Recent advances have provided substantial insight into the maintenance of mucosal immunity and the pathogenesis of inflammatory bowel disease. Cellular programs responsible for intestinal homeostasis use diverse intracellular and intercellular networks to promote immune tolerance, inflammation or epithelial restitution. Complex interfaces integrate local host and microbial signals to activate appropriate effector programs selectively and even drive plasticity between these programs. In addition, genetic studies and mouse models have emphasized the role of genetic predispositions and how they affect interactions with microbial and environmental factors, leading to pro-colitogenic perturbations of the host-commensal relationship.

Genetics and pathogenesis of inflammatory bowel disease

Sera of camelids contain both conventional heterotetrameric antibodies and unique functional heavy (H)-chain antibodies (HCAbs). The H chain of these homodimeric antibodies consists of one antigen-binding domain, the VHH, and two constant domains. HCAbs fail to incorporate light (L) chains owing to the deletion of the first constant domain and a reshaped surface at the VHH side, which normally associates with L chains in conventional antibodies. The genetic elements composing HCAbs have been identified, but the in vivo generation of these antibodies from their dedicated genes into antigen-specific and affinity-matured bona fide antibodies remains largely underinvestigated. However, the facile identification of antigen-specific VHHs and their beneficial biochemical and economic properties (size, affinity, specificity, stability, production cost) supported by multiple crystal structures have encouraged antibody engineering of these single-domain antibodies for use as a research tool and in biotechnology and medicine.

Nanobodies: Natural Single-Domain Antibodies

Neutrophils are the most abundant white blood cells in circulation, and patients with congenital neutrophil deficiencies suffer from severe infections that are often fatal, underscoring the importance of these cells in immune defense. In spite of neutrophils' relevance in immunity, research on these cells has been hampered by their experimentally intractable nature. Here, we present a survey of basic neutrophil biology, with an emphasis on examples that highlight the function of neutrophils not only as professional killers, but also as instructors of the immune system in the context of infection and inflammatory disease. We focus on emerging issues in the field of neutrophil biology, address questions in this area that remain unanswered, and critically examine the experimental basis for common assumptions found in neutrophil literature.

Neutrophil Function: From Mechanisms to Disease

The expanding scope of antimicrobial peptide structures and their modes of action.

Surface tissues of the body such as the skin and intestinal tract are in direct contact with the external environment and are thus continuously exposed to large numbers of microorganisms. To cope with the substantial microbial exposure, epithelial surfaces produce a diverse arsenal of antimicrobial proteins that directly kill or inhibit the growth of microorganisms. In this Review, we highlight new advances in our understanding of how epithelial antimicrobial proteins protect against pathogens and contribute to microbiota-host homeostasis at the skin and gut mucosae. Further, we discuss recent insights into the regulatory mechanisms that control antimicrobial protein expression. Finally, we consider how impaired antimicrobial protein expression and function can contribute to disease.

Epithelial antimicrobial defence of the skin and intestine

Human epithelia are permanently challenged by bacteria and fungi, including commensal and pathogenic microbiota. In the gut, the fraction of strict anaerobes increases from proximal to distal, reac ...

Reduction of disulphide bonds unmasks potent antimicrobial activity of human β-defensin 1

An unfolded CH1 domain controls the assembly and secretion of IgG antibodies.

Folding intermediates play a key role in deﬁning protein foldingand assembly pathways as well as those of misfolding and aggre-gation.Yet,duetotheirtransientnature,theyarepoorlyaccessibleto high-resolution techniques. Here, we made use of the intrinsi-cally slow folding reaction of an antibody domain to characterizeits major folding intermediate in detail. Furthermore, by a singlepoint mutation we were able to trap the intermediate in equilib-rium and characterize it at atomic resolution. The intermediateexhibits the basic -barrel topology, yet some strands are dis-torted. Surprisingly, two short strand-connecting helices con-served in constant antibody domains assume their completelynative structure already in the intermediate, thus providing ascaffold for adjacent strands. By transplanting these helical ele-ments into

The structure of a folding intermediate provides insight into differences in immunoglobulin

Folding intermediates play a key role in defining protein folding and assembly pathways as well as those of misfolding and aggregation. Yet, due to their transient nature, they are poorly accessible to high-resolution techniques. Here, we made use of the intrinsically slow folding reaction of an antibody domain to characterize its major folding intermediate in detail. Furthermore, by a single point mutation we were able to trap the intermediate in equilibrium and characterize it at atomic resolution. The intermediate exhibits the basic β-barrel topology, yet some strands are distorted. Surprisingly, two short strand-connecting helices conserved in constant antibody domains assume their completely native structure already in the intermediate, thus providing a scaffold for adjacent strands. By transplanting these helical elements into β2-microglobulin, a highly homologous member of the same superfamily, we drastically reduced its amyloidogenicity. Thus, minor structural differences in an intermediate can shape the folding landscape decisively to favor either folding or misfolding.

https://www.pnas.org/content/pnas/105/36/13373.full.pdf

Sandra Groscurth

Papers

Reduction of disulphide bonds unmasks potent antimicrobial activity of human β-defensin 1

An unfolded CH1 domain controls the assembly and secretion of IgG antibodies.

The structure of a folding intermediate provides insight into differences in immunoglobulin

The structure of a folding intermediate provides insight into differences in immunoglobulin amyloidogenicity