Effect of anaerobiosis and nitrate on gene expression in Pseudomonas aeruginosa

DNA microarrays were used to examine the transcriptional response of Pseudomonas aeruginosa to anaerobiosis and nitrate. In response to anaerobic growth, 691 transcripts were differentially expressed. Comparisons of P. aeruginosa grown aerobically in the presence or the absence of nitrate showed differential expression of greater than 900 transcripts.

Recombinant human antibody single chain variable fragments reactive with Candida albicans surface antigens

A combinatorial phage display library expressing human immunoglobulin heavy and light chain variable regions was used to identify phage clones capable of binding to the surface of Candida albicans blastoconidia. Single chain antibody variable fragments (scFv) derived from three clones detected C. albicans antigens by indirect immunofluorescence assay (IFA), enzyme-linked immunosorbent assay (ELISA), and Western blotting. The antigens detected were conserved among different strains of C. albicans and several other Candida species. Two scFv clones detected antigens specifically expressed by C. albicans blastoconidia; the third detected antigens in both blastoconidia and filamentous forms of C. albicans. The antigens containing the epitopes recognized by all three scFv could be extracted from blastoconidia by dithiothreitol, suggesting attachment to the cell wall via sulfhydryl bonds. Epitope detection by the scFv was sensitive to treatment of C. albicans blastoconidia with sodium periodate, but not proteinase K, indicating the cognate epitopes were composed of carbohydrate. Antigenic determinants for each of the three scFv were detected by immunohistochemical staining of skin sections from a model of cutaneous candidiasis, demonstrating expression in vivo. Through selection for the ability to bind intact organisms, the phage display system provides a means to rapidly identify monoclonal binding ligands to Candida surface antigens. Being entirely human, mature antibodies generated from the scFv have potential utility in the treatment of candidiasis.

Recognition elements for 5' exon substrate binding to the Candida albicans group I intron

A group I intron precursor and ribozyme were cloned from the large subunit rRNA of the human pathogen Candida albicans. Both the precursor and ribozyme are functional as determined from in vitro assays. Comparisons of dissociation constants for oligonucleotide binding to the ribozyme and to a hexanucleotide mimic of its internal guide sequence lead to a model for recognition of the 5' exon substrate by this intron. In particular, tertiary contacts with the P1 helix that help align the splice site include three 2'-hydroxyl groups, a G.U pair that occurs at the intron's splice junction, and a G.A pair. The free energy contribution that each interaction contributes to tertiary binding is determined. When the G.A pair is replaced with a G-C pair, tertiary interactions to 5' exon mimic 2'-hydroxyl groups are significantly weakened. When the G.A pair is replaced with a G.U pair, tertiary interactions are retained and binding is 10-fold tighter. These results expand our knowledge of substrate recognition by group I introns, and also provide a basis for rational design of oligonucleotide-based therapeutics for targeting group I introns by binding enhancement by tertiary interactions and suicide inhibition strategies.

Integrin alphavbeta3-mediated endocytosis of immobilized fibrinogen by A549 lung alveolar epithelial cells

Fibrinogen (FBG), together with its polymerized form fibrin, modulates cellular responses during wound repair and tissue remodeling. Thus, we sought to determine whether A549 lung epithelial type II-like cells would endocytose insoluble, surface-bound FBG as a potential mechanism of alveolar matrix remodeling. Surface-bound FBG was endocytosed into either lysosomes or late endosomes by A549 cells through arg-gly-asp-dependent binding to alphavbeta3 but not alpha5beta1 integrin receptors. Soluble FBG added to confluent monolayers of A549 cells was not endocytosed. Unlike the uptake of the extracellular matrix glycoproteins vitronectin and thrombospondin by other cell types, endocytosis of FBG by A549 cells was neither inhibited by heparin nor dependent on binding to cell-surface heparan sulfate proteoglycans. FBG did not colocalize with endocytosed transferrin, whereas dextran showed partial colocalization with FBG in endocytic vesicles, suggesting nonclathrin-mediated endocytosis. Inhibition of actin filament polymerization blocked endocytosis of both dextran and FBG but not transferrin, providing further support that FBG is endocytosed via a nonclathrin pathway. Disruption of actin polymerization inhibited integrin-mediated cell spreading, which contributed to an overall reduction in FBG clearance that was most likely due to reduced cell migration and associated pericellular proteolysis. Trasylol inhibition of extracellular plasmin activity did not inhibit endocytosis of FBG. The endocytosed FBG was degraded to trichloroacetic acid-soluble fragments that showed an electrophoretic pattern distinctly different from plasmin-degraded FBG. Together, these results suggest that endocytosis of matrix-associated FBG by alveolar epithelial cells may be involved in the processes of alveolar tissue repair and matrix remodeling.

Allergens and irritants transcriptionally upregulate CD80 gene expression in human keratinocytes

The human CD80 costimulatory molecule is an important signal between professional antigen-presenting cells and T helper cells. The immunobiology of CD80 expression by keratinocytes, especially during allergic and irritant contact dermatitis, however, is less well understood. CD80 cell surface expression and gene transcription by keratinocytes was increased when keratinocytes were exposed to certain allergens (chemicals that induce inflammation via hapten-specific T cells) and irritants (chemicals that are toxic to epidermal cells). Therefore, the human CD80 promoter was cloned and luciferase reporter constructs containing various promoter fragments were engineered. Promoter mapping of these CD80 constructs in transiently transfected keratinocytes showed that a construct containing the proximal 231 bp immediately upstream of the transcription start site of the CD80 promoter was most active in keratinocytes and was inducible to a level ranging from 2- to 10-fold higher in keratinocytes treated with certain allergens and irritants, compared with untreated keratinocytes. This pattern of promoter fragment activity in keratinocytes is identical to that found in professional antigen-presenting cells. This is the first demonstration that the CD80 promoter is active in keratinocytes and that this activity is further increased in keratinocytes treated with certain allergens and irritants. These data suggest that allergens and irritants may, in part, break peripheral tolerance by their direct effects on keratinocyte costimulatory molecule expression, thereby facilitating interactions with epidermotropic T helper cells via the CD80-CD28 or CTLA-4 pathways.

Molecular characterization of KEX1, a kexin-like protease in mouse Pneumocystis carinii

Expression screening of a Pneumocystis carinii-infected mouse lung cDNA library with specific monoclonal antibodies (mAbs) led to the identification of a P. carinii cDNA with extensive homology to subtilisin-like proteases, particularly fungal kexins and mammalian prohormone convertases. The 3.1 kb cDNA contains a single open reading frame encoding 1011 amino acids. Structural similarities to fungal kexins in the deduced primary amino acid sequence include a putative proenzyme domain delineated by a consensus autocatalytic cleavage site (Arg-Glu-Lys-Arg), conserved Asp, His, Asn and Ser residues in the putative catalytic domain, a hydrophobic transmembrane spanning domain, and a carboxy-terminal cytoplasmic domain with a conserved tyrosine motif thought to be important for localization of the protease in the endoplasmic reticulum and/or Golgi apparatus. Based on these structural similarities and the classification of P. carinii as a fungus, the protease was named KEX1. Southern blotting of mouse P. carinii chromosomes localized kex1 to a single chromosome of approximately 610 kb. Southern blotting of restriction enzyme digests of genomic DNA from P. carinii-infected mouse lung demonstrated that kex1 is a single copy gene. The function of kexins in other fungi suggests that KEX1 may be involved in the post-translational processing and maturation of other P. carinii proteins.

Selected animal models: vaginal candidosis, Pneumocystis pneumonia, dermatophytosis and trichosporosis

A clear understanding of the pathogenesis of fungal disease remains elusive. While technological advances in molecular biology and microbial genetics have provided scientists with major new insights into both microbial virulence factors as well as host susceptibility to infection, there is currently no substitute for animal models in elucidating microbe-host interactions. Animal models are also essential for the evaluation of new antimicrobial agents, including studies of efficacy, adverse reactions and pharmacokinetics. The single most important advance in animal models in the last decade, has been the availability of genetically unique strains of animals as alternative to animals treated with immunosuppressive drugs for use in studies on microbial virulence and host defence mechanisms. These unique strains of test animals also enhance our understanding of the modes of action of antifungal drugs and their metabolism. Some of these advances will be discussed in this symposium.

Antigenic characterization of Pneumocystis carinii

Studies of Pneumocystis carinii have been limited by our inability to propagate it in continuous culture. In this context, studies of P. carinii antigens have provided significant insight into the biology of this organism. The mannose-rich surface major surface glycoprotein of P. carinii termed glycoprotein A (gpA) is the best studied of these P. carinii antigens. Significant genetic and immunologic diversity exists between the gpA molecules expressed by P. carinii derived from different mammalian sources. The molecular and biochemical nature of gpA and other P. carinii antigens including p55 are reviewed. In addition, available information concerning the role of P. carinii gpA and other antigens in host-organism interactions are also discussed.

The carboxyl terminus of Pneumocystis carinii glycoprotein A encodes a functional glycosylphosphatidylinositol signal sequence

Pneumocystis carinii pneumonia is a hallmark disease associated with AIDS. An abundant glycoprotein, termed gpA, on the surface of P. carinii is considered an important factor in host-parasite interactions. The primary structure of ferret P. carinii gpA contains a carboxyl-terminal sequence characteristic of a signal for glycosylphosphatidylinositol (GPI) anchors. Here we report the capacity for this gpA carboxyl sequence to direct attachment of a secreted protein, human growth hormone (hGH), to the membranes of COS cells. A control fusion protein (hGHDAF37) was obtained which, under the direction of the GPI signal from decay accelerating factor, directs hGH cell surface expression. A construct (phGH2-1A30) was created similar to hGHDAF37 by fusing hGH to the putative GPI signal sequence encoded in the terminal 30 residues from a ferret P. carinii gpA cDNA clone. By indirect immunofluorescent staining, hGH was detected on the surface of COS cells transfected with phGH2-1A30; this surface location was confirmed by confocal laser cytometry. Metabolic labeling with [3H]ethanolamine and subsequent immunopurification of hGH from cells transfected with phGH2-1A30 confirmed that a lipid moiety characteristic of a conventional GPI anchor was linked covalently to hGH, and cell surface hGH2-1A30 fusion protein was sensitive to enzymatic cleavage by phosphatidylinositol-phospholipase C. Furthermore, hGH2-1A30 recombinant protein cofractionated with 5'-nucleotidase, a classical GPI-anchored membrane marker. Together, these results indicate that the carboxyl-terminal residues of ferret P. carinii gpA constitute a biologically functional GPI consensus domain, thus providing a potential mechanism for antigenic variation of P. carinii gpA during P. carinii pneumonia.

CD86 (B7-2), but not CD80 (B7-1), expression in the epidermis of transgenic mice enhances the immunogenicity of primary cutaneous Candida albicans infections

Transgenic (Tg) mice whose epidermal keratinocytes constitutively overexpress either B7-1 (CD80) or B7-2 (CD86) exhibited exaggerated cutaneous delayed type hypersensitivity (DTH) to haptens compared to non-Tg mice. To determine whether enhanced DTH in these Tg mice is seen in response to cutaneous fungal infections, a primary infection with Candida albicans was established by inoculating this organism on the occluded skin of Tg and non-Tg mice. These infections resolved 7 days after removal of occlusive dressing in all three groups of mice, without evidence of exaggerated inflammation in either the Tg or non-Tg mice. Only B7-2 Tg mice developed enhanced Th1-lymphocyte-mediated immune responses to C. albicans antigens after resolving this infection: enhanced footpad swelling in response to intradermal C. albicans antigens, enhanced production of mRNA encoding Th1 lymphokines in draining lymph nodes, and increased gamma interferon secreted into culture supernatants by lymph node T lymphocytes stimulated with Candida antigens in vitro. Lastly, Western blotting of sera from mice that had resolved this fungal infection indicated that only B7-2 Tg mice recognized a wide range of Candida-associated antigens. These data suggest that these two costimulatory molecules, when expressed by keratinocytes, do not deliver identical signals to C. albicans antigen-reactive Th1 lymphocytes. The enhanced immune response in B7-2 Tg mice to a cutaneous C. albicans infection demonstrates the importance of antigen presentation and costimulation in immune reactivity to fungi. Furthermore, B7-2 Tg mice may be useful in identification of protective Candida antigens.

Recognition of Pneumocystis carinii antigens by local antibody-secreting cells following resolution of P. carinii pneumonia in mice

To examine the repertoire of Pneumocystis carinii antigens recognized by antibody-secreting B cells from tracheobronchial lymph nodes isolated immediately following recovery from P. carinii pneumonia, monoclonal antibodies (MAbs) were produced from these cells. In contrast to previous studies of systemic immunity, P. carinii gpA was not the immunodominant antigen recognized by these B cells. Forty-nine (91%) of 54 P. carinii-specific hybridoma culture supernatants reacted with P. carinii antigens other than gpA. Many of the resulting MAbs recognized a previously uncharacterized antigen expressed on the surface of both cysts and trophozoites. Western blotting using one of the cloned MAbs revealed reactivity with a broad range of antigenic material, with the most intense reactivity in the 50- to 65-kDa region of the blot. The antigens identified by these MAbs merit further investigation regarding protective immunity to P. carinii because they were recognized by B cells in the context of recovery from P. carinii pneumonia.

Molecular characterization of mouse Pneumocystis carinii surface glycoprotein A

Since the mouse offers an easily manipulated experimental animal model for the study of the immunopathogenesis of pneumonia caused by the opportunist Pneumocystis carinii, we cloned and characterized cDNAs encoding an abundant, immunogenic surface antigen termed glycoprotein A (gpA) from mouse P. carinii. A cDNA library was constructed in bacteriophage lambda gt11 from P. carinii-infected mouse lung poly(A+) RNA. Using a nucleic acid probe derived from a conserved region of the mouse P. carinii gpA structural gene, cDNAs encoding gpA were identified. A composite full-length gpA coding sequence was assembled from two overlapping cDNA clones. A DNA element homologous to the rat P. carinii upstream conserved sequence (UCS) was identified at the 5' end of several of the mouse P. carinii gpA cDNA clones, just upstream of the sequences encoding gpA structural gene isoforms. Using primer extension analysis, two neighboring putative transcriptional start sites were located on UCS-gpA mRNAs approximately 25 and 30 nt, respectively, upstream of the most 5' gpA cDNA clone isolated, suggesting a 5' UCS of 489 or 494 nucleotides in mouse P. carinii gpA. A comparative alignment of the composite mouse P. carinii gpA deduced amino acid sequence with gpA homologs from rat, human and ferret P. carinii demonstrated 156 identical residues, including 46 cysteines, further supporting the hypothesis for conserved secondary structure, as well as function, for gpA from all P. carinii.

Antigenic properties of recombinant glycosylated and nonglycosylated Pneumocystis carinii glycoprotein A polypeptides expressed in baculovirus-infected insect cells

Since a continuous culture system is not yet available for the opportunistic fungal pathogen Pneumocystis carinii, obtaining suitable amounts of purified P. carinii antigens free of mammalian-host lung contaminants is difficult. Hence, production of recombinant antigen possessing epitopes found in native P. carinii antigens is critical for immunological studies. We utilized the baculovirus expression vector system (BEVS) in insect cells to determine whether B-cell epitopes present in the protein core of a native P. carinii surface glycoprotein were conserved in the recombinant polypeptide, and to investigate its glycosylation by insect cells. B-cell epitopes were retained, but the insect cells appeared to hyperglycosylate the recombinant protein.

A Pneumocystis carinii group I intron ribozyme that does not require 2' OH groups on its 5' exon mimic for binding to the catalytic core

The recent increase in the population of immunocompromised patients has led to an insurgence of opportunistic human fungal infections. The lack of effective treatments against some of these pathogens makes it important to develop new therapeutic strategies. One such strategy is to target key RNAs with antisense compounds. We report the development of a model system for studying the potential for antisense targeting of group I self-splicing introns in fungal pathogens. The group I intron from the large ribosomal subunit RNA of mouse-derived Pneumocystis carinii has been isolated and characterized. This intron self-splices in vitro. A catalytically active ribozyme, P-8/4x, has been constructed from this intron to allow measurement of dissociation constants for potential antisense agents. At 37 degrees C, in 50 mM Hepes (25 mM Na+), 15 mM MgCl2, and 135 mM KCl at pH 7.5, the exogenous 5' exon mimic r(AUGACU) binds about 60 000 times more tightly to this ribozyme than to r(GGUCAU), a mimic of its complementary binding site on the ribozyme. This enhanced binding is due to tertiary interactions. This tertiary stabilization is increased by single deoxynucleotide substitutions in the exon mimic at every position except for the internal A, which is essentially unchanged. Thus 2' OH groups of the 5' exon mimic do not form stabilizing tertiary interactions with the P-8/4x ribozyme, in contrast to the Tetrahymena L-21 ScaI ribozyme. Furthermore, at 37 degrees C, the exogenous 5' exon mimic d(ATGACT) binds nearly 32 000 times more tightly to the P-8/4x ribozyme than to r(GGUCAU). Therefore, oligonucleotides without 2' OH groups can exploit tertiary stabilization to bind dramatically more tightly and with more specificity than possible from base pairing. These results suggest a new paradigm for antisense targeting: targeting the tertiary interactions of structural RNAs with short antisense oligonucleotides.

Cloning and characterization of a conserved region of human and rhesus macaque Pneumocystis carinii gpA

Although the genes encoding Pneumocystis carinii (Pc) glycoprotein A (gpA) display a high degree of host species-specific genotypic diversity, the Pc gpA derived from different host species share defined regions of significant homology in their primary amino acid (aa) structure. Using two degenerate oligodeoxyribonucleotide (oligo) primers corresponding to a conserved Cys region (Cys-primers) of the ferret (F), rat (R) and mouse (M) PcgpA, a 306-bp portion of the human (H) PcgpA was amplified from only one of three known HPc-infected lung samples using PCR. The deduced aa sequence of the HPc PCR product was 72% similar to the corresponding region of a published HPc gpA aa sequence. Because the conserved Cys-primers amplified only one of three samples of HPcgpA, a primer-pair was designed from sequences internal to the Cys-primer sequences of the HPcgpA PCR product (hPc). The hPc primers amplified the expected 254-bp product from each of the three HPc-infected lung DNA samples, suggesting that the Cys-primers may have either amplified a HPcgpA present in fewer copies in the genome of HPc or, alternatively, amplified a gene from an uncommon strain of Pc encoding an isoform variant of gpA not present in the other human isolates analyzed in this report. Restriction analysis of the amplified products demonstrated heterogeneity in the internal sequence, confirming that more than one gpA exists in HPc as well. To determine the relationship of HPcgpA to the gpA of Pc from another primate, the hPc primers were used successfully to amplify a 261-bp product from Pc-infected Rhesus macaque (Rm) lung genomic DNA. These results are consistent with our earlier findings that closely related host species are infected with Pc organisms encoding similar gpA, suggesting that the evolutionary divergence of Pc followed that of the mammalian host species.

Interaction of outer envelope proteins of Chlamydia psittaci GPIC with the HeLa cell surface

The chlamydial life cycle involves the intimate interaction of components of the infectious elementary body (EB) surface with receptors on the susceptible eukaryotic cell plasma membrane. We have developed an in vitro ligand binding assay system for the identification and characterization of detergent-extracted EB envelope proteins capable of binding to glutaraldehyde-fixed HeLa cell surfaces. With this assay, the developmentally regulated cysteine-rich envelope protein Omp2 of Chlamydia psittaci strain guinea pig inclusion conjunctivitis was shown to bind specifically to HeLa cells. HeLa cells bound Omp2 selectively over other cell wall-associated proteins, including the major outer membrane protein, and the binding of Omp2 was abolished under conditions which alter its conformation. Furthermore, trypsin treatment, which reduces EB adherence, resulted in the proteolytic removal of a small terminal peptide of Omp2 at the EB surface and inactivated Omp2 in the ligand binding assay, while having a negligible effect on the major outer membrane protein. Collectively, our results suggest that Omp2 possesses the capacity to engage in a specific interaction with the host eukaryotic cell. We speculate that, since Omp2 is present only in the infectious EB form, the observed in vitro interaction may be representative of a determining step of the chlamydial pathogenic process.

Isoform diversity and tandem duplication of the glycoprotein A gene in ferret Pneumocystis carinii

Two ferret P. carinii gpA cDNA clones were identified that reacted identically with a panel of anti-gpA monoclonal antibodies, although their nucleotide sequences were 22% divergent. Each clone hybridized to a single mRNA species of 3,600 nucleotides only in P. carinii-infected lung mRNA, but RT-PCR analysis demonstrated that these cDNA clones were derived from two distinct gpA mRNA transcripts. Further PCR analysis demonstrated that the ferret P. carinii genome contains at least two gpA genes lying in tandem on a single chromosome separated by a 329-bp intergenic region. Based on the terminal gene sequences of this tandem repeat and the cDNA clones, a composite full-length ferret P. carinii gpA coding sequence was constructed. The intergenic region immediately downstream of the stop codon of the first gpA gene contains three putative polyadenylation signals, and constitutes the 3' untranslated region (UTR) of the gpA mRNA. Primer extension of the gpA mRNA resulted in products extending 74 and 244 nucleotides into the 5' UTR. However, the intergenic region lying greater than 25 nucleotides upstream of the first methionine of the second gpA gene was found to be absent from the 5' UTR.

Intracellular localization of a Trypanosoma cruzi kDNA minicircle transcript using RNA: RNA in situ hybridization

Using RNA: RNA in situ hybridization, the intracellular location of a transcript encoded by and spanning the entire length of a Trypanosoma cruzi kinetoplast DNA minicircle was determined. In axenically cultured T. cruzi epimastigotes, the hybridization signal was restricted to the kinetoplast, which was situated in the perinuclear region of the cell. Following conversion of epimastigotes to culture-derived metacyclic trypomastigotes, the kinetoplast moved to an acentric position in the metacyclic trypomastigote. Again, the hybridization signal co-localized with the position of the kinetoplast. These results suggested that the transcript remained closely associated with the T. cruzi kinetoplast within the mitochondrion in each of the morphological forms. Using specific oligonucleotide probes derived from a cDNA encoding the transcript, the entire native kDNA minicircle encoding the transcript was cloned and its nucleotide sequence was determined. The nucleotide sequence of the intact native minicircle was identical to that of the full-length cDNA corresponding to the minicircle transcript, indicating that the transcript was not modified prior to the time of cDNA synthesis and cloning.

Conserved sequence homology of cysteine-rich regions in genes encoding glycoprotein A in Pneumocystis carinii derived from different host species

Pneumocystis carinii surface glycoprotein A (gpA) exhibits host species-specific phenotypic and genotypic variation. Despite this heterogeneity, the gpAs of P. carinii isolated from different host species appear to be homologous molecules sharing certain biochemical and antigenic characteristics. Using two degenerate oligodeoxyribonucleotide primers corresponding to conserved cysteine regions from ferret and rat P. carinii gpAs, a PCR product of approximately 300 bp was amplified from ferret, rat, and SCID mouse P. carinii-infected lung genomic DNA. Northern (RNA) hybridization revealed a transcript of 3,450 nucleotides in P. carinii-infected SCID mouse lung mRNA, which is similar in size to the transcripts for ferret and rat P. carinii gpAs. Nucleotide sequence analysis of SCID mouse P. carinii gpA subclones derived from the PCR products identified two isoforms, which were 89% identical to each other in the amplified region and 73 and 54% identical to the rat- and ferret-derived P. carinii gpA genes, respectively. Comparison of the deduced amino acid sequences of mouse, ferret, and rat P. carinii gpAs revealed striking similarity in residues adjacent to and including the conserved cysteines. Furthermore, the spacing of two proline residues is invariant, and a potential N-linked glycosylation site is found at a similar position in all of the gpAs. Despite the heterogeneity observed in P. carinii gpAs, the conservation of cysteine residues and adjacent sequences implies similar secondary structure and, most likely, similar function for the gpAs of P. carinii isolated from different host species.

Identification and characterization of a Candida albicans-binding proteoglycan secreted from rat submandibular salivary glands

A previously identified Candida albicans-binding glycoprotein secreted from rat submandibular glands (RSMG) has been further purified from an aqueous RSMG extract by ion-exchange chromatography and gel filtration. Biochemical analysis of the glycoprotein revealed high levels of uronic acid and sulfate, suggesting that it was a proteoglycan. Its amino acid and carbohydrate compositions were similar to those observed for other proteoglycans and differed significantly from those of RSMG mucin, the major secretory glycoprotein of RSMG. In addition, the apparent molecular weight of the glycoprotein was reduced following treatment with either chondroitinase ABC or heparitinase, demonstrating the presence of chondroitin sulfate and heparan sulfate. On the basis of its structure and anatomical source, the glycoprotein is referred to as submandibular gland secreted proteoglycan 1 (SGSP1). SGSP1 also binds monoclonal antibody 1F9, which recognizes the human blood group A carbohydrate epitope found on RSMG mucin. Hence, SGSP1 appears to be a hybrid molecule with carbohydrate structures found in both proteoglycans and RSMG mucin. Enzymatic digestion of SGSP1, followed by its interaction with a radiolabelled C. albicans strain in a filter-binding assay, demonstrated that binding to this strain appears to be mediated primarily via the heparan sulfate side chains of SGSP1 and not via the blood group A oligosaccharide.

Further evidence of host species-specific variation in antigens of Pneumocystis carinii using the polymerase chain reaction

To further elucidate the extent of variation among Pneumocystis carinii obtained from different mammalian hosts, polymerase chain reaction (PCR) analysis of the genes encoding two antigens of P. carinii was done. Using primers based on the ferret P. carinii glycoprotein (gp)A gene and the rat P. carinii 45- to 55-kDa antigen gene, amplification was attempted with DNA isolated from P. carinii-infected ferret, rat, mouse, and human lungs. For both genes, amplification was successful only with P. carinii DNA isolated from the same host species from which the P. carinii gene was originally isolated. The presence of P. carinii DNA in each sample was documented by PCR using primers based on the conserved mitochondrial ribosomal RNA gene sequence. These results were confirmed for P. carinii gpA by Southern blot analysis using a labeled fragment of the ferret P. carinii gpA gene as a probe. Thus, in addition to the previously reported phenotypic variation among antigens of P. carinii, there is also genotypic variation of these same antigens.

Pneumocystis carinii is not universally transmissible between mammalian species

In a series of five experiments, we attempted to transmit Pneumocystis carinii from ferrets to SCID mice by intratracheal inoculation. Using highly specific and sensitive assay techniques, we could not document infection of SCID mice by P. carinii isolated from ferrets. In contrast, under identical inoculation conditions, P. carinii was easily transmissible from one SCID mouse to another. These results indicate that P. carinii organisms, at least those isolated from ferrets, have a restricted host range. The finding of restricted transmission of P. carinii is consistent with the increasing evidence for host species-specific antigenic variation among isolates of P. carinii. If restricted host range is a consistent biological feature of animal-derived P. carinii, it would suggest that P. carinii pneumonitis in humans may not be a zoonosis as previously speculated.

Analysis of Candida albicans adhesion to salivary mucin

Clearance of Candida albicans from the oral cavity is thought to be mediated via specific receptor-ligand interactions between salivary constituents and the fungus. Since surfaces in the oral cavity are normally coated with a saliva-derived pellicle, specific interactions between salivary constituents and C. albicans may also contribute to adhesion of C. albicans to the oral mucosa and dental prostheses. Therefore, the purpose of this study was to identify salivary constituents to which C. albicans is capable of binding. A solid-phase overlay assay was used in which electrophoretically separated rat and human salivary constituents bound to membrane filters were incubated with radiolabelled C. albicans cells. C. albicans adhered to a single salivary component from each host. Correlation of cell-binding activity with specific monoclonal antibody (MAb)-binding activity indicated that the constituent bound by C. albicans in human saliva was low-molecular-weight mucin (MG2) and that in rat saliva was rat submandibular gland (RSMG) mucin. Further studies showed an identical cell hybridization signal and MAb colocalization by using RSMG ductal saliva and an aqueous RSMG extract in the solid-phase overlay assay. Analysis of cell binding to the aqueous extract of RSMG fractionated by anion-exchange chromatography demonstrated that C. albicans binding was restricted to an acidic subfraction of the RSMG extract, which also bound the RSMG mucin-specific MAb. The Candida-binding fraction contained predominantly RSMG mucin glycoprotein and also a noncovalently associated, chloroform-extractable material. Furthermore, we identified two strains of C. albicans which differed severalfold in the ability to bind RSMG mucin in the overlay assay. These results suggest that C. albicans binds to only a specific subfraction of RSMG mucin and that the two C. albicans strains tested differ in the ability to bind RSMG mucin subfractions.

In situ hybridization analysis of developmental stages of Pneumocystis carinii that are transcriptionally active for a major surface glycoprotein gene

An abundant glycoprotein on the surface of Pneumocystis carinii, termed gpA or gp120, is thought to play a role in the interaction of this opportunistic pathogen with its host. Using RNA:RNA hybridization techniques, the in situ expression of gpA mRNA in developmental forms of the organism was investigated in a ferret model of P. carinii pneumonia. The results suggested that the relative abundance of gpA-specific mRNA was variable in different developmental stages of ferret P. carinii. P. carinii localized along the epithelial lining of alveoli were transcriptionally active. Immunocytochemical detection of gpA and Giemsa staining suggested that many of these organisms were trophic forms of P. carinii. While no detectable gpA mRNA signal was found in the majority of P. carinii cysts, a portion of identifiable cysts co-localized with significant levels of gpA mRNA signal. Differential staining of the cyst wall with Gomori's methenamine silver suggested that the transcriptionally active P. carinii cysts were the intermediate or precyst forms of the organism, while the cysts with no detectable mRNA signal were either mature or empty (excysted). Alveolar macrophages were observed surrounded by transcriptionally active organisms; however, no gpA-transcriptional activity was detected within macrophages. Taken together, the results suggest that transcription of gpA occurs in forms of P. carinii that are actively replicating, and in close proximity or contact with, alveolar epithelial cells.

Expression and characterization of a cDNA clone encoding an immunodominant surface glycoprotein of Pneumocystis carinii

Most studies of antigens of Pneumocystis carinii have focused on an abundant, immunogenic 95- to 140-kDa surface glycoprotein referred to as gpA. Expression cloning of gpA from P. carinii obtained from ferrets resulted in isolation of colinear fragments of gpA cDNA encoding approximately 87 kDa of the core protein. Northern hybridization detected an abundant, single species of gpA-specific mRNA of 3600 nucleotides. Southern hybridization revealed gpA-specific bands only in P. carinii-infected lung genomic DNA, suggesting that gpA cDNA did not result from induction of a host lung gene. Antiserum raised against a fragment of recombinant gpA detected P. carinii cysts and isolated native P. carinii gpA, indicating retention of epitopes between the nonglycosylated recombinant gpA and glycosylated native gpA. The deduced amino acid sequence is hydrophilic and contains 12 potential N-linked glycosylation sites and 47 cysteine residues, consistent with the surface orientation of gpA on the organism and other known characteristics of the native molecule.

The influence of morphological variation on Candida albicans adhesion to denture acrylic in vitro

Using denture acrylic pieces coated with either whole human stimulated saliva or oral streptococci, the binding ability of three different Candida albicans strains was investigated. The C. albicans strains include a clinical isolate with the commonly observed, smooth, round colonial morphology (strain 613p), a morphological variant spontaneously derived from the clinical isolate strain 613p (strain 613m1BK) and a clinical isolate from an oral lesion that was also a morphological variant upon primary isolation (strain 228). Levels of adhesion to the acrylic pieces were determined radiometrically using C. albicans cells metabolically labelled with [35S]-methionine. Whole stimulated saliva significantly increased the binding of all strains compared to uncoated acrylic. However, the level of binding of strain 613p to saliva-coated acrylic was significantly greater than the levels observed for the morphological variant strain 613m1BK. Coating acrylic pieces with either Streptococcus sanguis NCTC 10904, Strep. mutans GS-5 or Strep. sobrinus ATCC 27352 instead of saliva resulted in significantly greater binding by strain 613p compared to uncoated acrylic. Pre-coating the acrylic with the oral streptococci did not significantly increase the binding of morphological variant strains 613m1BK and 228 compared to uncoated acrylic. In general, preincubation of adherent streptococci with sucrose to induce the synthesis of extracellular carbohydrate polymers did not significantly increase the binding levels of the C. albicans strains above those observed using streptococci in buffer alone. Compared to its parental strain 613p, morphological variant strain 613m1BK adhered poorly to denture acrylic coated with either salivary constituents or oral streptococci, while strain 228 adhered to the same substrates at an intermediate level. Furthermore, physical disaggregation of clusters of the morphological variant strain 613m1BK did not appear to increase its binding capacity to saliva-coated denture acrylic. The effect of whole stimulated saliva on the adherence of C. albicans 613p to a variety of plastic substrates in addition to denture acrylic was examined. Overall, saliva pre-coating of the various plastics promoted C. albicans 613p adhesion. The adhesion of strain 613p to denture acrylic coated with whole stimulated saliva from each of five different donors or with parotid and submandibular/sublingual saliva from each of two donors was also examined. Regardless of donor, a coating of whole stimulated saliva significantly increased the binding of strain 613p to denture acrylic compared to uncoated acrylic. In addition, a coating of parotid saliva significantly increased the binding of strain 613p to denture acrylic compared to submandibular/sublingual saliva.

Evidence that the entire length of a kinetoplast DNA minicircle is transcribed in Trypanosoma cruzi

A 1.3 kb cDNA (cDNA52) was derived from Trypanosoma cruzi trypomastigote mRNA. Using single stranded probes in Northern blots, we identified the putative coding strand of cDNA52. In addition, a minor band was detected in RNA from epimastigotes that was absent in RNA from trypomastigotes. Nucleotide sequence analysis revealed that cDNA52 was highly homologous to T. cruzi kinetoplast DNA minicircle sequences. All four conserved regions of T. cruzi minicircles were identified in cDNA52. Using several criteria, we demonstrated that the hybridization signals were not caused by contaminating minicircle DNA in the RNA preparations. The data provide direct evidence for the unprecedented finding that the entire length of a kDNA minicircle is transcribed in T. cruzi.

Oral and esophageal Candida albicans infection in hyposalivatory rats

The opportunistic fungus Candida albicans is a major cause of oral and esophageal infections in immuno-compromised patients, individuals on drug therapy, and the chronically ill. Because it has been observed that persons suffering from hyposalivation have an increased prevalence of oral candididiasis, we developed an animal model of infection based on hyposalivation. The objectives of our studies were to understand the mechanisms by which C. albicans causes oral disease and to begin to elucidate the role played by saliva in controlling C. albicans in the oral cavity. Our results showed that (i) oral Candida infection was established by a small challenge inoculum, (ii) mucosal lesions developed in the oral cavities and esophagi of infected rats, and (iii) transmission of oral Candida infection from an inoculated rat to uninoculated cagemates occurred rapidly. In addition, we compared the abilities of a clinical isolate and a spontaneously derived morphological mutant from that isolate to infect hyposalivatory rats and to induce disease. Infection was induced by the morphological mutant in hyposalivatory rats; however, the morphological mutant took significantly longer to transmit oral infection to uninoculated cagemates than did the parental strain.

Purification and characterization of stage-specific glycoproteins from Trypanosoma cruzi

Four developmentally regulated glycoproteins were purified from detergent solubilized cell membranes of Trypanosoma cruzi. Three trypomastigote specific glycoproteins each migrated as single bands under denaturing conditions with approximate Mr of 90,000, 85,000, and 55,000 and pI values of 4.3-5.0, 8.5-9.1, and 8.2, respectively. The fourth, epimastigote specific, protein had an approximate Mr of 72,000 and a pI of 4.8-5.1. The Mr of all four glycoproteins changed by 5-50% upon endoglycosidase F treatment. The Mr 72,000 antigen was the only one that reacted strongly with anti-epimastigote sera raised in rabbits. Sera from a Chagasic patient reacted strongly with the three trypomastigote specific glycoproteins and very weakly with the Mr 72,000 glycoprotein.

Neuraminidase from Trypanosoma cruzi: analysis of enhanced expression of the enzyme in infectious forms

We purified the neuraminidase (sialidase, acylneuraminyl hydrolase, EC 3.2.1.18) from the protozoan parasite Trypanosoma cruzi, strain Y, and examined the developmental regulation of the enzyme. The detectable amount of enzyme activity increased 10- to 20-fold upon conversion of the parasite from the noninfectious epimastigote form to the infectious trypomastigote form. The enzyme was purified from membranes of trypomastigotes greater than 5000-fold to apparent homogeneity and migrated as an entity of Mr 60,000 under denaturing conditions. Antibodies produced in rabbits against the denatured protein recognized the neuraminidase in membrane extracts from the infectious stage but not from the noninfectious stage. Sera from a patient with acute chagasic disease also reacted strongly with the neuraminidase. Other T. cruzi strains exhibited similar neuraminidase activities and induction rates. The coincidence of infectivity and enhanced expression of neuraminidase in trypomastigotes suggests that this enzyme constitutes a virulence factor in T. cruzi.

Monoclonal antibody characterization of the 195-kilodalton major surface glycoprotein of Plasmodium falciparum malaria schizonts and merozoites: identification of additional processed products and a serotype-restricted repetitive epitope

The gp195 from Camp strain parasites was characterized with eight monoclonal antibodies (MAb) that recognize different epitopes on gp195 and three of its merozoite-associated processed products. Four MAb (3H7, 3B10, 7F1, and 4G12) reacted with different epitopes on the 45-kDa glycosylated product (gp45), shown by differences in their reactivities with soluble and immunoblotted gp45. One MAb (7H10) reacted with a conformational epitope probably formed as a result of the interaction of gp45 with a nonglycosylated 45-kDa product (p45). Three other MAb (3D3, 7B11, and 7B2) reacted with different epitopes on a nonglycosylated 83-kDa product (p83), shown by differences in their reactivities against various parasite isolates in immunofluorescent antibody assays. Immunoprecipitation of antigens that were pulse-labeled with [3H]isoleucine and chased with cold isoleucine showed that p45 and gp45 were processed products of gp195 and p83 was sequentially processed into smaller fragments of 73 and 67 kDa (p73 and p67). Immunoblots showed that the 7B11 and 7B2 epitopes were present on p83, p73, and p67, but that the 3D3 epitope was present only on p83 and p73. A two-site immunoassay showed the 3D3 epitope to be repetitive. The 3D3 and 7B11 epitopes were serotype restricted (present in seven and 24 of 33 isolates, respectively), but the other five epitopes were common to all isolates tested. The gp195 and its processed products have Mr that are consistent with the Mr of a number of antigens shown previously to be associated with the immune complexes that are formed when merozoites are agglutinated by antibodies contained in some growth inhibitory immune sera.

Monoclonal antibody characterization of the 195-kilodalton major surface glycoprotein of Plasmodium falciparum malaria schizonts and merozoites: identification of additional processed products and a serotype-restricted repetitive epitope

The gp195 from Camp strain parasites was characterized with eight monoclonal antibodies (MAb) that recognize different epitopes on gp195 and three of its merozoite-associated processed products. Four MAb (3H7, 3B10, 7F1, and 4G12) reacted with different epitopes on the 45-kDa glycosylated product (gp45), shown by differences in their reactivities with soluble and immunoblotted gp45. One MAb (7H10) reacted with a conformational epitope probably formed as a result of the interaction of gp45 with a nonglycosylated 45-kDa product (p45). Three other MAb (3D3, 7B11, and 7B2) reacted with different epitopes on a nonglycosylated 83-kDa product (p83), shown by differences in their reactivities against various parasite isolates in immunofluorescent antibody assays. Immunoprecipitation of antigens that were pulse-labeled with [3H]isoleucine and chased with cold isoleucine showed that p45 and gp45 were processed products of gp195 and p83 was sequentially processed into smaller fragments of 73 and 67 kDa (p73 and p67). Immunoblots showed that the 7B11 and 7B2 epitopes were present on p83, p73, and p67, but that the 3D3 epitope was present only on p83 and p73. A two-site immunoassay showed the 3D3 epitope to be repetitive. The 3D3 and 7B11 epitopes were serotype restricted (present in seven and 24 of 33 isolates, respectively), but the other five epitopes were common to all isolates tested. The gp195 and its processed products have Mr that are consistent with the Mr of a number of antigens shown previously to be associated with the immune complexes that are formed when merozoites are agglutinated by antibodies contained in some growth inhibitory immune sera.

Mutants of Salmonella typhimurium that cannot survive within the macrophage are avirulent

Salmonella typhimurium is a facultative intracellular pathogen capable of surviving within phagocytic cells of the reticuloendothelial system. To identify the genes important for intracellular survival, 9516 independent Tn10 insertional mutations were isolated in a virulent strain of S. typhimurium. By using an in vitro assay for survival within macrophages, 83 Tn10 mutants have been identified that have a diminished capacity for intracellular survival (designated MS or macrophage survival mutants). All of the MS mutants are less virulent than the parent strain in vivo, demonstrating that, for Salmonella, survival within the macrophage is essential for virulence. Thirty-seven of the MS mutants have been characterized as to their phenotype, including several mutations that confer sensitivity to specific microbiocidal mechanisms of the macrophage.

Serum containing tumor necrosis factor is cytotoxic for the human malaria parasite Plasmodium falciparum

Sera (BCG-lipopolysaccharide [LPS] serum) were obtained from mice infected with Mycobacterium bovis BCG 2 h after intravenous administration of bacterial endotoxin (LPS). Varying concentrations of sera were added to cultures of Plasmodium falciparum-infected human erythrocytes; parasite viability was assessed by hypoxanthine incorporation after 4 days in culture. At concentrations of 1 to 3%, cultures treated with BCG-LPS serum showed a two- to threefold increase in hypoxanthine incorporation; at higher concentrations (4 to 8%), hypoxanthine incorporation fell to 2 to 5% of that in control cultures. Concurrent assays with control sera (from untreated mice or mice treated with BCG or LPS alone) caused some stimulation but no inhibition at up to 8% concentration. Examination of cultures treated with BCG-LPS serum showed morphological, deterioration of parasites within erythrocytes. The presence of tumor necrosis factor in the BCG-LPS serum was confirmed by using a standard L-cell cytotoxicity assay. In addition, rabbit antiserum against partially purified tumor necrosis factor protected intraerythrocytic forms of P. falciparum from the toxic effects of BCG-LPS serum. These data suggest that the factor in BCG-LPS serum that is toxic to P. falciparum in human erythrocytes is antigenically similar or identical to tumor necrosis factor. This nonantibody mediator of killing may play a role in human malaria.

Efficacy of combined immunostimulation and chemotherapy in experimental visceral Leishmaniasis

A regimen of combined immunostimulation and chemotherapy for the elimination of Leishmania donovani amastigotes was evaluated. An in vitro experimental model utilized cultured peritoneal macrophages from C57B1/6 mice infected with L. donovani tissue forms. Partial or complete activation of macrophages as judged by killing of tumor cells significantly enhanced the efficacy of sodium antimony gluconate (Pentostam). The quantity of drug required for elimination of parasites from immunostimulated cells was considerably lower than that required to achieve comparable amastigote killing in thioglycolate-elicited macrophages. In contrast, amphotericin B cleared infected cells of amastigotes at comparable drug levels when tested with immunostimulated and unstimulated macrophages. Several drugs tested inhibited the conversion of amastigotes to promastigotes in vitro but were ineffective in killing of intracellular tissue forms. Allopurinol and difluoromethylornithine (DMFO) blocked amastigote conversion significantly. These drugs at high concentrations, however, exerted only minimal toxicity for amastigotes residing within macrophages. Efficacy of combined therapy was also demonstrated in vivo. Immunoenhancement of L. donovani-infected mice with Corynebacterium parvum vaccine combined with a regimen of sodium antimony gluconate was significantly more effective than was immunotherapy or drug therapy alone.

A role for oxygen-dependent mechanisms in killing of Leishmania donovani tissue forms by activated macrophages

Leishmania donovani, the causative agent of visceral leishmaniasis, infects macrophages (M phi ) of susceptible vertebrates. Immunologically activated M phi are leishmanicidal, but the mechanisms involved in the killing process are not well defined. We sought to investigate the role of reactive oxygen intermediates in the killing of L. donovani. Both the free-swimming promastigote and the intracellular amastigote forms were found to be susceptible to killing in vitro by hydrogen peroxide and other oxygen intermediates. Upon phagocytosis by mouse peritoneal M phi, promastigotes elicited a significantly stronger respiratory burst compared with amastigotes as measured by release of superoxide anion. Although amastigotes do not elicit a strong burst of M phi oxidative metabolism during the initial phagocytic event, immunologically activated M phi that acquired leishmanicidal capacity could be triggered to release substantial amounts of H2O2. Hence, the development of leishmanicidal capacity was correlated temporally with enhanced H2O2 generation by the M phi. In contrast, M phi that lost their ability to release significant amounts of H2O2 after several days in culture were unable to eliminate their parasite burden. Catalase markedly inhibited the elimination of amastigotes by lymphokine-stimulated M phi. In toto, the results implicate reactive oxygen intermediates in killing of the tissue form of L. donovani by its host cell, the mononuclear phagocyte.

A role for oxygen-dependent mechanisms in killing of Leishmania donovani tissue forms by activated macrophages

Leishmania donovani, the causative agent of visceral leishmaniasis, infects macrophages (M phi ) of susceptible vertebrates. Immunologically activated M phi are leishmanicidal, but the mechanisms involved in the killing process are not well defined. We sought to investigate the role of reactive oxygen intermediates in the killing of L. donovani. Both the free-swimming promastigote and the intracellular amastigote forms were found to be susceptible to killing in vitro by hydrogen peroxide and other oxygen intermediates. Upon phagocytosis by mouse peritoneal M phi, promastigotes elicited a significantly stronger respiratory burst compared with amastigotes as measured by release of superoxide anion. Although amastigotes do not elicit a strong burst of M phi oxidative metabolism during the initial phagocytic event, immunologically activated M phi that acquired leishmanicidal capacity could be triggered to release substantial amounts of H2O2. Hence, the development of leishmanicidal capacity was correlated temporally with enhanced H2O2 generation by the M phi. In contrast, M phi that lost their ability to release significant amounts of H2O2 after several days in culture were unable to eliminate their parasite burden. Catalase markedly inhibited the elimination of amastigotes by lymphokine-stimulated M phi. In toto, the results implicate reactive oxygen intermediates in killing of the tissue form of L. donovani by its host cell, the mononuclear phagocyte.

Elimination of Leishmania donovani amastigotes by activated macrophages

Tissue macrophages are the obligatory host cells for Leishmania donovani, the causative agent of visceral leishmaniasis. In this study we sought to determine whether activated macrophages, as defined by the functional criterion of tumor cell cytotoxicity, were also able to exert a microbicidal effect on ingested L. donovani amastigotes. We found that mouse peritoneal macrophages activated by a variety of means exerted a cytotoxic effect on tumor cell targets but were not able to kill L. donovani amastigotes unless the infected macrophages were exposed continually to an activating stimulus. Corynebacterium parvum, Mycobacterium tuberculosis H37Ra, and lymphokine-activated peritoneal macrophages from C57BL/6J mice were cytotoxic for EMT6 tumor cell targets. However, L. donovani Sudan strain 1S amastigotes were not killed by these macrophages unless the activated state was maintained by daily addition of lymphokine to the infected monolayers for several days postinfection. The killing of amastigotes was dependent on the time of exposure to lymphokine, as well as on the concentration of lymphokine added to the culture.

Experimental studies of the pathogenesis of infections due to Pseudomonas aeruginosa: extracellular protease and elastase as in vivo virulence factors

The effects on mortality of supplemental injections of protease and elastase were determined in burned mice infected with non-lethal inocula of a toxin-producing but non-proteolytic-enzyme-producing strain of Pseudomonas aeruginosa. When a variety of solutions containing proteolytic enzyme were injected under these conditions, the mortality increased significantly. This did not occur when organisms other than P. aeruginosa were used. Injections of the enzyme solutions alone were non-lethal. Injection of a solution of alpha 2-macroglobulin, which was shown to inhibit proteolytic activity, together with a proteolytic enzyme--toxin producing strain of P. aeruginosa caused a significant delay in mortality when compared with controls. It was concluded that protease, elastase, and toxin production were necessary for P. aeruginosa to express full virulence in the burned mouse model.