T-Cell epitopes and human leukocyte antigen restriction elements of an immunodominant antigen of Blastomyces dermatitidis

Generation and expression analysis of BAC humanized mice carrying HLA-DP401 haplotype

Background

Human leukocyte antigen (HLA)-DP is much less studied than other HLA class II antigens, that is, HLA-DR and HLA-DQ, etc. However, the accumulating data have suggested the important roles of DP-restricted responses in the context of cancer, allergy, and infectious disease. Lack of animal models expressing these genes as authentic cis-haplotypes blocks our understanding for the role of HLA-DP haplotypes in immunity.

Methods

To explore the potential cis-acting control elements involved in the transcriptional regulation of the HLA-DPA1/DPB1 gene, we performed the expression analysis using bacterial artificial chromosome (BAC)-based transgenic humanized mice in the C57BL/6 background, which carried the entire HLA-DP401 gene locus. We further developed a mouse model of Staphylococcus aureus pneumonia in HLA-DP401 humanized transgenic mice, and performed the analysis on the expression pattern of HLA-DP401 and immunological responses in the model.

Results

In this study, we screened and identified a BAC clone spanning the entire HLA-DP gene locus. DNA from this clone was analyzed for integrity by pulsed-field gel electrophoresis and then microinjected into fertilized mouse oocytes to produce transgenic founder animals. Nine sets of PCR primers for regional markers with an average distance of 15 kb between each primer were used to confirm the integrity of the transgene in the five transgenic lines carrying the HLA-DPA1/DPB1 gene. Transgene copy numbers were determined by real-time PCR analysis. HLA-DP401 gene expression was analyzed at the mRNA and protein level. Although infection with S aureus Newman did not alter the percentage of immune cells in the spleen and thymus from the HLA-DP401-H2-Aβ1 humanized mice. Increased expression of HLA-DP401 was observed in the thymus of the humanized mice infected by S aureus.

Conclusions

We generated several BAC transgenic mice, and analyzed the expression of HLA-DPA1/DPB1 in those mice. A model of Saureus-induced pneumonia in the HLA-DP401-H2-Aβ1-/- humanized mice was further developed, and S aureus infection upregulated the HLA-DP401 expression in thymus of those humanized mice. These findings demonstrate the potential of those HLA-DPA1/DPB1 transgenic humanized mice for developing animal models of infectious diseases and MHC-associated immunological diseases.

The Role of the Interleukin-17 Axis and Neutrophils in the Pathogenesis of Endemic and Systemic Mycoses

Systemic and endemic mycoses are considered life-threatening respiratory diseases which are caused by a group of dimorphic fungal pathogens belonging to the genera Histoplasma, Coccidioides, Blastomyces, Paracoccidioides, Talaromyces, and the newly described pathogen Emergomyces. T-cell mediated immunity, mainly T helper (Th)1 and Th17 responses, are essential for protection against these dimorphic fungi; thus, IL-17 production is associated with neutrophil and macrophage recruitment at the site of infection accompanied by chemokines and proinflammatory cytokines production, a mechanism that is mediated by some pattern recognition receptors (PRRs), including Dectin-1, Dectine-2, TLRs, Mannose receptor (MR), Galectin-3 and NLPR3, and the adaptor molecules caspase adaptor recruitment domain family member 9 (Card9), and myeloid differentiation factor 88 (MyD88). However, these PRRs play distinctly different roles for each pathogen. Furthermore, neutrophils have been confirmed as a source of IL-17, and different neutrophil subsets and neutrophil extracellular traps (NETs) have also been described as participating in the inflammatory process in these fungal infections. However, both the Th17/IL-17 axis and neutrophils appear to play different roles, being beneficial mediating fungal controls or detrimental promoting disease pathologies depending on the fungal agent. This review will focus on highlighting the role of the IL-17 axis and neutrophils in the main endemic and systemic mycoses: histoplasmosis, coccidioidomycosis, blastomycosis, and paracoccidioidomycosis.

Role of HLA-DP in the Presentation of Epitopes from the Truncated Bacterial PE38 Immunotoxin

Identification of helper T-cell epitopes is important in many fields of medicine. We previously used an experimental approach to identify T-cell epitopes in PE38, a truncated bacterial toxin used in immunotoxins. Here, we evaluated the ability of antibodies to DR, DP, or DQ to block T-cell responses to PE38 epitopes in 36 PBMC samples. We predicted the binding affinities of peptides to DR, DP, and DQ alleles using computational tools and analyzed their ability to predict the T-cell epitopes. We found that HLA-DR is responsible for 65% of the responses, DP 24%, and DQ 4%. One epitope that is presented in 20% of the samples (10/50) is entirely DP restricted and was not predicted to bind to DR or DP reference alleles using binding algorithms. We conclude that DP has an important role in helper T-cell response to PE38.

Blastomyces gilchristii as Cause of Fatal Acute Respiratory Distress Syndrome

Since the 2013 description of Blastomyces gilchristii, research describing the virulence or clinical outcome of B. gilchristii infection has been lacking. We report molecular evidence of B. gilchristii as an etiologic agent of fatal acute respiratory distress syndrome. B. gilchristii infection was confirmed by PCR and sequence analysis.

Common and emerging fungal pulmonary infections

Fungal pulmonary infections are becoming more prevalent as a consequence of the rising prevalence of immunocompromised patients. Besides ubiquitous opportunistic fungi such as Aspergillus spp and geographically delimited mycoses, fungi that were previously thought to be of uncertain pathogenicity, such as hyaline and dematiaceous molds, are increasingly being diagnosed as the causes of invasive disease in profoundly immunosuppressed hosts. Overall progress in the clinical management of fungal pulmonary infections has been slow compared with other areas of infectious diseases. However, recent encouraging advances in fungal diagnostics and therapeutics have resulted in improved clinical outcomes, particularly in vulnerable patient populations such as solid organ or allogeneic hematopoietic stem cell transplant recipients. This article provides an overview of endemic mycoses and other emerging fungal pulmonary infections. Recent developments in terms of the diagnosis and clinical management of these infections are also discussed.

Blastomycosis: new insights into diagnosis, prevention, and treatment

The basic science and clinical understanding of infection with Blastomyces dermatitidis has been a field of constant evolution and continued revision of hypotheses. This article highlights some areas in which recent progress has the potential for significant impact on the clinical care of patients. Specifically, this article examines the application of modern technology to epidemiologic studies, the development of novel vaccine candidates, emerging populations at risk for the disease, rapid diagnostic tools, and the application of novel antifungal agents in the treatment of blastomycosis.

Progress in vaccination for histoplasmosis and blastomycosis: coping with cellular immunity

Human infection with Histoplasma capsulatum or Blastomyces dermatitidis is sufficiently frequent to warrant exploring the development of vaccines. This review examines the advancements that have been accomplished over the last few years. The availability of molecular tools to create recombinant antigens or mutant strains has produced a small number of useful vaccine candidates. More importantly, the studies summarized herein demonstrate that understanding the host response to a protein or mutant fungus is critical to creating a vaccine that may be useful for the immunocompromised patient.

HLA-DP4 presents an immunodominant peptide from the RSV G protein to CD4 T cells

CD4 T cells play a crucial role during virus infections by producing antiviral cytokines and by regulating humoral and cellular immune responses. Unfortunately however, exaggerated CD4 T cell responses can cause significant immune-mediated disease as was observed during RSV infections in children previously vaccinated with a formalin-inactivated virus in the 1960s. It has been observed that vaccination with the G protein of RSV tends to prime mice for a similar Th2-mediated enhanced disease. Whether the G protein may play a role in enhanced disease in man is unclear. In the present study, we identified an immunodominant epitope in the conserved region of the G protein encompassing amino acid residues 162-175. This epitope is presented in the context of HLA-DPB1*0401 and DPB1*0402, the most prevalent HLA class II alleles. Importantly, in some patients, a mixed Th1/Th2 response against this epitope was found in bronchoalveolar lavage samples during primary RSV infections.

Identification of novel immunodominant CD4+ Th1-type T-cell peptide epitopes from herpes simplex virus glycoprotein D that confer protective immunity

The molecular characterization of the epitope repertoire on herpes simplex virus (HSV) antigens would greatly expand our knowledge of HSV immunity and improve immune interventions against herpesvirus infections. HSV glycoprotein D (gD) is an immunodominant viral coat protein and is considered an excellent vaccine candidate antigen. By using the TEPITOPE prediction algorithm, we have identified and characterized a total of 12 regions within the HSV type 1 (HSV-1) gD bearing potential CD4(+) T-cell epitopes, each 27 to 34 amino acids in length. Immunogenicity studies of the corresponding medium-sized peptides confirmed all previously known gD epitopes and additionally revealed four new immunodominant regions (gD(49-82), gD(146-179), gD(228-257), and gD(332-358)), each containing naturally processed epitopes. These epitopes elicited potent T-cell responses in mice of diverse major histocompatibility complex backgrounds. Each of the four new immunodominant peptide epitopes generated strong CD4(+) Th1 T cells that were biologically active against HSV-1-infected bone marrow-derived dendritic cells. Importantly, immunization of H-2(d) mice with the four newly identified CD4(+) Th1 peptide epitopes but not with four CD4(+) Th2 peptide epitopes induced a robust protective immunity against lethal ocular HSV-1 challenge. These peptide epitopes may prove to be important components of an effective immunoprophylactic strategy against herpes.

Mutation of the WI-1 gene yields an attenuated blastomyces dermatitidis strain that induces host resistance

Systemic fungal infections are becoming more common and difficult to treat, and vaccine prevention is not available. Pulmonary infection with the dimorphic fungus Blastomyces dermatitidis often progresses and requires treatment to prevent fatality. We recently created a recombinant strain of the fungus lacking the WI-1 adhesin and pathogenicity. We show here that administration of viable yeast of this attenuated strain vaccinates against lethal pulmonary experimental infection due to isogenic and nonisogenic strains from diverse geographic regions. To our knowledge, this is the first example of a recombinant attenuated vaccine against fungi. The vaccine induces delayed-type hypersensitivity and polarized type 1 cytokine responses, which are linked with resistance. A cell-wall/membrane (CW/M) antigen from the vaccine strain also induces polarized and protective immune responses. Lymph node cells and CD4(+) T-cell lines raised with CW/M antigen transfer protective immunity when they release type 1 cytokine IFN-gamma, but not when they release IL-4, and neutralization of IFN-gamma confirmed its role in vivo. Thus, by mutating a pathogenetic locus in a dimorphic fungus, we have created an attenuated vaccine strain and have begun to elucidate fungal and host elements requisite for vaccine immunity.

Cell wall biogenesis of Blastomyces dermatitidis. Evidence for a novel mechanism of cell surface localization of a virulence-associated adhesin via extracellular release and reassociation with cell wall chitin

Pathogenic yeast of Blastomyces dermatitidis express a surface protein adhesin, WI-1. Due to the crucial role of WI-1 in adherence and disease pathogenesis, we investigated how the protein localizes to the surface of B. dermatitidis. WI-1 released extracellularly by wild-type yeast coated the surfaces of co-cultured knockout yeast within 3 h of incubation, implying that secreted WI-1 provides a pathway for loading the protein onto the yeast cell wall. In radioligand binding assays, purified WI-1 bound saturably, specifically, and with high affinity (K(d) = 8.3 x 10(-9)) to the cell surface of knockout yeast devoid of WI-1. WI-1 added exogenously, in vitro, to knockout yeast was indistinguishable from native cell surface WI-1 by fluorescence staining and restored adhesivity to the knockout yeast in macrophage binding and phagocytosis assays. Analysis of interactions between WI-1 and elements of the yeast cell wall identified chitin as the anchor point for WI-1. This interaction was shown to hinge on the 24-amino acid tandem repeat sequence of WI-1. Efforts to extract surface WI-1 from the yeast demonstrated that it is fastened to the wall by non-covalent interactions and covalent links between cysteine residues. We conclude that the yeast cell surface adhesin WI-1 localizes to the cell wall, in part, through extracellular release followed by high affinity binding back onto exposed chitin fibrils. These findings point to a novel pathway of cell wall biogenesis in yeast and an unanticipated role for chitin in anchoring and displaying a surface adhesin and virulence determinant.