Erratum to: "The Chemical Characterization of the Pneumococcal Transforming Principle. Pathogens and Immunity. 2024;8(2):177-178. doi: 10.20411/pai.v8i2.687"

[This corrects the article DOI: 10.20411/pai.v8i2.687.].

Historical Highlight: The Chemical Characterization of the Pneumococcal Transforming Principle

The editors of Pathogens and Immunity are commemorating this month, the 80th anniversary of the publication of the landmark article by Oswald Avery, Colin MacLeod, and Maclyn McCarty in the Journal of Experimental Medicine on February 1, 1944 [1]. The study by Avery et al determined with extraordinary rigor the chemical nature of the so-called transforming principle inferred to exist by Frederick Griffith based on experiments he published in 1928. 

Vishva Dixit Shares Insights on His Early Influences, Research Career, Key Findings, and What it Takes to Be Successful in Science

In this interview, Vishva Dixit, MD, talks with Neil S. Greenspan, MD, PhD, senior editor of Pathogens and Immunity aboutwhat his career in science has revealed about biology in humans, but also what it has revealed about how to be successful in science. Dr. Dixit is a world-famous immunologist and biochemist who has made major contributions to the study of innate immunity in general and particularly to understanding inflammasome activation. He is vice president and senior fellow in physiological chemistry at Genentech.

Epitopes, paratopes, and other topes 30 years on: Understanding what we are talking about

The question of which protein antigens, such as HLA class I or class II molecules, will bind, and how well, to a given antibody is often assumed to depend exclusively on the details of protein surface structure. These structures are usually based on static models resulting from X-ray crystallography. While these notions are useful, the ultimate causal factors determining how well a given antigen binds a given antibody are based in thermodynamics and can include atomic mobility and the time-varying conformations of proteins. In this article, fundamental biophysical principles of antibody-antigen interaction are discussed, concepts critical for a deeper understanding of the pertinent molecular phenomena are highlighted, and common misunderstandings are identified and debunked.

Pandemics and the English Language: Concepts Critical for Conversing About COVID-19

We consider the multiple senses of several key terms that are used to discuss the ongoing COVID-19 pandemic and clarify meanings of the corresponding concepts. Topics addressed include: 1) the meaning of immunity to an infectious agent in varying medical and scientific contexts, 2) the scientific factors that influenced the rapid generation and clinical implementation of safe and effective vaccines for COVID-19, 3) the difference between mutational abrogation of reactivity with B- or T-cell antigen receptors (immune escape) versus active interference with host immune mechanisms mediated by gene products encoded within the genome of the infectious agent (immune evasion), 4) the different ways by which the COVID-19 pandemic has “caused” deaths, and 5) briefly, the challenge of precisely defining the term pathogen.

Genes, Heritability, 'Race', and Intelligence: Misapprehensions and Implications

The role of genetics in determining measured differences in mean IQ between putative racial groups has been a focus of intense discussion and disagreement for more than 50 years. While the last several decades of research have definitively demonstrated that genetic variation can influence measures of cognitive function, the inferences drawn by some participants in the controversy regarding the implications of these findings for racial differences in cognitive ability are highly dubious. Of equal importance, there is no compelling scientific rationale for focusing on and devoting substantial effort to determining mean differences in intelligence or other cognitive functions between groups with incompletely defined and dynamic (and therefore not definitively definable) boundaries.

A Disquisition on MHC Restriction and T Cell Recognition in Five Acts

The seminal discovery in the early 1970s, credited to Peter Doherty and Rolf Zinkernagel, of major histocompatibility complex (MHC) restriction exhibited by cytotoxic T cells represented a major conceptual advance in understanding antigen recognition by conventional T cells. This advance also led to other major new insights into the ontogeny and immunobiology of T cells and catalyzed a renaissance in viral immunology. In this commentary in honor of Peter Doherty, I offer five brief reflections on different aspects of the phenomenon of MHC restriction and the process by which it was discovered and explained. In the first of these sections, I offer a reinterpretation of MHC restriction that reframes the constraints on self-MHC recognition in terms of the probabilities of recognizing a given nominal antigen peptide in the context of an MHC molecule that is nonself on the basis of differing in amino acid sequence from the self-restriction element at one or more positions. Subsequent sections address: (i) the ways in which general ideas, developed subsequent to the discovery of MHC restriction, about the intricacies of antigen recognition by antibodies apply to T cell receptors binding to MHC/peptide complexes; (ii) how to reconcile the existence of MHC restriction with the impressive magnitude of T cell responses to nonself MHC antigens; (iii) the possible relevance to MHC restriction and immune system function of ideas from mathematical logic that relate to the consequences of self-reference; and (iv) the implications for the philosophy of science of MHC restriction and the processes of its discovery and acceptance within the immunology research community.

Relapse Following Allogeneic Hematopoietic Cell Transplantation for Acute Myeloid Leukemia Apparently Due to Somatic Cell Evolution via Epigenetic Variation and Immune Selection

In this brief commentary, I discuss a recently published study that documents the role of immune escape in relapse of acute myeloid leukemia (AML) after hematopoietic cell transplantation (HCT). Of particular interest, the mechanism identified by the authors for the ability of the malignant cells to evade destruction by host T cells is the loss of cell surface expression of HLA class II molecules based on processes other than mutation. The authors labeled this mechanism for altered cell surface display of HLA class II antigens “epigenetic.”

This study should be of strong interest for immunologists, oncologists and even specialists in infectious diseases for several reasons. First, the results extend the range of examples for which epigenetic mechanisms can play a critical role in resistance to therapy in oncology or infectious disease. Second, findings relating to decreased cell surface display of HLA class II molecules motivate investigation of novel approaches using cytokines to increase the numbers of HLA class II proteins on malignant myeloid cell membranes and reduce the extent of immune escape by these cells. Third, the data presented suggest experimental directions intended to clarify detailed molecular mechanisms underlying the cases of AML post-HCT relapse and raise questions relating to why some mechanisms of somatic cell evolution and not others are operative in different clinical settings.

Autism, evolution, and the inadequacy of 'spectrum'

Lay Summary: Individuals diagnosed with autism display variation in many traits, such as interest and ability in social interaction or resistance to change. Referring to this variation as a 'spectrum', defined as a range of values along an axis, understates the extent of such variation and can foster incorrect inferences. In psychiatry, the currently accepted term for a developmental disability characterized by variably impaired social and communicative skills, repetitive behaviors, and restricted interests is "autism spectrum disorder." "Spectrum," typically refers to values of a variable distributed along a single dimension, incorrectly suggesting people with autism can be simply ranked as more or less 'autistic.' In fact, there are multiple traits that pertain to autism and that can vary somewhat independently, in part due to the evolutionary mechanisms that give rise to risk alleles. Therefore, a new and more accurate clinical descriptor should be adopted. I propose: autism-related disorders (ARD).

Celebrating More Than a Century of Research on Antibodies: Affirmation Through Negation via Complex Formation

In this brief commentary, I highlight the remarkable properties of antibodies (also known as immunoglobulins) revealed by more than 100 years of biomedical research. Since antibodies can be elicited through one or another means against almost any molecule or macromolecule, the universe of antibodies represents a sort of molecular mirror for the totality of molecules that make life possible. Consequently, as recounted below, antibodies play a role in almost every aspect of medicine and biomedical research.

"Infectious Supercarelessness" in Discussing Antibiotic-Resistant Bacteria

Many bacterial pathogens are exhibiting resistance to increasing numbers of antibiotics making it much more challenging to treat the infections caused by these microbes. In many reports in the media and perhaps even in discussions among physicians and biomedical scientists, these bacteria are frequently referred to as “bugs” with the prefix “super” appended. This terminology has a high potential to elicit unjustified inferences and fails to highlight the broader evolutionary context. Understanding the full range of biological and evolutionary factors that influence the spread and outcomes of infections is critical to formulating effective individual therapies and public health interventions. Therefore, more accurate terminology should be used to refer these multidrug-resistant bacteria.

Ig Constant Region Effects on Variable Region Structure and Function

The adaptive humoral immune response is responsible for the generation of antimicrobial proteins known as immunoglobulin molecules or antibodies. Immunoglobulins provide a defense system against pathogenic microbes and toxins by targeting them for removal and/or destruction. Historically, antibodies have been thought to be composed of distinct structural domains known as the variable and constant regions that are responsible for antigen binding and mediating effector functions such as opsonization and complement activation, respectively. These domains were thought to be structurally and functionally independent. Recent work has revealed however, that in some families of antibodies, the two regions can influence each other. We will discuss the body of work that led to these observations, as well as the mechanisms that have been proposed to explain how these two different antibody regions may interact in the function of antigen binding.

Protein thermodynamics and the cognitive ecology of biomedicine

Assessments of scientific contributions critically influence decisions about grant funding and academic promotion. Unfortunately, there is a tendency for more junior and less assertive individuals to receive less credit than deserved. Acknowledgement of the complexity of relationships among researchers and the different modes of contributing to scientific progress could improve this situation. The thermodynamics of ligand binding is arguably among the most quantitative and empirically validated theoretical frameworks that permit precise apportionment of "credit" to multiple interacting entities that collectively account for a biologically relevant outcome, in this case, receptor-ligand complex formation. The process for assigning credit for research advances to individual researchers might benefit from emulating this thermodynamic thought process by recognizing that contributions of equal quantitative significance can be of different types and can originate through indirect effects. If the hypothesis that some categories of research contribution are frequently under-valued is correct, then calling attention to this state of affairs and providing an alternative way to conceptualize the task of credit attribution has the potential to begin altering the status quo. A beginning step to improving our credit attribution process would be the empirical investigation of accounts of contributions to particular scientific advances from all research team members.

Clinical consequences of human evolution shaped by cultural trends

Recent reports suggest that increased human population size, decreased negative selection pertaining to some phenotypes and associated genotypes and a possibly increased de novo mutation burden for newborns that relates to paternal age at conception are contributing to an expansion of human genetic diversity. Some of this diversity can be expected to contribute to disease. Because all of the preceding diversity-enhancing factors are to a significant degree consequences of cultural developments, it can be argued that the future clinical burden of the human population will be shaped in part by a human evolutionary trajectory substantially influenced by culturally mediated effects on the number of mutations in the gene pool and on the intensity of selection on some of the phenotypes associated with new genetic variants.

IgG3 deficiency extends lifespan and attenuates progression of glomerulonephritis in MRL/lpr mice

Background

Antibodies of the IgG3 subclass have been implicated in the pathogenesis of the spontaneous glomerulonephritis observed in mice of the MRL/MpJ-Tnfrsf6lpr (MRL/lpr) inbred strain which have been widely studied as a model of systemic lupus erythematosus We have produced IgG3-deficient (-/-) mice with the MRL/lpr genetic background to determine whether IgG3 antibodies are necessary for or at least contributory to MRL/lpr-associated nephritis.

Results

The gamma3 genotype (+/+ vs. +/- vs. -/-) did not appear to significantly affect serum titers of IgG auto-antibodies specific for double-stranded DNA (dsDNA) or α-actinin. However, while substantial serum titers of IgG3 auto-antibodies specific for double-stranded DNA (dsDNA) or α-actinin were seen in gamma3 +/+ mice, somewhat lower serum titers of these IgG3 auto-antibodies were found in gamma3 +/- mice, and gamma3 -/- mice exhibited baseline concentrations of these auto-antibodies. Analysis of immunoglobulins eluted from snap-frozen kidneys obtained from mice of all three gamma3 genotypes at ~18 weeks of age revealed much higher quantities of IgG in the kidneys from gamma3 +/+ than gamma3 -/- mice, and most IgG eluted from +/+ mice was IgG3. The serum creatinine levels in gamma3 +/+ mice substantially exceeded those of age-matched gamma3 -/- mice after ~21 weeks of age. Histopathological examination of kidneys from mice sacrificed at pre-determined ages also revealed more extensive glomerulosclerosis in gamma3 +/+ or +/- mice than in -/- mice beginning at 21 weeks of age. Survival analysis for IgG3-deficient and IgG3-producing MRL/lpr mice revealed that gamma3 -/- mice lived significantly longer (p = 0.0006) than either gamma3 +/- or +/+ mice. Spontaneous death appeared to be due to irreversible renal failure, because > 85% of glomeruli in kidneys from mice that died spontaneously were obliterated by glomerulosclerosis.

Conclusions

The available evidence suggests that IgG3 deficiency partially protects MRL/lpr mice against glomerulonephritis-associated morbidity and mortality by slowing or arresting the progression to glomerulosclerosis.

Reviewers

This article was reviewed by Pushpa Pandiyan, Irun Cohen, and Etienne Joly.

Enhanced immunogenicity of pneumococcal surface adhesin A (PsaA) in mice via fusion to recombinant human B lymphocyte stimulator (BLyS)

Background

B lymphocyte stimulator (BLyS) is a member of the tumor necrosis factor superfamily of ligands that mediates its action through three known receptors. BLyS has been shown to enhance the production of antibodies against heterologous antigens when present at elevated concentrations, supporting an immunostimulatory role for BLyS in vivo.

Methods

We constructed a fusion protein consisting of human BLyS and Pneumococcal Surface Adhesin A (PsaA) and used this molecule to immunize mice. The immunostimulatory attributes mediated by BLyS in vivo were evaluated by characterizing immune responses directed against PsaA.

Results

The PsaA-BLyS fusion protein was able to act as a co-stimulant for murine spleen cell proliferation induced with F(ab')₂ fragments of anti-IgM in vitro in a fashion similar to recombinant BLyS, and immunization of mice with the PsaA-BLyS fusion protein resulted in dramatically elevated serum antibodies specific for PsaA. Mice immunized with PsaA admixed with recombinant BLyS exhibited only modest elevations in PsaA-specific responses following two immunizations, while mice immunized twice with PsaA alone exhibited undetectable PsaA-specific serum antibody responses. Sera obtained from PsaA-BLyS immunized mice exhibited high titers of IgG1, IgG2a, IgG2b, and IgG3, but no IgA, while mice immunized with PsaA admixed with BLyS exhibited only elevated titers of IgG1 following two immunizations. Splenocytes from PsaA-BLyS immunized mice exhibited elevated levels of secretion of IL-2, IL-4 and IL-5, and a very modest but consistent elevation of IFN-γ following in vitro stimulation with PsaA. In contrast, mice immunized with either PsaA admixed with BLyS or PsaA alone exhibited modestly elevated to absent PsaA-specific recall responses for the same cytokines. Mice deficient for one of the three receptors for BLyS designated Transmembrane activator, calcium modulator, and cyclophilin ligand [CAML] interactor (TACI) exhibited attenuated PsaA-specific serum antibody responses following immunization with PsaA-BLyS relative to wild-type littermates. TACI-deficient mice also exhibited decreased responsiveness to a standard pneumococcal conjugate vaccine.

Conclusion

This study identifies covalent attachment of BLyS as a highly effective adjuvant strategy that may yield improved vaccines. In addition, this is the first report demonstrating an unexpected role for TACI in the elicitation of antibodies by the PsaA-BLyS fusion protein.

Reviewers

This article was reviewed by Jonathan Yewdell, Rachel Gerstein, and Michael Cancro (nominated by Andy Caton).

Attributing functions to genes and gene products

A major focus of modern biochemical, biophysical and cell biological research is the attribution of function to elements of structure: gene products, genes and higher-order cellular structures. Misunderstandings and controversies can arise in connection with such assignments, in part because of the logical complexity inherent in the relating of structure to function and the failure to distinguish clearly among the different senses in which function can be imputed to elements of structure. I explore distinct ways in which functions are connected to structures and factors that contribute to the context-dependence of such associations so that the multiple senses of function can be made explicit.

PrP conformational transitions alter species preference of a PrP-specific antibody

The epitope of the 3F4 antibody most commonly used in human prion disease diagnosis is believed to consist of residues Met-Lys-His-Met (MKHM) corresponding to human PrP-(109-112). This assumption is based mainly on the observation that 3F4 reacts with human and hamster PrP but not with PrP from mouse, sheep, and cervids, in which Met at residue 112 is replaced by Val. Here we report that, by brain histoblotting, 3F4 did not react with PrP of uninfected transgenic mice expressing elk PrP; however, it did show distinct immunoreactivity in transgenic mice infected with chronic wasting disease. Compared with human PrP, the 3F4 reactivity with the recombinant elk PrP was 2 orders of magnitude weaker, as indicated by both Western blotting and surface plasmon resonance. To investigate the molecular basis of these species- and conformer-dependent preferences of 3F4, the epitope was probed by peptide membrane array and antigen competition experiments. Remarkably, the 3F4 antibody did not react with MKHM but reacted strongly with KTNMK (corresponding to human PrP-(106-110)), a sequence that is also present in cervids, sheep, and cattle. 3F4 also reacted with elk PrP peptides containing KTNMKHV. We concluded that the minimal sequence for the 3F4 epitope consists of residues KTNMK, and the species- and conformer-dependent preferences of 3F4 arise largely from the interactions between Met(112) (human PrP) or Val(115) (cervid PrP) and adjacent residues.

Cohen's Conjecture, Howard's Hypothesis, and Ptashne's Ptruth: an exploration of the relationship between affinity and specificity

Both affinity and specificity for ligands directly influence the functions of biological macromolecules. Some investigators assume that there is a consistent relationship between the affinity of a receptor molecule for its cognate ligand(s) and the specificity of that same receptor (affinity for cognate versus non-cognate ligands). However, analysis of the range of physical factors that account for changes in affinity, in any particular direction and to any particular degree, of a receptor for a cognate ligand suggests strongly that such factors can have disparate effects on the affinities of the receptor for different non-cognate ligands. Therefore, there can be no simple relationship between affinity and specificity as defined by relative binding of the receptor to cognate and non-cognate ligands.

Decreased expression of tumor necrosis factor family receptors involved in humoral immune responses in preterm neonates

Neonates have an increased rate of infection with encapsulated bacteria compared with older children and adults because of diminished antibody responses to T-independent (TI) antigens such as bacterial polysaccharides. Because the interactions of tumor necrosis factor (TNF) family ligands BAFF and APRIL with the TNF family receptors (TNFRs) TACI, BCMA, and BAFF-R are crucial to TI antibody responses, we measured the expression of these receptors on adult and cord blood-derived term and preterm neonatal B cells. Preterm neonatal B cells expressed less TACI, BCMA, and BAFF-R compared with adult B cells and had significantly less proliferation compared with adult B cells after stimulation with human recombinant BAFF and anti-IgM in an assay in which TACI-Fc fusion protein inhibits B-cell proliferation. In addition, neonatal dendritic cells had diminished expression of B7-1, B7-2, and CD40 compared with adult cells. Finally, neonatal B cells, particularly preterm B cells, exhibited markedly decreased production of IgG and IgA in response to CD40L and IL-10. Overall, this study shows that maturational delay in TNFR expression particularly by preterm neonatal B cells may interfere with effective antibody responses to TI antigens, cognate T- and B-cell interactions and normal isotype switching.

Streptozocin-induced diabetes accelerated by B cells transgenic for immunoglobulin heavy chain recognizing N-acetyl-D-glucosamine (130.35)

To determine mechanisms of autoreactive B cell selection and their involvement in the pathogenesis of autoimmune diseases, we generated a novel immunoglobulin (Ig) transgenic (Tg) mouse line, HGAC 39. In these mice, B cells express an Ig heavy chain with specificity for N-acetyl-D-glucosamine (GlcNAc) found on the cell wall of Group A Streptococcus (GAS). Tg B cells responded to iv immunization by migrating from the marginal zone to the TB border, and expanding and differentiating to plasmablasts at extrafollicular foci. Since GlcNAcylated proteins are abundant within eukaryotic cells, we hypothesized that B cells with anti-GlcNAc specificities contribute to autoimmune disease by presenting GlcNAc-modified proteins to diabetogenic CD4+ and CD8+ T cells. We induced autoimmune diabetes in Tg C57BL/6 male mice with multiple low doses of streptozocin (STZ), a β cell-specific toxin that increases GlcNAcylation of intracellular proteins, and demonstrated that the presence of HGAC 39 B cells accelerates the onset of hyperglycemia and pancreatic infiltration by HGAC 39 B cells, CD4+, and CD8+ T cells. These changes were not accompanied by increases in anti-GlcNAc plasma cells or serum antibodies. Taken together, our data suggest that HGAC 39 B cells that respond to GAS immunization can also contribute to STZ-induced diabetes by mechanisms other than autoantibody secretion.

Conceptualizing immune responsiveness

Communicating about and comprehending immune responses and immunity will be facilitated by greater attention to semantic precision and consistency and increased willingness to engage with the full dimensionality and quantitative nature of immunological phenomena.

Complement Component C3d-Antigen Complexes Can Either Augment or Inhibit B Lymphocyte Activation and Humoral Immunity in Mice Depending on the Degree of CD21/CD19 Complex Engagement

C3d can function as a molecular adjuvant by binding CD21 and thereby enhancing B cell activation and humoral immune responses. However, recent studies suggest both positive and negative roles for C3d and the CD19/CD21 signaling complex in regulating humoral immunity. To address whether signaling through the CD19/CD21 complex can negatively regulate B cell function when engaged by physiological ligands, diphtheria toxin (DT)-C3d fusion protein and C3dg-streptavidin (SA) complexes were used to assess the role of CD21 during BCR-induced activation and in vivo immune responses. Immunization of mice with DT-C3d3 significantly reduced DT-specific Ab responses independently of CD21 expression or signaling. By contrast, SA-C3dg tetramers dramatically enhanced anti-SA responses when used at low doses, whereas 10-fold higher doses did not augment immune responses, except in CD21/35-deficient mice. Likewise, SA-C3dg (1 microg/ml) dramatically enhanced BCR-induced intracellular calcium concentration ([Ca2+]i) responses in vitro, but had no effect or inhibited [Ca2+]i responses when used at 10- to 50-fold higher concentrations. SA-C3dg enhancement of BCR-induced [Ca2+]i responses required CD21 and CD19 expression and resulted in significantly enhanced CD19 and Lyn phosphorylation, with enhanced Lyn/CD19 associations. BCR-induced CD22 phosphorylation and Src homology 2 domain-containing protein tyrosine phosphatase-1/CD22 associations were also reduced, suggesting abrogation of negative regulatory signaling. By contrast, CD19/CD21 ligation using higher concentrations of SA-C3dg significantly inhibited BCR-induced [Ca2+]i responses and inhibited CD19, Lyn, CD22, and Syk phosphorylation. Therefore, C3d may enhance or inhibit Ag-specific humoral immune responses through both CD21-dependent and -independent mechanisms depending on the concentration and nature of the Ag-C3d complexes.

Genetic fusion of three tandem copies of murine C3d sequences to diphtheria toxin fragment B elicits a decreased fragment B-specific antibody response

Previous studies have demonstrated that the covalent modification of target protein and polysaccharide antigens with the activated complement product C3d results in dramatically enhanced immunogenicity of the target antigens. In this paper, we describe our attempts to enhance the immunogenicity of the non-toxic B fragment of diphtheria toxin (DT-B) by genetic fusion to polypeptides derived from the C3d coding sequence. Contrary to expectations, we found that the antibody responses elicited by immunizing mice with DT-B genetically linked to three tandem copies of C3d-derived sequences were markedly reduced relative to the antibody responses elicited by immunizing mice with DT-B alone. These results demonstrate levels of complexity in the immunomodulatory effects of the complement system that were not apparent in earlier reports on the adjuvant effects of C3d administered to mice as genetic fusions to target antigens, such as hen egg lysozyme, human immunodeficiency virus (HIV) gp120 or influenza virus hemaglutinnin. The data presented herein suggest that C3d may act as a negative regulator, in some immunological contexts, for antibody production in the mammalian host.

Relationship between surface accessibility for PpmA, PsaA, and PspA and antibody-mediated immunity to systemic infection by Streptococcus pneumoniae

Antibodies to capsular polysaccharide (PS) are protective against systemic infection by Streptococcus pneumoniae, but the large number of pneumococcal serogroups and the age-related immunogenicity of pure PS limit the utility of PS-based vaccines. In contrast, cell wall-associated proteins from different capsular serotypes can be cross-reactive and immunogenic in all age groups. Therefore, we evaluated three pneumococcal proteins with respect to relative accessibility to antibody, in the context of intact pneumococci, and their ability to elicit protection against systemic infection by encapsulated S. pneumoniae. Sequences encoding pneumococcal surface adhesin A (PsaA), putative protease maturation protein A (PpmA), and the N-terminal region of pneumococcal surface protein A (PspA) from S. pneumoniae strain A66.1 were cloned and expressed in Escherichia coli. The presence of genes encoding PsaA, PpmA, and PspA in 11 clinical isolates was examined by PCR, and the expression of these proteins by each strain was examined by Western blotting with antisera raised to the respective recombinant proteins. We used flow cytometry to demonstrate that PspA was readily detectable on the surface of the pneumococcal strains analyzed, whereas PsaA and PpmA were not. Consistent with these observations, mice with passively or actively acquired antibodies to PspA or type 3 PS were equivalently protected from homologous systemic challenge with type 3 pneumococci, whereas mice with passively or actively acquired antibodies to PsaA or PpmA were not effectively protected. These experiments support the hypothesis that the extent of protection against systemic pneumococcal infection is influenced by target antigen accessibility to circulating host antibodies.

Alloreactivity in Renal Transplant Recipients with and without Chronic Allograft Nephropathy

The pathogenesis of chronic allograft nephropathy (CAN) involves both immunologic (antigen-dependent) and nonimmunologic (antigen-independent) mechanisms. In order to provide further insight into the immunologic basis of this disease, a cross-sectional analysis of cellular and humoral immunity in human renal allograft recipients with or without deteriorating renal function and biopsy proven CAN was performed. Interferon-gamma enzyme-linked immunosorbent spot assays were used to assess cellular immunity to donor, or fully mismatched third-party stimulator cells (direct pathway), and to synthetic peptides derived from donor HLA molecules (indirect pathway). Anti-HLA antibodies were evaluated by flow cytometry using HLA-coated beads. Both the mean frequencies of donor-reactive peripheral blood lymphocytes and the number of individuals who responded to donor antigens per group were statistically higher in CAN patients versus control subjects (P < 0.02). Calculated ratios of donor/third-party enzyme-linked immunosorbent spot responses showed mean values of 2.61 +/- 3.0 in the CAN group, with ratios of 0.50 to 0.72 +/- 0.42 in control subjects (P < 0.001), confirming that direct, donor-specific cellular immunity predominated in patients with CAN. Fifty percent of CAN patients studied exhibited donor peptide reactivity compared with only 28.6% in control subjects. Finally, 33% of patients in the CAN group developed new posttransplantation anti-HLA antibodies compared with only 4% in the control group (P < 0.05). Overall, the results suggest that persistent cell-mediated and humoral alloimmunity contribute to the development of CAN and further demonstrate that anti-donor immunity in patients with CAN is heterogeneous. Immune monitoring to predict long-term outcome should include multiple measures of cellular and humoral immunity.

Genetic variation influences the B-cell response to immunization with a pneumococcal polysaccharide conjugate vaccine

CBA/J mice immunized with pneumococcal 23F-CRM(197) vaccine produce significantly lower titers of 23F-specific antibodies and fewer 23F-specific antibody-secreting cells (ASC) than did BALB/c or (CBA/J x BALB/c)F(1) (CCBAF(1)) mice. The reduced 23F-specific titers of CBA/J versus BALB/c or CCBAF(1) mice are presumably related to lower frequencies of 23F-specific ASC influenced by genetic variation.

Mapping the antigenicity of copper-treated cellular prion protein with the scrapie isoform

When recombinant and cellular prion protein (PrP(C)) binds copper, it acquires properties resembling the scrapie isoform (PrP(Sc)), namely protease resistance, detergent insolubility and increased beta sheet content. However, whether the conformations of PrP(C) induced by copper and PrP(Sc) are similar has not been studied in great detail. Here, we use a panel of seven monoclonal antibodies to decipher the epitopes on full-length mouse PrP(C) that are affected by exogenous copper, and to compare the antigenicity of the copper-treated full-length PrP(C) with the full-length PrP(Sc) present in scrapie-infected mouse brains. In the presence of copper, we found that epitopes along residues 115-130 and 153-165 become more accessible on PrP(C). These regions correspond to the two beta sheet strands in recombinant PrP and they were proposed to be important for prion conversion. However, when we compared the antibody-binding patterns between full-length PrP(C) with full-length PrP(Sc) and between copper-treated full-length PrP(C) with full-length PrP(Sc), antibody binding to residues 143-155 and 175-185 was consistently increased on PrP(Sc). Collectively, our results suggest that copper-treated full-length PrP(C) does not resemble full-length PrP(Sc), despite acquiring PrP(Sc)-like properties. In addition, since each full-length protein reacts distinctively to some of the antibodies, this binding pattern could discriminate between PrP(C) and PrP(Sc).

Significant variation in serotype-specific immunogenicity of the seven-valent Streptococcus pneumoniae capsular polysaccharide-CRM197 conjugate vaccine occurs despite vigorous T cell help induced by the carrier protein

Streptococcus pneumoniae capsular polysaccharides (PnPSs) induce protective antibodies but are T cell-independent type 2 antigens and are poorly immunogenic in infants. Conjugate vaccines of PnPSs linked to proteins like cross-reactive material (CRM(197)) increase PS antibody titer and elicit immunologic memory in infants. Despite being linked to an identical carrier protein, each PS component of the 7-valent PnPS-CRM(197) vaccine has different immunogenicity. To determine whether variations in conjugate-induced memory T cell responses or PnPS-specific antibody-secreting cells (ASCs) were responsible for serotype-specific differences in immunogenicity, adults were immunized with 7-valent PnPS-CRM(197), and antibody titer, vaccine component-specific CD4(+) T cell recall response, numbers of PnPS-specific ASCs, and cytokine production were measured. PnPS-CRM(197) induced significantly different serotype-specific antibody titers, despite vigorous T cell recall responses to all 7 vaccine components, and production of interleukin (IL)-2, IL-5, IL-6, IL-10, and interferon-gamma. We conclude that PnPS-CRM(197) induces variable serotype-specific antibody titers, despite induction of comparable CRM(197)-specific memory T cell responses.

Enhanced immunogenicity of pneumococcal surface adhesin A by genetic fusion to cytokines and evaluation of protective immunity in mice

Immunization of mice with pneumococcal surface adhesin A (PsaA) emulsified in complete Freund's adjuvant (CFA) provides protection against systemic infection with Streptococcus pneumoniae. Because the use of CFA is not acceptable in humans, we sought to develop alternative means of enhancing the immunogenicity of protein antigens of potential use in pneumococcal vaccines. We designed a series of genetic constructs in which coding sequences for PsaA were linked to sequences encoding either murine interleukin-2 (mIL-2), mIL-4, or two copies of an immunostimulatory nonapeptide derived from mIL-1beta. The PsaA-cytokine constructs were cloned and expressed in Escherichia coli. Mice immunized twice with PsaA-IL-2, or PsaA-IL-4 responded with PsaA-specific antibody production comparable in magnitude to that of mice primed with PsaA in CFA and boosted with PsaA in incomplete Freund's adjuvant (PsaA-Adj). Antibodies elicited by PsaA-Adj were predominantly of the immunoglobulin G1 (IgG1) subclass, while PsaA-IL-2 and PsaA-IL-4 elicited substantial amounts of IgG2a in addition to IgG1. Mice immunized with PsaA-Adj or PsaA-IL-4 were partially protected against intraperitoneal challenge with virulent S. pneumoniae (30% overall survival beyond 15 days postchallenge). Mice immunized with PsaA and no adjuvant or PsaA-IL-2 exhibited 0 or 5% survival rates, respectively, following challenge. In contrast, mice immunized twice with capsular polysaccharide were 100% protected. The modest levels of protection seen in mice immunized with PsaA and its more immunogenic derivatives may be explained in part by the relative inaccessibility of antibody to PsaA on the surface of encapsulated S. pneumoniae.

Evolution of the enzyme-linked immunosorbent spot assay for post-transplant alloreactivity as a potentially useful immune monitoring tool

Post-transplant monitoring of cellular immunity has the potential to guide alterations in medical therapy. To this end, our laboratory has developed an enzyme-linked immunosorbent spot (ELISPOT) assay for detection of peripheral blood alloimmunity. Peripheral blood lymphocytes (PBLs) from normal volunteers and from renal allograft recipients were tested against donor stimulator cells for their ability to respond in 'one-way' cytokine ELISPOT assays. T cell depletion of donor spleen or PBLs eliminated donor cell cytokine secretion while preserving the ability of these cells to present allo-antigen to responding T cells. Alloreactive IFN-gamma-producing PBLs derive from the memory T cell pool and are readily detectable in recipients of renal allografts taking immunosuppressant medications. A significant expansion of IFN-gamma-producing donor-reactive memory PBLs was detectable at 4-6 months post-transplant in those who had experienced an acute rejection episode compared with those with a stable post-transplant course. The data demonstrate the feasibility of repeated post-transplant monitoring of allograft recipients, and provide the foundation for improving the care of human transplant recipients through rational clinical decision-making based on measures of immune function.

Gamma 3 gene-disrupted mice selectively deficient in the dominant IgG subclass made to bacterial polysaccharides. II. Increased susceptibility to fatal pneumococcal sepsis due to absence of anti-polysaccharide IgG3 is corrected by induction of anti-polysaccharide IgG1

Bacterial polysaccharides (PS) are type 2 T-independent Ags that elicit Abs restricted in isotype to IgM and predominantly IgG2 in humans and IgM, and IgG3 in mice. Humans with IgG2 subclass deficiency are susceptible to sinus and pulmonary infections with PS-encapsulated bacteria. We previously developed an IgG3-deficient mouse by disrupting the gamma3 H chain constant region gene via targeted mutagenesis. Mutant mice lacking IgG3 were backcrossed for 10 generations to wild-type (WT) BALB/c mice to generate BALB/c mice that have complete absence of IgG3. WT mice immunized with type 3 Streptococcus pneumoniae capsular PS made anti-PS IgM, IgG3, and small quantities of IgG1, which opsonized S. pneumoniae for killing by polymorphonuclear leukocytes. These mice were protected against death from lethal doses of type 3 S. pneumoniae. In contrast, IgG3(-/-) mice made similar titers of anti-PS IgM and IgG1 as WT mice but no IgG3, and had poorly opsonic sera with significantly increased mortality after S. pneumoniae challenge. Immunization of IgG3(-/-) mice with type 3 S. pneumoniae PS conjugated to carrier protein CRM(197)-elicited IgM and high-titer IgG1 Abs, restored serum opsonization, and gave protection from mortality after S. pneumoniae, challenge comparable to WT mice. We conclude that mice lacking the dominant IgG3 subclass made to bacterial PS are more susceptible to fatal S. pneumoniae sepsis than WT mice, but that IgG1 induced by a S. pneumoniae glycoconjugate can adequately protect against S. pneumoniae sepsis. This model suggests that IgG subclass of anti-PS Ab is an important component of immunity to encapsulated bacteria.

Immunization with Haemophilus influenzae type b-CRM(197) conjugate vaccine elicits a mixed Th1 and Th2 CD(4+) T cell cytokine response that correlates with the isotype of antipolysaccharide antibody

Haemophilus influenzae type b (Hib) capsular polysaccharide (PS) induces protective antibodies but is T independent and poorly immunogenic in infants. Conjugate vaccines of Hib PS linked to proteins, such as CRM(197), increase the PS antibody titer and elicit immunologic memory. To define the conjugate-induced memory T cell response, 19 adults were immunized with Hib-CRM(197), and antibody titers, carrier protein-specific CD4(+) T cell proliferation, and cytokine production were measured. Hib-CRM(197) induced PS and CRM(197) antibodies, vigorous T cell recall responses, and production of cytokines, including interleukin (IL)-2, IL-5, IL-10, and interferon-gamma. There was marked variability in PS antibody titer, despite consistent CRM(197)-specific recall responsiveness, which correlated with peak IgM and IgA PS antibody titers. Correlations were also found between IL-2 and IL-5 and IgA PS antibody levels. Hib-CRM(197) induced a rapid increase in CRM(197)-specific memory T cells and mixed Th1/Th2 cytokines, which may regulate the isotype and quantity of PS antibody.