Somatic generation of immune diversity

Construction and Applications of Mammalian Cell-Based DNA-Encoded Peptide/Protein Libraries

DNA-encoded peptide/protein libraries are the starting point for protein evolutionary modification and functional peptide/antibody selection. Different display technologies, protein directed evolution, and deep mutational scanning (DMS) experiments employ DNA-encoded libraries to provide sequence variations for downstream affinity- or function-based selections. Mammalian cells promise the inherent post-translational modification and near-to-natural conformation of exogenously expressed mammalian proteins and thus are the best platform for studying transmembrane proteins or human disease-related proteins. However, due to the current technical bottlenecks of constructing mammalian cell-based large size DNA-encoded libraries, the advantages of mammalian cells as screening platforms have not been fully exploited. In this review, we summarize the current efforts in constructing DNA-encoded libraries in mammalian cells and the existing applications of these libraries in different fields.

Comparative Efficacy of Histrelin Acetate and hCG for Inducing Ovulation in Brazilian Northeastern Jennies (Equus africanus asinus)

The goal of this study was to compare the efficiency of histrelin acetate (GnRH analog) and human chorionic gonadotropin (hCG) to hasten ovulation in Brazilian Northeastern jennies (Equus africanus asinus). Thirty cycles of ten jennies were randomly assigned in one of the three groups: G0 (control group), saline; G1, 250 μg of histrelin acetate; G2, 2500 IU of hCG. Jennies were evaluated by transrectal palpation and ultrasonography, and had the administration of an ovulation-inducing agent when a follicle measuring between 29 and 32 mm of diameter was diagnosed. Jennies were monitored every 6 hours by transrectal ultrasonography until ovulation. The interval between prostaglandin administration and ovulation was lower (P < .05) in jennies from the G1 (145.2 ± 34.6 hours) and G2 (147.4 ± 27.3 hours) groups compared with the control cycle (220.0 ± 41.8 hours). Both treatments (G1, 41.15 ± 3.5 hours; G2, 37.8 ± 2.5 hours) also reduced (P < .05) the interval that jennies took to ovulate after the administration of the ovulation-inducing agent compared with the control (81.8 ± 28.8 hours). All jennies from G1 and G2 ovulated up to 48 hours after ovulation induction, whereas 100% of jennies in the control cycle ovulated later (>48 hours from the administration of saline). In conclusion, both histrelin acetate and hCG at the used dose are efficient ovulation-inducing agents in jennies promoting ovulation up to 48 hours after administration.

How does the immune system learn to distinguish between good and evil? The first definitive studies of T cell central tolerance and positive selection

Demonstration that immature CD4 + 8+ thymocytes contain T cell precursors that are subjected to positive and negative selection was the major step towards understanding how the adaptive immune system acquires the ability to distinguish foreign or abnormal (mutated or infected) self-cells from normal (healthy) cells. In the present review, the roles of TCR, CD4, CD8, and MHC molecules in intrathymic selection and some of the crucial experiments that contributed to the solution of the great immunological puzzle of self/nonself discrimination are described in an historical perspective. Recently, these experiments were highlighted by the immunological community by awarding the 2016 Novartis Prize for Immunology to Philippa Marrack, John Kappler, and Harald von Boehmer.

[IGoR: a tool for learning and simulating the random generation of antigen receptors]

Antigen receptors, which form the base of the adaptive immune system, are created stochastically by a DNA editing process called V(D)J recombination. As high-throughput sequencing enables to study the repertoire of these receptors, it is now possible to learn the probabilistic laws of this random process, and to use them to analyse receptors of interest, generate synthetic repertoires to create controls, or aid the identification of receptors that are specific to diseases, with possible applications for medical diagnostics. This article describes how these tasks can be performed using the IGoR software, which can learn statistical models from data, annotate existing sequences, or generate new synthetic ones with the same laws as the recombination process.

A common immunopathogenesis mechanism for infectious diseases: the protein-homeostasis-system hypothesis

It was once believed that host cell injury in various infectious diseases is caused solely by pathogens themselves; however, it is now known that host immune reactions to the substances from the infectious agents and/or from the injured host cells by infectious insults are also involved. All biological phenomena in living organisms, including biochemical, physiological and pathological processes, are performed by the proteins that have various sizes and shapes, which in turn are controlled by an interacting network within the living organisms. The author proposes that this network is controlled by the protein homeostasis system (PHS), and that the immune system is one part of the PHS of the host. Each immune cell in the host may recognize and respond to substances, including pathogenic proteins (PPs) that are toxic to target cells of the host, in ways that depend on the size and property of the PPs. Every infectious disease has its own set of toxic substances, including PPs, associated with disease onset, and the PPs and the corresponding immune cells may be responsible for the inflammatory processes that develop in those infectious diseases.

Incomplete TCR-β allelic exclusion accelerates spontaneous autoimmune arthritis in K/BxN TCR transgenic mice

Allelic exclusion of antigen receptor loci is a fundamental mechanism of immunological self-tolerance. Incomplete allelic exclusion leads to dual T-cell receptor (TCR) expression and can allow developing autoreactive αβ T lymphocytes to escape clonal deletion. Because allelic exclusion at the TCR-β locus is more stringent than at the TCR-α locus, dual TCR-β expression has not been considered a likely contributor to autoimmunity. We show here that incomplete TCR-β allelic exclusion permits developing thymocytes bearing the autoreactive, transgene-encoded KRN TCR to be positively selected more efficiently, thereby accelerating the onset of spontaneous autoimmune arthritis. Our findings highlight dual TCR-β expression as a mechanism that can enhance the maturation of autoreactive pathogenic T cells and lead to more rapid development of autoimmune disease.

Sexual dimorphism in immune response genes as a function of puberty

BACKGROUND

Autoimmune diseases are more prevalent in females than in males, whereas males have higher mortality associated with infectious diseases. To increase our understanding of this sexual dimorphism in the immune system, we sought to identify and characterize inherent differences in immune response programs in the spleens of male and female mice before, during and after puberty.

RESULTS

After the onset of puberty, female mice showed a higher expression of adaptive immune response genes, while males had a higher expression of innate immune genes. This result suggested a requirement for sex hormones. Using in vivo and in vitro assays in normal and mutant mouse strains, we found that reverse signaling through FasL was directly influenced by estrogen, with downstream consequences of increased CD8+ T cell-derived B cell help (via cytokines) and enhanced immunoglobulin production.

CONCLUSION

These results demonstrate that sexual dimorphism in innate and adaptive immune genes is dependent on puberty. This study also revealed that estrogen influences immunoglobulin levels in post-pubertal female mice via the Fas-FasL pathway.

Analysis of RAG expression by peripheral blood CD5+ and CD5- B cells of patients with childhood systemic lupus erythematosus

BACKGROUND

The assembly of immunoglobulin genes during B cell development in the bone marrow is dependent on the expression of recombination activating genes (RAG) 1 and 2. Recently, RAG expression in peripheral blood IgD+ B cells outside the bone marrow has been demonstrated and is associated with the development of autoimmune diseases.

OBJECTIVE

To investigate RAG expression in the CD5+ or CD5- IgD+ B cell compartment in childhood systemic lupus erythematosus (SLE).

METHODS

Using a combination of flow cytometric cell sorting and reverse transcriptase polymerase chain reaction analysis of cDNA libraries generated from individual cells, the expression of RAG, VpreB, and CD154 mRNA by individual peripheral blood B cells of three paediatric SLE patients was examined in detail.

RESULTS

While only one patient had a significantly increased frequency of RAG+ B cells in the CD5- B cell population, all patients showed higher frequencies of RAG+ B cells in the CD5+IgD+ B cell population. The frequency of RAG+ IgD+CD5+/- B cells was reduced during intravenous cyclophosphamide treatment. In healthy age matched children, RAG expressing IgD+ B cells were hardly detectable. Coexpression of RAG and VpreB or CD154 mRNA could only be found in SLE B cells.

CONCLUSIONS

RAG expression in peripheral blood B cells of SLE patients is particularly increased in the IgD+CD5+ B cell population. CD5+ and CD5- B cells in SLE have the potential to undergo receptor revision leading to the generation of high affinity pathogenic autoantibodies.

[Role of the innate immune response in sepsis]

Das angeborene („innate“) Immunsystem bekämpft erfolgreich den größten Teil unserer Infektionen, noch bevor das erworbene Immunsystem aktiviert wird. Genauere Kenntnisse über Wirkmechanismen des angeborenen Immunsystems lassen uns die Pathophysiologie systemischer Infektionen, wie der Sepsis, besser verstehen und dienen der Entwicklung neuer Therapiestrategien. Das angeborene Immunsystem ist für die erste Abwehrreaktion auf eine Infektion verantwortlich. Darüber hinaus aktiviert und interagiert es mit dem erworbenen Immunsystem. Wechselwirkungen werden über Immunzellen, wie Makrophagen und dendritische Zellen, sowie lösliche Faktoren, wie Zytokine, vermittelt. Aufgrund neuer Erkenntnisse aus Tiermodellen, die neben der Inflammation auch ein Fortschreiten der Bakterienabwehr berücksichtigen, mussten bisherige Erkenntnisse überprüft und korrigiert werden. Die Vorstellung von Sepsis als überwiegende „Überreaktion auf eine Entzündung“ wich neuen Theorien. Die Zellen des angeborenen Immunsystems erkennen Eindringlinge mit Hilfe spezieller Rezeptoren. Nach Rezeptorinteraktion führen intrazelluläre Signalkaskaden zur Zellaktivierung, durch die zahlreiche Zytokine und antimikrobielle Substanzen freigesetzt werden. Im Verlauf einer Sepsis kommt es durch verschiedene Regelkreise zu zunehmender Immunsuppression. Mit dem angeborenen Immunsystem verknüpft ist die Migration von Leukozyten in entzündetes Gewebe. Chemokine und Adhäsionsmoleküle übernehmen dabei Schlüsselrollen. Auch die Blutgerinnung ist mit dem angeborenen Immunsystem eng verzahnt. Immunzellen sezernieren „tissue factor“; dies führt über eine Kaskade u. a. zur Bildung von Thrombin. Dieses kann unter den besonderen Bedingungen der Sepsis eine disseminierte intravasale Gerinnung verursachen. Umgekehrt werden durch Thrombin auch Endothelzellen zur Freisetzung von Chemokinen und Adhäsionsmolekülen angeregt; dies stellt einen positiven „Feedback-Mechanismus“ für die angeborene Immunantwort dar. Neue Therapieansätze zur Sepsis versuchen diese Regelkreise zu durchbrechen und durch Blockade von Zytokinen, Rezeptoren oder durch Aktivierung immunstimulierender Systeme eine ausgewogene Reaktion des angeborenen Immunsystems ohne Suppression der antibakteriellen Funktion zu erzielen.

Adaptive value of polymorphism in intracellular self/not-self discrimination?

A microbial pathogen species can adapt to its host species to the extent that members of the host species are uniform. Loss of this uniformity would make it difficult for a pathogen species to transfer, from one member of the host species to another, what it had "learned" through selection of its members with advantageous mutations. The existence of major histocompatibility complex (MHC) polymorphism indicates that non-uniformity within a species is an effective host defence strategy. By virtue of this molecular discontinuity among its members the host species can "present a moving target" to the pathogen. Many proteins other than MHC proteins show polymorphism - a phenomenon which has suggested that mutations in regions of protein molecules which do not affect overt function are neutral. However, in the context of the author's differential aggregation theory of intracellular self/not-self discrimination as previously applied to the problem of the antigenicity of cancer cells, such polymorphism should serve for the recruitment of subsets of self-antigens into the antigenic repertoire of an infected cell. These would act as "intracellular antibodies" by virtue of their weak, but specific, aggregation with pathogen proteins. Peptides from the self-antigens, as well as (or instead of) those from the antigens of the pathogen, would then serve as targets for attack by cytotoxic T cells. Thus, polymorphism of intracellular proteins should be of adaptive value, serving to amplify and individualize the immune response to intracellular pathogens.

Immunology of trauma

Systemic inflammation involves a large number of mediators and effector mechanisms. One approach to understanding systemic inflammation is to interpret the nature of the response based on the effector mechanisms that are observed. An alternative approach is to consider these effector responses in the context of our current understanding of immunoregulation. The aim of this article is to provide an overview of the immune response and discuss the mechanisms of immunoregulation in order to provide non-immunologists with a framework for understanding the normal and aberrant immune responses that can be precipitated by major trauma. The clinical manifestations of the inflammatory response to major trauma resemble those observed after other significant insults (surgery, burns, and pancreatitis). Furthermore, the clinical manifestations, changes in serum proteins, and pattern of immune activation point to the presence of infection, yet proof of a contribution by infection to the pathogenesis by infection remains elusive. Although inflammation dominates the early phase of the response, there is often evidence of a paradoxical combination of inflammation and immunosuppression later on. Consideration of the proinflammatory cascades, and the contribution of the innate immune system, helps explain why the clinical picture after major trauma may resemble other clinical states. It also explains the counter-regulatory response, which normally acts to downregulate inflammation, but may cause immunosuppression in the face of persistent inflammation after major trauma.

In vitro evolution of a T cell receptor with high affinity for peptide/MHC

T cell receptors (TCRs) exhibit genetic and structural diversity similar to antibodies, but they have binding affinities that are several orders of magnitude lower. It has been suggested that TCRs undergo selection in vivo to maintain lower affinities. Here, we show that there is not an inherent genetic or structural limitation on higher affinity. Higher-affinity TCR variants were generated in the absence of in vivo selective pressures by using yeast display and selection from a library of Valpha CDR3 mutants. Selected mutants had greater than 100-fold higher affinity (K(D) approximately 9 nM) for the peptide/MHC ligand while retaining a high degree of peptide specificity. Among the high-affinity TCR mutants, a strong preference was found for CDR3alpha that contained Pro or Gly residues. Finally, unlike the wild-type TCR, a soluble monomeric form of a high-affinity TCR was capable of directly detecting peptide/MHC complexes on antigen-presenting cells. These findings prove that affinity maturation of TCRs is possible and suggest a strategy for engineering TCRs that can be used in targeting specific peptide/MHC complexes for diagnostic and therapeutic purposes.

Distinct signals mediate maturation and allelic exclusion in lymphocyte progenitors

Successful in-frame rearrangement of immunoglobulin heavy chain genes or T cell antigen receptor (TCR) beta chain genes in lymphocyte progenitors results in formation of pre-BCR and pre-TCR complexes. These complexes signal progenitor cells to mature, expand in cell number, and suppress further rearrangements at the immunoglobulin heavy chain or TCRbeta chain loci, thereby ensuring allelic exclusion. We used transgenic expression of a constitutively active form of c-Raf-1 (Raf-CAAX) to demonstrate that activation of the Map kinase pathway can stimulate both maturation and expansion of B and T lymphocytes, even in the absence of pre-TCR or pre-BCR formation. However, the same Raf signal did not mediate allelic exclusion. We conclude that maturation of lymphocyte progenitors and allelic exclusion require distinct signals.

Novel electrophoretic protocol for collection of mutations in the lambda light chain immunoglobulin gene in a human B-lymphoblastoid cell strain

Spontaneous and chemically induced mutation was examined in the lambda light chain immunoglobulin gene in a human B-lymphoblastoid cell strain (T5-1). The hemizygous lambda gene is a unique mutational target gene which codes for a protein that is both expressed on the cell membrane and secreted. Mutations in the lambda gene were detected by analysis of western blots of isoelectric focusing gel electrophoresis of T5-1 cell conditioned culture medium. None of 5,841 individual clones established from vehicle-exposed populations had detectable variations in the isoelectric banding pattern of the constitutively secreted lambda immunoglobulin protein. In contrast, 113 of 6,128 clonal populations established from N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-exposed populations exhibited stable variations in expression of the lambda immunoglobulin: isoelectric variants (n = 3) and non-secretors (n = 110). MNNG-induced mutations in the lambda gene, which resulted in lambda immunoglobulin proteins with altered isoelectric points (pIs), occurred at a frequency of no less than 4.9 x 10(-4) mutations/cell, indicating the mature rearranged lambda immunoglobulin gene is comparably sensitive to carcinogen induced mutation as other human autosomal target genes. Approximately one-half of the MNNG-induced non-secretor mutant clones lacked lambda mRNA while one-half maintained constitutive transcription and expression of the lambda immunoglobulin on the cell surface, demonstrating that carcinogen damage interdicted gene function at multiple points.

Chimeric T cell receptor-immunoglobulin molecules: function and applications

The antigen-specific receptors on T and B cells are related by sequence similarities, mechanisms for the generation of diversity, and a common protein domain structure. In contrast, the form of antigen recognition for T- and B-cell antigen receptors is entirely different. Whereas the B cell antigen receptor, i.e., membrane-bound immunoglobulin (Ig), has the potential to recognize a vast diversity of chemical determinants, the T cell antigen receptor (TCR) invariably recognizes oligomeric peptides bound to major histocompatibility complex molecules. A question is whether the variable domains of the TCR and Ig are similar in structure, and if so, can they be substituted one for the other. Recent experiments show that, in some combinations, the variable region of Ig can substitute for the variable region of a TCR, and convey, to a reactive T lymphocyte, the antigen specificity of an Ig molecule. This type of receptor engineering may have interesting applications in disease therapy.

Early detection of antibody to human immunodeficiency virus type 1 by using an antigen conjugate immunoassay correlates with the presence of immunoglobulin M antibody

Sequential plasma samples obtained from 16 individuals who seroconverted were tested for the presence of antibody to human immunodeficiency virus type 1 (HIV-1) by an antigen conjugate enzyme immunoassay (EIA) and a conventional antibody conjugate assay. In 11 of these individuals, the antigen conjugate assay detected antibody to HIV-1 2 to 11 days (mean, 5.5 days) earlier than the antibody conjugate assay. In 11 individuals, HIV-1 p24 antigen was detected a median of 6.5 days (range, 3 to 14 days) prior to positivity by the antigen conjugate EIA. Using class-specific probes, we determined the profiles of immunoglobulin M (IgM), IgG, and IgA antibodies for each individual and correlated these profiles with the EIA signals from both assays. In general, the appearance of IgM exhibited a peak at about 1 week postseroconversion, which was followed by gradually declining levels. Absorbance levels for IgG antibody, however, rose steadily and reached a plateau after 3 to 5 weeks. The levels of IgA were generally low and variable. In contrast to the progressive increase in EIA absorbance observed by the antibody conjugate assay, the antigen conjugate assay displayed a rapid early rise in absorbance which generally coincided with the transient expression of IgM antibody. The subsequent gradual increase coincided with rising levels of IgG. Because the configuration of the antigen conjugate EIA allows for an increased sensitivity for IgM compared with that for other classes of immunoglobulins, these results suggest that earlier detection of antibody to HIV-1 is due to the detection of IgM antibody during the early phase of seroconversion.