epitope from this protein are abundant in community-colonized and specific pathogen-free mice. Our work reveals that T cell recognition of commensals is focused on widely conserved, highly expressed cell-surface antigens, opening the door to new therapeutic strategies in which colonist-specific immune responses are rationally altered or redirected.

Strain dropouts reveal interactions that govern the metabolic output of the gut microbiome.

The gut microbiome is complex, raising questions about the role of individual strains in the community. Here, we address this question by constructing variants of a complex defined community in which we eliminate strains that occupy the bile acid 7α-dehydroxylation niche. Omitting Clostridium scindens (Cs) and Clostridium hylemonae (Ch) eliminates secondary bile acid production and reshapes the community in a highly specific manner: eight strains change in relative abundance by >100-fold. In single-strain dropout communities, Cs and Ch reach the same relative abundance and dehydroxylate bile acids to a similar extent. However, Clostridium sporogenes increases >1,000-fold in the ΔCs but not ΔCh dropout, reshaping the pool of microbiome-derived phenylalanine metabolites. Thus, strains that are functionally redundant within a niche can have widely varying impacts outside the niche, and a strain swap can ripple through the community in an unpredictable manner, resulting in a large impact on an unrelated community-level phenotype.

Design, construction, and in vivo augmentation of a complex gut microbiome.

Efforts to model the human gut microbiome in mice have led to important insights into the mechanisms of host-microbe interactions. However, the model communities studied to date have been defined or complex, but not both, limiting their utility. Here, we construct and characterize in vitro a defined community of 104 bacterial species composed of the most common taxa from the human gut microbiota (hCom1). We then used an iterative experimental process to fill open niches: germ-free mice were colonized with hCom1 and then challenged with a human fecal sample. We identified new species that engrafted following fecal challenge and added them to hCom1, yielding hCom2. In gnotobiotic mice, hCom2 exhibited increased stability to fecal challenge and robust colonization resistance against pathogenic Escherichia coli. Mice colonized by either hCom2 or a human fecal community are phenotypically similar, suggesting that this consortium will enable a mechanistic interrogation of species and genes on microbiome-associated phenotypes.

Impact of mode of delivery on outcomes in patients with perianal Crohn's disease.

BACKGROUND: Crohn's disease (CD) often affects women during the reproductive years. Although several studies have examined the impact of pregnancy on luminal disease, limited literature exists in those with perianal CD. Decision regarding mode of delivery is a unique challenge in such patients due to concerns regarding the effect of pelvic floor trauma during delivery on preexisting perianal involvement. METHODS: We performed a retrospective chart review of patients with CD with established perianal disease undergoing either vaginal delivery or caesarean section (C-section) at our institutions. We examined the occurrence of symptomatic perianal disease flares within 5 years after delivery in such women compared with nonpregnant CD controls. We also compared the occurrence of such flares between the 2 modes of delivery in women with established perianal CD. RESULTS: We identified 61 pregnant patients with CD with established perianal disease (11 vaginal delivery, 50 through C-section) and 61 nonpregnant CD controls with perianal disease. One-third of the C-sections were primarily for obstetric indications. Six of the vaginal deliveries were complicated. Approximately, 36% of cases had a symptomatic perianal flare within 1 year after delivery. This was similar across both modes of delivery (P = 0.53) and similar to nonpregnant patients with CD. There was no difference in the rates of perianal surgical intervention or luminal disease flares in our population based on mode of delivery or between pregnant patients with CD and nonpregnant CD controls. CONCLUSIONS: We observed no difference in risk of symptomatic perianal flares in patients with established perianal CD delivering vaginally or through C-section.

The giant protein Ebh is a determinant of Staphylococcus aureus cell size and complement resistance.

Staphylococcus aureus USA300, the clonal type associated with epidemic community-acquired methicillin-resistant S. aureus (MRSA) infections, displays the giant protein Ebh on its surface. Mutations that disrupt the ebh reading frame increase the volume of staphylococcal cells and alter the cross wall, a membrane-enclosed peptidoglycan synthesis and assembly compartment. S. aureus ebh variants display increased sensitivity to oxacillin (methicillin) as well as susceptibility to complement-mediated killing. Mutations in ebh are associated with reduced survival of mutant staphylococci in blood and diminished virulence in mice. We propose that Ebh, following its secretion into the cross wall, contributes to the characteristic cell growth and envelope assembly pathways of S. aureus, thereby enabling complement resistance and the pathogenesis of staphylococcal infections.

Coagulases as determinants of protective immune responses against Staphylococcus aureus.

During infection, Staphylococcus aureus secretes two coagulases (Coa and von Willebrand factor binding protein [vWbp]), which, following an association with host prothrombin and fibrinogen, form fibrin clots and enable the establishment of staphylococcal disease. Within the genomes of different S. aureus isolates, coagulase gene sequences are variable, and this has been exploited for a classification of types. We show here that antibodies directed against the variable prothrombin binding portion of coagulases confer type-specific immunity through the neutralization of S. aureus clotting activity and protection from staphylococcal disease in mice. By combining variable portions of coagulases from North American isolates into hybrid Coa and vWbp proteins, a subunit vaccine that provided protection against challenge with different coagulase-type S. aureus strains in mice was derived.

A play in four acts: Staphylococcus aureus abscess formation.

Staphylococcus aureus is an important human pathogen that causes skin and soft tissue abscesses. Abscess formation is not unique to staphylococcal infection and purulent discharge has been widely considered a physiological feature of healing and tissue repair. Here we present a different view, whereby S. aureus deploys specific virulence factors to promote abscess lesions that are distinctive for this pathogen. In support of this model, only live S. aureus is able to form abscesses, requiring genes that act at one or more of four discrete stages during the development of these infectious lesions. Protein A and coagulases are distinctive virulence attributes for S. aureus, and humoral immune responses specific for these polypeptides provide protection against abscess formation in animal models of staphylococcal disease.

Contribution of coagulases towards Staphylococcus aureus disease and protective immunity.

The bacterial pathogen Staphylococcus aureus seeds abscesses in host tissues to replicate at the center of these lesions, protected from host immune cells via a pseudocapsule. Using histochemical staining, we identified prothrombin and fibrin within abscesses and pseudocapsules. S. aureus secretes two clotting factors, coagulase (Coa) and von Willebrand factor binding protein (vWbp). We report here that Coa and vWbp together are required for the formation of abscesses. Coa and vWbp promote the non-proteolytic activation of prothrombin and cleavage of fibrinogen, reactions that are inhibited with specific antibody against each of these molecules. Coa and vWbp specific antibodies confer protection against abscess formation and S. aureus lethal bacteremia, suggesting that coagulases function as protective antigens for a staphylococcal vaccine.

Nontoxigenic protein A vaccine for methicillin-resistant Staphylococcus aureus infections in mice.

The current epidemic of hospital- and community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections has caused significant human morbidity, but a protective vaccine is not yet available. Prior infection with S. aureus is not associated with protective immunity. This phenomenon involves staphylococcal protein A (SpA), an S. aureus surface molecule that binds to Fcgamma of immunoglobulin (Ig) and to the Fab portion of V(H)3-type B cell receptors, thereby interfering with opsonophagocytic clearance of the pathogen and ablating adaptive immune responses. We show that mutation of each of the five Ig-binding domains of SpA with amino acid substitutions abolished the ability of the resulting variant SpA(KKAA) to bind Fcgamma or Fab V(H)3 and promote B cell apoptosis. Immunization of mice with SpA(KKAA) raised antibodies that blocked the virulence of staphylococci, promoted opsonophagocytic clearance, and protected mice against challenge with highly virulent MRSA strains. Furthermore, SpA(KKAA) immunization enabled MRSA-challenged mice to mount antibody responses to many different staphylococcal antigens.

IsdA and IsdB antibodies protect mice against Staphylococcus aureus abscess formation and lethal challenge.

Staphylococcus aureus is the most frequent cause of bacteremia and hospital-acquired infection, however a vaccine that prevents staphylococcal disease is currently not available. Two sortase-anchored surface proteins, IsdA and IsdB, have been identified as subunit vaccines that, following active immunization, protect experimental animals against intravenous challenge with staphylococci. Here we investigate the molecular basis of this immunity and report that, when passively transferred to naïve mice, purified antibodies directed against IsdA or IsdB protected against staphylococcal abscess formation and lethal intravenous challenge. When added to mouse blood, IsdA- or IsdB-specific antibodies did not promote rapid opsonophagocytic killing of wild-type staphylococci. Antibodies directed against IsdA interfered with heme-binding and IsdB antibodies perturbed the ability of this surface protein to bind hemoglobin. As the structural genes for isdA and isdB are required for heme-iron scavenging during the pathogenesis of infection, we hypothesize that IsdA and IsdB antibodies may at least in part provide protection against staphylococci by interfering with the pathogen's heme-iron scavenging mechanisms.

Genetic requirements for Staphylococcus aureus abscess formation and persistence in host tissues.

Staphylococcus aureus infections are associated with abscess formation and bacterial persistence; however, the genes that enable this lifestyle are not known. We show here that following intravenous infection of mice, S. aureus disseminates rapidly into organ tissues and elicits abscess lesions that develop over weeks but cannot be cleared by the host. Staphylococci grow as communities at the center of abscess lesions and are enclosed by pseudocapsules, separating the pathogen from immune cells. By testing insertional variants in genes for cell wall-anchored surface proteins, we are able to infer the stage at which these molecules function. Fibrinogen-binding proteins ClfA and ClfB are required during the early phase of staphylococcal dissemination. The heme scavenging factors IsdA and IsdB, as well as SdrD and protein A, are necessary for abscess formation. Envelope-associated proteins, Emp and Eap, are either required for abscess formation or contribute to persistence. Fluorescence microscopy revealed Eap deposition within the pseudocapsule, whereas Emp was localized within staphylococcal abscess communities. Antibodies directed against envelope-associated proteins generated vaccine protection against staphylococcal abscess formation. Thus, staphylococci employ envelope proteins at discrete stages of a developmental program that enables abscess formation and bacterial persistence in host tissues.