African strains of Blastomyces dermatitidis that do not express surface adhesin WI-1.

African strains of Blastomyces dermatitidis differ from North American strains in their growth, morphology, and clinical disease phenotype. In addition, two serotypes, designated 1 and 2, have been described. We investigated African strains of B. dermatitidis for expression of the surface protein adhesin WI-1 and found that serotype 2 strains do not express it because they lack the coding sequence in their genome. The defect will make the strains useful for gene complementation and for testing the pathogenetic role of the WI-1 adhesin.     

Purification and characterization of the major antigen WI-1 from Blastomyces dermatitidis yeasts and immunological comparison with A antigen.

The lack of well-defined antigens from Blastomyces dermatitidis has hampered the ability to reliably diagnose human infection and study the immunobiology of blastomycosis. We recently discovered a novel surface protein on B. dermatitidis yeasts, designated WI-1, and demonstrated it to be a key antigenic target of humoral and cellular responses during infection. In the present article, we purified and characterized WI-1 and compared it immunologically with the only Blastomyces antigen commercially available, A antigen. WI-1 was purified by high-performance liquid chromatography over a DEAE-cellulose column. It eluted from the column at a point on the salt gradient corresponding to 460 to 490 mM NaCl, reflecting its acidic pI of approximately equal to 5.2. Purified WI-1 had a molecular mass of 120 kDa and contained a large amount of cysteine (85 residues) and aromatic amino acids but undetectable carbohydrate. In contrast, A antigen had a molecular mass of 135 kDa and contained 37% carbohydrate. Immunological comparison of the two antigens showed that, when radiolabeled, WI-1 was more reactive with anti-Blastomyces antisera than A antigen but did not cross-react with anti-Histoplasma antisera. Proteinase digestion of WI-1 eliminated its recognition by anti-WI-1 and anti-Blastomyces antisera. Proteinase treatment of A antigen had no effect on its recognition by anti-Blastomyces or anti-Histoplasma antisera, but periodate treatment abolished recognition by anti-Histoplasma antisera, indicating that the cross-reactive determinant(s) of A antigen is displayed on the accompanying carbohydrate. In further studies, anti-WI-1 antiserum reacted with A antigen and, conversely, anti-A antiserum and monoclonal antibodies (MAbs) reacted with WI-1, indicating a shared determinant on the two antigens. A recombinant 25-amino-acid repeat, recently cloned from WI-1 and found to be the major target of antibody recognition of WI-1, reacted strongly with anti-A antiserum and MAbs. In MAb competition tests, MAbs specific for the 25-residue repeat abolished binding of anti-A antiserum to A antigen. In antigen inhibition tests, the recombinant repeat abolished binding of anti-A antiserum to A antigen. These results demonstrate that the repeat is the major site of antibody recognition of both WI-1 and A antigen and that the recombinant, nonglycosylated peptide could replace either native antigen in formatting better diagnostic tests for blastomycosis. Moreover, they suggest that producing fungal protein antigens as nonglycosylated peptides in a procaryotic expression system may circumvent problems of antigen cross-reactivity that are due to posttranslational modification.     

Altered expression of surface protein WI-1 in genetically related strains of Blastomyces dermatitidis that differ in virulence regulates recognition of yeasts by human macrophages.

The molecular basis for pathogenicity and virulence of the dimorphic fungus Blastomyces dermatitidis remains unknown. WI-1 is a major cell wall protein of B. dermatitidis yeasts and is a recognition target of both humoral and cell-mediated immunity. As an initial study to determine if WI-1 might be linked to virulence of B. dermatitidis, we quantified WI-1 expression on three genetically related strains that differ in their virulence for mice: wild-type virulent ATCC strain 26199, mutant ATCC strain 60915 (which is 10,000-fold reduced in virulence), and mutant ATCC strain 60916 (which is avirulent). Two principal alterations in WI-1 expression were observed in the mutants. First, the mutants express more WI-1 on their surface, as quantified by flow cytometry with monoclonal antibody to WI-1 and by radioimmunoassay, but the WI-1 on their cell wall is less extractable than that on the wild-type strain. Second, the mutants shed less WI-1 during culture and demonstrate impaired processing of shed WI-1. Surface alterations in WI-1 were accompanied by significant differences in the binding of the virulent and mutant strains to human monocyte-derived macrophages. Attachment of yeasts to macrophages paralleled and was proportional to the expression of WI-1. Compared with wild-type yeasts, both mutants bound to macrophages more rapidly and in two- to threefold-greater magnitude. Furthermore, about 75% of yeast binding to macrophages was inhibited by a Fab anti-WI-1 monoclonal antibody. These results suggest that altered WI-1 expression on attenuated and avirulent mutant B. dermatitidis yeasts greatly facilitates macrophage recognition and binding of yeasts and, in turn, may contribute to more rapid ingestion and killing in the host.     

In vivo and in vitro cell-mediated immune responses to a cell wall antigen of Blastomyces dermatitidis.

An alkali-soluble, water-soluble cell wall fraction of Blastomyces dermatitidis, designated B-ASWS, was evaluated as an antigen for detecting in vivo (skin tests) and in vitro migration inhibition factor (MIF) production and lymphocyte transformation (LT) responses in Blastomyces-infected guinea pigs. The biological activity of B-ASWS was compared with that of blastomycin KCB-26. The superiority of B-ASWS, in terms of its sensitivity and specificity, was evident in in vivo and in vitro assays. Skin tests responses were obtained in 21 of the 24 Blastomyces-infected guinea pigs, whereas only one of the 14 Histoplasma-infected guinea pigs were significantly greater than those obtained using cell populations from Histoplasma-infected or noninfected guinea pigs. The con-MIF and LT in peritoneal exudate cells and lymph node cells of homologuosly infected animals. In each biological system, the response of the Blastomyces-infected guinea pigs were significantly greater than those obtained using cell populations from Histoplasma-infected or non-infected guinea pigs. The contrasting efficacy of B-ASWS as compared with blastomycin KCB-26, suggests that the cell wall antigen will be a useful tool for detecting cell-mediated immune responses in blastomycosis.     

Identification and characterization of epitopes on the 120-kilodalton surface protein antigen of Rickettsia prowazekii with synthetic peptides.

The 120-kDa surface protein antigens (SPAs) of typhus rickettsiae are highly immunogenic and have been shown to be responsible for the species-specific serological reactions of the typhus group rickettsiae. To study the immunochemistry of these proteins, overlapping decapeptides encompassing the whole protein were synthesized on derivatized polyethylene pins. A modified enzyme-linked immunosorbent assay was used to identify epitopes recognized by rabbit hyperimmune antisera to Rickettsia prowazekii SPA. Eight distinct epitopes were mapped by this method in three regions. Four of the epitopes, which were located in the carboxyterminus of mature processed SPA, were strongly competitively inhibited by native folded SPA but not by intact rickettsiae, suggesting that they were on the SPA surface but not exposed on the rickettsial surface. Three of these epitopes were present on both R. prowazekii and Rickettsia typhi SPAs. The immunoreactivities of five epitopes were further characterized by synthesizing modified peptides. Glycine substitution experiments determined the critical residues in the epitopes. The dependence of binding of the peptide epitopes to the polyclonal antisera was mapped to single residues. The limited number and weak reactivity of linear peptide epitopes observed with human and rabbit sera, possibly due to a lack of the methylated amino acids which are present in rickettsia-derived SPA, suggest that the present approach will not provide useful synthetic antigens for diagnosis of typhus infections.     

A 35-kilodalton protein is a major target of the human immune response to Mycobacterium leprae.

The control of leprosy will be facilitated by the identification of major Mycobacterium leprae-specific antigens which mirror the immune response to the organism across the leprosy spectrum. We have investigated the host response to a 35-kDa protein of M. leprae. Recombinant 35-kDa protein purified from Mycobacterium smegmatis resembled the native antigen in the formation of multimeric complexes and binding by monoclonal antibodies and sera from leprosy patients. These properties were not shared by two forms of 35-kDa protein purified from Escherichia coli. The M. smegmatis-derived 35-kDa protein stimulated a gamma interferon-secreting T-cell proliferative response in the majority of paucibacillary leprosy patients and healthy contacts of leprosy patients tested. Cellular responses to the protein in patients with multibacillary leprosy were weak or absent, consistent with hyporesponsiveness to M. leprae characteristic of this form of the disease. Almost all leprosy patients and contacts recognized the 35-kDa protein by either a T-cell proliferative or an immunoglobulin G antibody response, whereas few tuberculosis patients recognized the antigen. This specificity was confirmed in guinea pigs, with the 35-kDa protein eliciting strong delayed-type hypersensitivity in M. leprae-sensitized animals but not in those sensitized with Mycobacterium tuberculosis or Mycobacterium bovis BCG. Therefore, the M. leprae 35-kDa protein appears to be a major and relatively specific target of the human immune response to M. leprae and is a potential component of a diagnostic test to detect exposure to leprosy or a vaccine to combat the disease.     

The effect of canine macrophages on the adherence and growth of Blastomyces dermatitidis yeast: evidence of a soluble factor that enhances the growth of B. dermatitidis yeast

Blastomycosis is a medically important systemic fungal infection of dogs and humans. Phagocytic cells are the first line of cellular defence against B. dermatitidis, and are a prominent feature in the lesions and exudate of canine blastomycosis. The adherence of B. dermatitidis yeast to canine phagocytes, and the effects of such adherence on the growth of B. dermatitidis yeast, has not been previously reported. The results of this study demonstrate that canine complement enhances the adherence of B. dermatitidis yeast to canine macrophages. Initiation of the canine complement cascade by B. dermatitidis yeast appeared to occur predominantly by the classical pathway. Adherence of B. dermatitidis yeast to canine macrophages enhanced the growth of the yeast. In the absence of macrophages, this effect could be duplicated by incubating yeast in conditioned medium from co-cultures of macrophages and yeast. This observation suggests that a soluble factor is involved in the growth enhancement of the yeast, These findings provide new insights into the adherence of B. dermatitidis yeast to canine macrophages, and how adherence influences the proliferation of B. dermatitidis yeast.     

Interleukin 12 as an adjuvant to WI-1 adhesin immunization augments delayed-type hypersensitivity, shifts the subclass distribution of immunoglobulin G antibodies, and enhances protective immunity to Blastomyces dermatitidis infection

Cell-mediated immunity is pivotal in host resistance to Blastomyces dermatitidis infection. Immunization of mice with the WI-1 adhesin enhances resistance against experimental pulmonary infection but elicits features of a mixed T-helper-cell immune response. Immune mice acquire delayed-type hypersensitivity (DTH) but also high titers of WI-1-specific immunoglobulin G1 (IgG1) and IgG2b, a result indicative of T-helper-2 cellular immunity. We report that interleukin-12, used as an adjuvant for WI-1 immunization, augments DTH, shifts the balance of the T-helper phenotype toward Th1, and enhances resistance to B. dermatitidis infection.     

Identification of the active precipitin components in a purified preparation of the A antigen of Blastomyces dermatitidis.

A purified A-antigen preparation of Blastomyces dermatitidis was determined to be composed of five major glycoprotein bands, visible with Coomassie blue and periodic acid-Schiff staining of polyacrylamide gels. At least 20 additional protein bands were detected by using a silver stain, which was 100 times more sensitive than the Coomassie method. Two components of this mixture were determined to be associated with the A-antigenic activity of B. dermatitidis. Of several antigen preparations examined in Ouchterlony precipitation tests, those reactive with a reference anti-A antiserum contained the slowest moving of the Coomassie blue bands. The antigen preparations without precipitin reactivity lacked this protein band. Two protein bands were shown to disappear from an antigen preparation after incubation with an affinity gel linked to the reference anti-A serum. One of the bands was the slowest Coomassie blue band, and the other was a fast-migrating protein detectable only with the silver stain. Characterization of the components responsible for the A-antigenic activity has important applications in the production and standardization of serological reagents for the diagnosis of blastomycosis.     

Extracellular calcium and magnesium, but not iron, are needed for optimal growth of Blastomyces dermatitidis yeast form cells in vitro

In the present study, we demonstrate that the yeast form of Blastomyces dermatitidis can proliferate for short periods of time in the absence of ferric iron but not in the absence of calcium or magnesium. The results of this study shed light on the resistance of B. dermatitidis to chelating agents, such as deferoxamine, and may explain how B. dermatitidis resists the iron-binding activity of serum transferrin.     

Opposite effects of human monocytes, macrophages, and polymorphonuclear neutrophils on replication of Blastomyces dermatitidis in vitro.

The purpose of this study was to determine the effects of human monocytes, macrophages, and polymorphonuclear neutrophils (PMN) on the fungal pathogen Blastomyces dermatitidis in vitro. Peripheral blood monocyte monolayers significantly inhibited the replication of a virulent strain (V) and an avirulent strain (AV) of B. dermatitidis by 35 and 28%, respectively. Macrophage monolayers, derived from monocytes by in vitro culturing for 9 days, also inhibited the replication of V and AV in 24-h cocultures; in 72-h cocultures, the inhibition was increased (85 and 88%, respectively). By contrast, PMN stimulated the replication of V and AV in 24-h cocultures (i.e., 45%; AV, 18%) and in 72-h cocultures (V, 68%; AV, 65%). No effect was observed in 2-h cocultures of PMN and B. dermatitidis, even though Candida albicans was killed by PMN in concurrent experiments. PMN stimulated replication of V in a dose-dependent manner, and viability of PMN was not a requirement for the achievement of this effect. These results indicate that monocytes and macrophages significantly inhibited the replication of B. dermatitidis, whereas PMN had an opposite effect. Our findings raise the possibility that these phagocytic cells may have similar opposing effects on the replication of B. dermatitidis in vivo.     

The recombinant 120-kilodalton protein of Ehrlichia chaffeensis, a potential diagnostic tool.

DNA encoding two repeat units of 120-kDa protein of Ehrlichia chaffeensis was cloned into the expression vector pGEX and expressed in Escherichia coli. The sensitivity and specificity of a dot blot assay for detection of human antibodies with the recombinant protein were 86 and 100%, respectively, compared with an indirect immunofluorescence assay.     

Composition, serologic reactivity, and immunolocalization of a 120-kilodalton tube precipitin antigen of Coccidioides immitis.

Diagnosis of coccidioidomycosis largely depends on serologic tests. In this investigation, the enzyme-linked immunosorbent assay (ELISA) was used to detect patient immunoglobulin M (IgM) precipitin antibody binding to a 120-kilodalton (kDa) fraction previously isolated from an alkali-soluble, water-soluble extract of the arthroconidial wall and mycelial culture filtrate plus toluene lysate of Coccidioides immitis. Results of the serologic response to this tube precipitin antigen (TP-Ag) in the ELISA correlated well with results of immunodiffusion assays of 30 serum samples from patients. Immunoelectron microscopic examinations of arthroconidia and spherules were performed with patient IgM precipitin antibodies isolated from sera eluted over a solid-phase immunosorbent column containing the purified 120-kDa TP-Ag. The antibody probe located the 120-kDa TP-Ag on the walls of in vitro-grown arthroconidia and spherules. Pronase digestion and heating (100 degrees C, 5 min) had no apparent effect on the activity of the 120-kDa TP-Ag, while periodate oxidation resulted in total loss of its immunodiffusion-TP activity. Analysis of the carbohydrate composition of the TP-Ag revealed xylose, 3-O-methylmannose (3-O-MM), mannose, galactose, and glucose. Competitive inhibition ELISAs were used to demonstrate that 3-O-MM is largely responsible for the reactivity of IgM precipitin antibodies with the 120-kDa TP-Ag. Synthetic 3-O-MM may be a useful probe for detection of anti-Coccidioides precipitin antibodies in the ELISA.     

Purification, characterization, and seroactivity of a 20-kilodalton Brucella protein antigen.

An internal protein was purified from cell extracts of Brucella melitensis B115 by a combination of preparative isoelectric focusing and high-performance size exclusion chromatography. The protein has an apparent molecular mass of 230 kDa as determined by size exclusion chromatography. The protein was resolved to a single band of 20 kDa after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The native protein had an isoelectric point of 4.9. The N-terminal sequence of the 20-kDa protein was determined. The 20-kDa protein has been identified as antigen A-2 with a previously described anti-antigen A-2 serum (B. Stemshorn, K. Nielsen, and B. Samagh, Can. J. Comp. Med. 45:77-81, 1981). Antigen A-2 reacted with sera from infected sheep in immunoblotting and may be useful in developing diagnostic tests for brucellosis.     

Studies on a 14-kilodalton surface protein of Onchocerca microfilariae.

A 14-kDa antigen present on the surface of uterine microfilariae of Onchocerca spp. has been identified using monoclonal antibodies. The antigen was also found in skin microfilariae, but in a masked or cryptic form. A complementary DNA clone encoding the epitope recognised by one of the monoclonal antibodies was identified in a lambda gt11 library. Nucleotide sequencing revealed that the 233-bp cDNA fragment codes for the carboxy-terminus of the antigen. The deduced amino acid sequence consists of three hydrophobic domains with high potential for beta-sheet formation. The amino-terminal hydrophobic domain is followed by 4 positively charged residues (positions 22-25) which contribute to the rather basic character of the protein. Another interesting feature of the polypeptide is its richness in phenylalanine (12.7%). From the sequence information, a synthetic peptide was synthesised which was recognised by one of the monoclonal antibodies directed against the 14-kDa antigen and a small number of sera from patients with onchocerciasis. The relevance of this to vaccination is discussed.     

A novel activation induced lymphocyte surface antigen, 90.12, is also expressed on apoptotic cells

We describe a monoclonal antibody, mAb 90.12, which recognizes a novel activation induced lymphocyte surface antigen. Flow cytometric analysis of normal tissues shows the antigen to be expressed on higher percentages of B lymphocytes in the bone marrow than in the spleen and the lymph node. Similarly, the 90.12 antigen is expressed on higher percentages of thymocytes than peripheral T cells. MAb 90. 12 immunoprecipitates three proteins with a molecular weight of 12-18 kDa which are not linked to the membrane by phosphotidylinositol. Expression of the 90.12 antigen is increased on activated B cells and the extent of upregulation varies with the stimulus. Lipopolysaccharide (LPS) stimulation results in expression on most B cells, while expression is upregulated on only a subset of B cells stimulated with anti-immunoglobulin M (IgM), interleukin(IL)4 and IL5. Finally, we show that 90.12 antigen expression is also increased on apoptotic cells.     

The 39-kilodalton protein of Borrelia burgdorferi: a target for bactericidal human monoclonal antibodies.

Three human monoclonal immunoglobulin M antibodies against Borrelia burgdorferi, obtained from in vitro-stimulated peripheral blood lymphocytes, reacted in Western blots (immunoblots) with a prominent 39-kDa peptide and a faint band of approximately 66 kDa. Two of these antibodies showed bactericidal activity without addition of complement. All three antibodies were reactive in an enzyme immunoassay with cloned P39 (W.J. Simpson, M.E. Schrumpf, and T.G. Schwan, J. Clin. Microbiol. 28:1329-1337, 1990), suggesting that the target molecule of these antibodies is identical to the P39 protein. In addition, the majority of supernatants from human lymphocytes stimulated in vitro with crude B. burgdorferi antigen reacted in this assay, demonstrating that P39, although a minor component of B. burgdorferi, is an immunodominant antigen in these spirochetes. A fourth monoclonal antibody, reacting with OspA, also exhibited bactericidal activity.