Myeloid/Lymphoid Neoplasm with FGFR1 Rearrangement Presenting with Polycythemia Vera and T-cell Acute Lymphoblastic Leukemia

Myeloid/lymphoid neoplasm with fibroblast growth factor 1 rearrangements (MLN-FGFR1) represents a rare group of hematologic neoplasms, with approximately 100 cases reported to date. A 69-year-old woman with a history of polycythemia and leukocytosis, with negative molecular testing for JAK2, CALR, and MPL, presented with diffuse adenopathy. A lymph node (LN) biopsy revealed effacement by T-lymphoblasts, consistent with T-cell acute lymphoblastic lymphoma (T-ALL). A staging bone marrow (BM) biopsy demonstrated trilineage hyperplasia, which, taken together with the patient's elevated hemoglobin and low serum erythropoietin level, fulfilled diagnostic criteria for polycythemia vera. Karyotype and fluorescence in situ hybridization on both the BM and LN demonstrated a FGFR1 rearrangement due to t(8;13), consistent with MLN-FGFR1. Whole genome sequencing on the LN additionally identified a pathogenic frameshift mutation of ASXL1 NC_000020.11:g32434646dup NM_015338.6(ASXL1):c.1934dup p.(Gly646Trpfs) predicted to result in loss of protein function, a finding also observed in 8.1% of BM reads. Both the BM and LN harbored missense variants in HDAC4 NM_001378414.1(HDAC4):c.[2763G>A]; [2763=] p.(Met921Ile) and CHEK2 NM_007194.4(CHEK2):c.[538C>T];[538=] p.(Arg180Cys), with an unknown significance. Despite initial response to Mini-CVD + venetoclax, the patient subsequently experienced rapid clinical deterioration and death. We report the second case of MLN-FGFR1 with an ASXL1 mutation and the first case with HDAC4 and CHEK2 variants.

Secretory component mediates Candida albicans binding to epithelial cells

OBJECTIVES

Candida albicans attaches to oral surfaces via a number of mechanisms including adherence mediated by salivary components adsorbed to the C. albicans cell surface. Our goal was to identify the salivary molecules involved.

MATERIALS AND METHODS

Biotinylated salivary polypeptides that were bound by C. albicans were detected in extracts from washed, saliva-treated yeast cells by polyacrylamide gel electrophoresis and electroblot or immunoblot transfer analysis and purified by electroelution. Purified material was tested for the ability to promote the adherence of radiolabelled C. albicans yeast cells to cultured epithelial monolayers.

RESULTS

Three of the polypeptides bound by C. albicans cells were identified as components of secretory IgA, including secretory component. Using non-denaturing polyacrylamide gel electrophoresis, we demonstrated that secretory component could be detected in its free form in saliva, and was bound by yeast cells. Secretory component which was purified by electroelution from non-denaturing PAGE-separated saliva, without detectable complete IgA, promoted adherence of yeast cells to cultured epithelial monolayers in a dose-dependent fashion.

CONCLUSION

These results indicate that despite the inhibitory effect on adherence of IgA specific to C. albicans, IgA components, in particular secretory component, also promote binding to cultured epithelial monolayers.

Pulmonary Microscopic Polyangiitis Presenting as Acute Respiratory Failure from Diffuse Alveolar Hemorrhage

Microscopic polyangiitis and granulomatosis with polyangiitis are rare anti-neutrophilic cytoplasmic antibody-associated systemic vasculitides that predominantly affect small to medium sized vessels of the lungs and kidneys. These syndromes are largely confined to older adults and often present sub-acutely following weeks to months of nonspecific prodromal symptoms. While both diseases often manifest within multiple organ systems concurrently, the disease spectrum of microscopic polyangiitis almost always includes the kidneys, while granulomatosis with polyangiitis is most commonly associated with pulmonary disease. We present two cases of rapid onset respiratory failure secondary to diffuse alveolar hemorrhage in young active duty military personnel. After serological testing and surgical lung biopsy, both patients were diagnosed with microscopic polyangiitis with isolated pulmonary involvement.

Overexpression of Candida albicans CDR1, CDR2, or MDR1 does not produce significant changes in echinocandin susceptibility

The micafungin and caspofungin susceptibilities of Candida albicans laboratory and clinical isolates and of Saccharomyces cerevisiae strains stably hyperexpressing fungal ATP-binding cassette (ABC) or major facilitator superfamily (MFS) transporters involved in azole resistance were determined using three separate methods. Yeast strains hyperexpressing individual alleles of ABC transporters or an MFS transporter from C. albicans gave the expected resistance profiles for the azoles fluconazole, itraconazole, and voriconazole. The strains hyperexpressing CDR2 showed slightly decreased susceptibility to caspofungin in agar plate drug resistance assays, as previously reported, but increased susceptibility to micafungin compared with either the strains hyperexpressing CDR1 or the null parent deleted of seven ABC transporters. The strains hyperexpressing CDR1 showed slightly decreased susceptibility to micafungin in these assays. A C. albicans clinical isolate overexpressing both Cdr1p and Cdr2p relative to its azole-sensitive isogenic progenitor acquired resistance to azole drugs and showed reduced susceptibility to caspofungin and slightly increased susceptibility to micafungin in agar plate drug resistance assays. None of the strains showed significant resistance to micafungin or caspofungin in liquid microdilution susceptibility assays. The antifungal activities of micafungin and caspofungin were similar in agarose diffusion assays, although the shape and size of the caspofungin inhibitory zones were affected by medium composition. The assessment of micafungin and caspofungin potency is therefore assay dependent; the differences seen with agar plate drug resistance assays occur over narrow ranges of echinocandin concentrations and are not of clinical significance.

Characterization of two Candida albicans surface mannoprotein adhesins that bind immobilized saliva components

Salivary components, including the basic proline-rich proteins (bPRP), act as receptors for the adherence of Candida albicans, and this interaction may be important for oral colonization and the development of mucosal Candida infections. Treatment of C. albicans cells with agents affecting either proteinacious or carbohydrate surface macromolecules reduced their adherence in in vitro assays of C. albicans adherence to saliva-coated hydroxyapatite beads and to membrane-immobilized salivary bPRP. In order to identify C. albicans adhesins that bind saliva receptors, yeast cell surface material was extracted by mild glucanase treatment, and was shown to competitively inhibit ( > 50%) the adherence of C. albicans yeast cells in both assays. Concanavalin A sepharose affinity chromatography was used to partially purify glycosylated components of the extract, and two polypeptides (97.4 and 35 kDa) were further purified by preparative SDS PAGE separation and electro-elution. The 97.4 and 35 kDa polypetides each possessed greater adherence-inhibitory specific activity (> 100-fold and > 30-fold respectively) than the original glucanase extract from C. albicans yeast cells. The 35 kDa putative surface protein was identified by N-terminal sequencing and immunoblotting, as the 1,3-beta glucosyltransferase, Bgl2p.

Saliva promotes Candida albicans adherence to human epithelial cells

Adhesion of Candida cells to oral surfaces is an initial event in pathogenesis. Since specific immobilized salivary components mediate the binding of Candida albicans to hydroxyapatite, we hypothesized that saliva may also promote adherence to oral epithelia via a similar mechanism. In an in vitro model, C. albicans ATCC 10261 yeast cells adhered in a saturable manner to monolayers of three cultured human epithelial cell lines (A549, HEp-2, and HET-1A). The addition of whole saliva to the assay promoted the binding of C. albicans to all cell lines in a dose-dependent manner, but pre-incubation of the epithelial cells with pooled whole saliva had no effect on subsequent adherence. Pre-incubation of the yeast cells with pooled whole saliva, however, significantly enhanced (by up to 120%, P < 0.05) binding to epithelial cell monolayers, and pooled saliva that had been pre-incubated with C. albicans yeast cells was defective in promoting yeast adherence. There was a negative correlation (r = 0.68, P < 0.005) between specific IgA titers against whole cells of C. albicans and adherence-promoting activities for individual saliva samples. The adhesion-inhibitory effect of specific anti-C. albicans IgA was reversed by depletion of IgA from saliva by affinity chromatography. Factors in whole saliva, therefore, bound to the yeast cells, counter the C. albicans-specific salivary IgA inhibitory effect on adhesion and promote the adherence of C. albicans yeast cells to cultured epithelial cells.

Functional expression of Candida albicans drug efflux pump Cdr1p in a Saccharomyces cerevisiae strain deficient in membrane transporters

Analysis of the transport functions of individual Candida albicans plasma membrane drug efflux pumps is hampered by the multitude of endogenous transporters. We have stably expressed C. albicans Cdr1p, the major pump implicated in multiple-drug-resistance phenotypes, from the genomic PDR5 locus in a Saccharomyces cerevisiae mutant (AD1-8u(-)) from which seven major transporters of the ATP-binding cassette (ABC) family have been deleted. High-level expression of Cdr1p, under the control of the S. cerevisiae PDR5 promoter and driven by S. cerevisiae Pdr1p transcriptional regulator mutation pdr1-3, was demonstrated by increased levels of mRNA transcription, increased levels of nucleoside triphosphatase activity, and immunodetection in plasma membrane fractions. S. cerevisiae AD1-8u(-) was hypersensitive to azole antifungals (the MICs at which 80% of cells were inhibited [MIC(80)s] were 0.625 microg/ml for fluconazole, <0.016 microg/ml for ketoconazole, and <0.016 microg/ml for itraconazole), whereas the strain (AD1002) that overexpressed C. albicans Cdr1p was resistant to azoles (MIC(80)s of fluconazole, ketoconazole, and itraconazole, 30, 0.5, and 4 microg/ml, respectively). Drug resistance correlated with energy-dependent drug efflux. AD1002 demonstrated resistance to a variety of structurally unrelated chemicals which are potential drug pump substrates. The controlled overexpression of C. albicans Cdr1p in an S. cerevisiae background deficient in other pumps allows the functional analysis of pumping specificity and mechanisms of a major ABC transporter involved in drug efflux from an important human pathogen.

The pavA gene of Streptococcus pneumoniae encodes a fibronectin-binding protein that is essential for virulence

Streptococcus pneumoniae colonizes the nasopharynx in up to 40% of healthy subjects, and is a leading cause of middle ear infections (otitis media), meningitis and pneumonia. Pneumococci adhere to glycosidic receptors on epithelial cells and to immobilized fibronectin, but the bacterial adhesins mediating these reactions are largely uncharacterized. In this report we describe a novel pneumococcal protein PavA, which binds fibronectin and is associated with pneumococcal adhesion and virulence. The pavA gene, present in 64 independent isolates of S. pneumoniae tested, encodes a 551 amino acid residue polypeptide with 67% identical amino acid sequence to Fbp54 protein in Streptococcus pyogenes. PavA localized to the pneumococcal cell outer surface, as demonstrated by immunoelectron microscopy, despite lack of conventional secretory or cell-surface anchorage signals within the primary sequence. Full-length recombinant PavA polypeptide bound to immobilized human fibronectin in preference to fluid-phase fibronectin, in a heparin-sensitive interaction, and blocked binding of wild-type pneumococcal cells to fibronectin. However, a C-terminally truncated PavA' polypeptide (362 aa residues) failed to bind fibronectin or block pneumococcal cell adhesion. Expression of pavA in Enterococcus faecalis JH2-2 conferred > sixfold increased cell adhesion levels to fibronectin over control JH2-2 cells. Isogenic mutants of S. pneumoniae, either abrogated in PavA expression or producing a 42 kDa C-terminally truncated protein, showed up to 50% reduced binding to immobilized fibronectin. Inactivation of pavA had no effects on growth rate, cell morphology, cell-surface physico-chemical properties, production of pneumolysin, autolysin, or surface proteins PspA and PsaA. Isogenic pavA mutants of encapsulated S. pneumoniae D39 were approximately 104-fold attenuated in virulence in the mouse sepsis model. These results provide evidence that PavA fibronectin-binding protein plays a direct role in the pathogenesis of pneumococcal infections.

Transfer and expression of foreign genes in mammalian cells

The transfer of foreign genes into eukaryotic cells, in particular mammalian cells, has been essential to our understanding of the functional significance of genes and regulatory sequences as well as the development of gene therapy strategies. To this end, different mammalian expression vector systems have been designed. The choice of a particular expression system depends on the nature and purpose of the study and will involve selecting particular parameters of expression systems such as the type of promoter/enhancer sequences, the type of expression (transient versus stable) and the level of desired expression. In addition, the success of the study depends on efficient gene transfer. The purification of the expression vectors, as well as the transfer method, affects transfection efficiency. Numerous approaches have been developed to facilitate the transfer of genes into cells via physical, chemical or viral strategies. While these systems have all been effective in vitro they need to be optimized for individual cell types and, in particular, for in vivo transfection.

Intracellular compartmentalization of DNA fragments in cultured airway epithelial cells mediated by cationic lipids

PURPOSE

The amount and intracellular distribution of DNA fragments (491-bp) was characterized after transfection in vitro with a commercially available cationic lipid. Localization of fragment to the nucleus, its subcellular distribution, and integrity within the cells was determined for various times after transfection.

METHODS

Cystic fibrosis (CF) airway epithelial cells were transfected with 32P and FITC labeled single-stranded (ss) or double-stranded (ds) DNA fragments complexed with Lipofectamine at various charge ratios.

RESULTS

A 511 (+/-) charge ratio was found to be the optimal ratio for transfection of both ss-and dsDNA. After a 5 h exposure, 7.51 +/- 0.89% of the radioactivity was associated with the nuclear fraction whereas only 1.07 +/- 0.23%, was found in the nuclear fraction when dsDNA was used. The nuclear radioactivity detected after a 24 h exposure was only 1/3 of that after 5 h. Analysis of fragment stability in the cytosolic and nuclear fractions showed the presence of intact fragment in each subcellular compartment. No intranuclear/intracellular fragment could be detected in control experiments with naked DNA. Conclusions. The results from these experiments indicate that small fragments of DNA can be efficiently and rapidly transferred intact to the cell nucleus using cationic lipids and that ssDNA fragments are more effective than dsDNA fragments for nuclear delivery.

Binding properties of Streptococcus gordonii SspA and SspB (antigen I/II family) polypeptides expressed on the cell surface of Lactococcus lactis MG1363

The oral bacterium Streptococcus gordonii expresses two cell wall-associated polypeptides, designated SspA (1,542 amino acid residues) and SspB (1,462 amino acid residues), that have 70% sequence identity. These polypeptides are members of the antigen I/II family of oral streptococcal adhesins and mediate the binding of streptococci to salivary glycoproteins, collagen, and other oral microorganisms such as Actinomyces naeslundii. To determine if SspA and SspB have differential binding properties, the coding sequences of the sspA and sspB genes were cloned into expression plasmid vector pTREX1-usp45LS to generate pTREX1-sspA and pTREX1-sspB, respectively, and the Ssp polypeptides were displayed on the cell surface of Lactococcus lactis MG1363. Lactococcal cells expressing similar levels of surface SspA or SspB polypeptide were then compared for their abilities to adhere to a range of antigen I/II polypeptide substrates. More than twice as many L. lactis cells expressing SspA bound to immobilized salivary agglutinin glycoprotein (SAG) as did L. lactis cells expressing SspB. In contrast, lactococci expressing SspB adhered twice as well as lactococci producing SspA to collagen type I and to Candida albicans. The binding of A. naeslundii to lactococci was only weakly enhanced by surface expression of Ssp polypeptides. L. lactis(pTREX1-sspB) cells bound in greater numbers to SAG than did Enterococcus faecalis JH2-2 cells expressing SspB from pAM401EB-5. The results suggest that SspA and SspB have markedly different binding affinities for their oral substrates and thus may function to promote site diversity in colonization by S. gordonii.

Candida albicans binding to the oral bacterium Streptococcus gordonii involves multiple adhesin-receptor interactions

Candida albicans binds to several species of oral streptococci, in particular Streptococcus gordonii, through recognition of a streptococcal cell wall polysaccharide receptor (A. R. Holmes, P. K. Gopal, and H. F. Jenkinson, Infect. Immun. 63:1827-1834, 1995). We now show that isogenic cell surface protein mutants of S. gordonii DL1, unaltered in expression of cell wall polysaccharide, are reduced in ability to support adherence of C. albicans cells in a solid-phase assay. Inactivation of the S. gordonii cshA and cshB genes, encoding high-molecular-mass cell surface polypeptides, and inactivation of the sspA and sspB genes, encoding antigen I/II salivary adhesins, resulted in 40 and 79% reductions, respectively, in adherence of C. albicans cells. Inactivation of the S. gordonii scaA gene encoding a cell surface lipoprotein had no effect on C. albicans adherence. Polyclonal antiserum to streptococcal antigen I/II protein SpaP and antibodies specific to the amino-terminal nonrepetitive (NR) domain of CshA both inhibited adherence of C. albicans to S. gordonii cells. Conversely antibodies to the amino acid repeat block repetitive (R) domain of CshA, or to ScaA, did not inhibit C. albicans adherence. Immobilized recombinant polypeptide fragments of CshA comprising NR domain or R domain sequences both supported adherence of C. albicans cells. Expression of S. gordonii SspB protein on the surface of Enterococcus faecalis conferred on the enterococcal cells the ability to bind C. albicans, and this was ablated by antigen I/II antiserum. Collectively the results suggest that interaction of C. albicans with S. gordonii is mediated by a complement of adhesin-receptor interactions that involves two families of streptococcal multifunctional polypeptide adhesins, bacterial cell wall polysaccharide, and as yet unidentified yeast cell surface components.

Cell surface polypeptide CshA mediates binding of Streptococcus gordonii to other oral bacteria and to immobilized fibronectin

Isogenic mutants of Streptococcus gordonii DL1 (Challis) in which the genes encoding high-molecular-mass cell surface polypeptides CshA and/or CshB were inactivated were deficient in binding to four strains of Actinomyces naeslundii and two strains of Streptococcus oralis. Lactose-sensitive interactions of S. gordonii with A. naeslundii ATCC 12104 and PK606 were associated with expression of cshA but not of cshB. Lactose-insensitive interactions of S. gordonii with A. naeslundii T14V and WVU627, and with S. oralis C104 and 34, were dependent on expression of cshA and cshB. S. gordonii DL1 cells bound to immobilized human fibronectin (Fn), but not to soluble Fn, in a dose-dependent manner, and binding was noninhibitable by heparin. S. gordonii cshA and cshB mutants were also deficient in binding to immobilized human Fn. Antibodies to an NH2-terminal nonrepetitive region (amino acid residues 42 to 886) of recombinant CshA inhibited binding of S. gordonii DL1 cells to A. naeslundii T14V and PK606 and to immobilized Fn. Conversely, antibodies to an amino acid repeat block segment of the COOH-terminal domain (amino acid residues 2026 to 2508) were not inhibitory to adherence. Assays using CshA-specific antibodies revealed that surface expression of CshA was reduced in cshB mutants. The results suggest that CshA acts as a multifunctional adhesin in S. gordonii and that major adhesion-mediating sequences are specified within the nonrepetitive NH2-terminal region of the polypeptide.

Tandem genes encode cell-surface polypeptides SspA and SspB which mediate adhesion of the oral bacterium Streptococcus gordonii to human and bacterial receptors

The highly conserved antigen I/II family of polypeptides produced by oral streptococci are believed to be colonization determinants and may mediate adhesion of bacterial cells to salivary glycoproteins absorbed to cells and tissues in the human oral cavity. Streptococcus gordonii is shown to express, on the cell surface, two antigen I/II polypeptides designated SspA and SspB (formerly Ssp-5) that are the products of tandemly arranged chromosomal genes. The structure and arrangement of these genes is similar in two independently isolated strains, DL1 and M5, of S. gordonii. The mature polypeptide sequences of M5 SspA (1539 amino acid (aa) residues) and SspB (1462 aa residues) are almost wholly conserved (98% identical) in the C-terminal regions (from residues 796 in SspA and 719 in SspB, to the respective C-termini), well-conserved (84%) at the N-terminal regions (residues 1-429), and divergent (only 27% identical residues) within the intervening central regions. Insertional inactivation of the sspA gene in S. gordonii DL1 resulted in reduced binding of cells to salivary agglutinin glycoprotein (SAG), human erythrocytes, and to the oral bacterium Actinomyces naeslundii. Further reductions in streptococcal cell adhesion to SAG and to two strains of A. naeslundii were observed when both sspA and sspB genes were inactivated. The results suggest that both SspA and SspB polypeptides are involved in adhesion of S. gordonii cells to human and bacterial receptors.

Interactions of Candida albicans with bacteria and salivary molecules in oral biofilms

The yeast Candida albicans coaggregates with a variety of streptococcal species, an interaction that may promote oral colonization by yeast cells. C. albicans and Candida tropicalis are the yeasts most frequently isolated from the human oral cavity and our data demonstrate that both these species bind to Streptococcus gordonii NCTC 7869 while two other Candida species (Candida krusei and Candida kefyr) do not. Adherence of C. albicans was greatest when the yeast had been grown at 30 degrees C to mid-exponential growth phase. For 21 strains of C. albicans there was a positive correlation between the ability to adhere to S. gordonii and adherence to experimental salivary pellicle. Whole saliva either stimulated or slightly inhibited adherence of C. albicans to S. gordonii depending on the streptococcal growth conditions. The results suggest that the major salivary adhesins and coaggregation adhesins of C. albicans are co-expressed.

Adherence of Candida albicans to a cell surface polysaccharide receptor on Streptococcus gordonii

Candida albicans ATCC 10261 and CA2 bound to cells of the oral bacteria Streptococcus gordonii, Streptococcus oralis, and Streptococcus sanguis when these bacteria were immobilized onto microtiter plate wells, but they did not bind to cells of Streptococcus mutans or Streptococcus salivarius. Cell wall polysaccharide was extracted with alkali from S. gordonii NCTC 7869, the streptococcal species to which C. albicans bound with highest affinity, and was effective in blocking the coaggregation of C. albicans and S. gordonii cells in the fluid phase. When fixed to microtiter plate wells, the S. gordonii polysaccharide was bound by all strains of C. albicans tested. The polysaccharide contained Rha, Glc, GalNAc, GlcNAc, and Gal and was related compositionally to previously characterized cell wall polysaccharides from strains of S. oralis and S. sanguis. The adherence of yeast cells to the immobilized polysaccharide was not inhibitable by a number of saccharides. Antiserum raised to the S. gordonii NCTC 7869 polysaccharide blocked adherence of C. albicans ATCC 10261 to the polysaccharide. The results identify a complex cell wall polysaccharide of S. gordonii as the coaggregation receptor for C. albicans. Adherent interactions of yeast cells with streptococci and other bacteria may be important for colonization of both hard and soft oral surfaces by C. albicans.

Oral Candida: clearance, colonization, or candidiasis?

Candida albicans is frequently isolated from the human mouth, yet few carriers develop clinical signs of candidiasis. Oral candidiasis presents clinically in many forms. This reflects the ability of the yeast to colonize different oral surfaces and the variety of factors which predispose the host to Candida colonization and subsequent infection. Colonization of the oral cavity appears to be facilitated by several specific adherence interactions between C. albicans and oral surfaces which enable the yeast to resist host clearance mechanisms. Thus, Candida has been shown to adhere to complement receptors, various extracellular matrix proteins, and specific sugar residues displayed on host or bacterial surfaces in the oral cavity. Oral candidiasis results from yeast overgrowth and penetration of the oral tissues when the host's physical and immunological defenses have been undermined. Tissue invasion may be assisted by secreted hydrolytic enzymes, hyphal formation, and contact sensing. While these and other phenotypic characteristics may endow certain Candida species or strains with a competitive advantage in the oral cavity, it is the host's immune competence that ultimately determines whether clearance, colonization, or candidiasis occurs.

Detection of Candida albicans and other yeasts in blood by PCR

Primers complementary to the region of genes coding for rRNA in Candida albicans were used in PCRs to detect yeast DNA extracted from blood samples containing various Candida species. One fragment (105 bp) was amplified from all yeasts tested, whereas a second (684 bp) was only amplified when C. albicans DNA was present. The level of sensitivity was 15 +/- 5 (mean +/- standard error) CFU of C. albicans per ml of blood.

Yeast-specific DNA probes and their application for the detection of Candida albicans

Two DNA fragments cloned from the genome of Candida albicans ATCC 10261 may be useful in the rapid diagnosis of disseminated candidosis. One sequence (probe EOB1) was specific for C. albicans (positive hybridisation with 45 strains tested). The second sequence (probe EOB2) detected C. albicans, as well as five other pathogenic Candida spp. and Saccharomyces cerevisiae, but did not react with human or bacterial DNA. Both probes were repetitive sequences in the genome of C. albicans. Probe EOB1 was used to detect, without DNA amplification, 500 C. albicans yeast cells in 1 ml of human blood.

Mechanisms of aggregation accompanying morphogenesis in Candida albicans

Cultures of Candida albicans yeast cells do not normally aggregate, but extensive aggregation accompanies the induction of mycelial growth, indicating the occurrence of cell surface changes during the yeast to mycelial transition. Aggregation correlated with the formation of germ tubes as did changes in surface charge determined by attachment to ion exchange sepharose beads. Yeast cells of all strains examined were negatively charged and attachment to positively charged (DEAE) sepharose beads increased following germ tube formation. If Mg2+ was present during germ tube formation, a high degree of clumping occurred that could only be dispersed by treatment with protein-disrupting agents. Trypsin, chymotrypsin, SDS, urea, guanidine HCl and dithiothreitol but not EDTA or EGTA caused irreversible dispersal of aggregates, although germ tube aggregates dispersed by treatment with buffers at high pH reaggregated if neutralized or if calcium ions were added. Germ tube cultures produced in divalent cation-deprived medium formed aggregates that were readily dispersed by washing. However, the addition of Mg2+ or other divalent cations (Ca2+, Zn2+, Cu2+, Fe2+) caused immediate aggregation of these cultures. These results suggest that divalent cation crossbridging between opposing anionic sites and protein interactions act synergistically to promote aggregation of C. albicans germ tube cells.

Peanut sensitivity as a cause of burning mouth

A patient with a history of a burning tongue together with discomfort of the labial and buccal mucosae was given an elimination diet and skin patch tests to determine the allergen in her diet. The patient was identified as being intolerant of an aqueous peanut extract. Three allergens in peanut butter were identified, the one with greatest reactivity being a heat-stable, water-soluble, nonglycosylated protein with a molecular weight in excess of 10 kD. Modification of her diet has resulted in resolution of the oral problem.

Ammonium assimilation by Candida albicans and other yeasts: a 13N isotope study

Nuclear magnetic resonance spectra of cultures of Candida albicans incubated in the presence of 15N-labelled ammonium demonstrated that glutamine and glutamate were the only initial products of ammonium assimilation. The nature of the route of assimilation in the yeasts Candida albicans, Saccharomyces cerevisiae, and Candida tropicalis was further examined by the use of the short-lived isotope 13N. [13N]ammonium was generated in the reaction 16O(p,alpha)13N, induced by proton bombardment of water in tandem accelerator. High-pressure liquid chromatography was used to separate and identify the products of assimilation, and radioactivity was detected and corrected for decay, using a computer-linked NaI scintillation detector. In the three yeasts studied, the labelled ammonium was assimilated into the acid-extractable fraction of cell suspensions within 1 min, and over 75% was converted to glutamine and glutamate. Subsequent to exhaustion of the labelled ammonium, the stoichiometry of the distribution of radiolabel was consistent with a net transfer of radiolabel from glutamine to glutamate, confirming the operation of glutamate synthase (EC 1.4.1.14) in these yeasts. Initial assimilation of label was mostly into glutamine (at a maximal rate within 10 s in C. albicans), whereas accumulation in glutamate did not occur at maximal rate until more than 70% of the labelled ammonium had been assimilated (between 30 and 60 s in C. albicans). We conclude that the glutamine synthetase-glutamate synthase pathway is the major route of ammonium assimilation in C. albicans and also in nitrogen-starved cultures of S. cerevisiae and C. tropicalis.

Effect of calcium ion uptake on Candida albicans morphology

In liquid culture using a synthetic medium, added magnesium but not calcium was required for exponential growth of Candida albicans yeast cells. However, medium without added divalent cations supported 2-3 generations of yeast growth or germ tube induction. The addition of calcium ions (1.0 mM) at any stage during the induction of germ tube formation caused reversion to a yeast mode of growth, in contrast to the effect of zinc and cobalt ions which were toxic to all growth. Inhibition of germ tube formation by calcium was not observed in the presence of either magnesium (10 microM) or manganese (100 microM). The presence of either of these ions caused inhibition of 45Ca uptake in yeast cultures. We conclude that unrestricted calcium uptake resulted in the specific inhibition of C. albicans mycelial growth, indicating a critical role for calcium in the regulation of C. albicans morphogenesis.

Ammonium assimilation by Candida albicans and other yeasts: evidence for activity of glutamate synthase

Activities and properties of the ammonium assimilation enzymes NADP+-dependent glutamate dehydrogenase (GDH), glutamate synthase (GOGAT) and glutamine synthetase (GS) were determined in batch and continuous cultures of Candida albicans. NADP+-dependent GDH activity showed allosteric kinetics, with an S0.5 for 2-oxoglutarate of 7.5 mM and an apparent Km for ammonium of 5.0 mM. GOGAT activity was affected by the buffer used for extraction and assay, but in phosphate buffer, kinetics were hyperbolic, yielding Km values for glutamine of 750 microM and for 2-oxoglutarate of 65 microM. The enzymes GOGAT and NADP+-dependent GDH were also assayed in batch cultures of Saccharomyces cerevisiae and three other pathogenic Candida spp.: Candida tropicalis, Candida pseudotropicalis and Candida parapsilosis. Evidence is presented that GS/GOGAT is a major pathway for ammonium assimilation in Candida albicans and that this pathway is also significant in other Candida species.

Nutritional factors determine germ tube formation in Candida albicans

Following a short (3 h) period of carbon starvation, exponential phase yeast cells of Candida albicans rapidly (T50 45 min) formed germ tubes in a glucose/ammonium ion solution. The presence of both a sugar (glucose, sucrose or galactose) and a nitrogen source (ammonium ion or an amino acid metabolized via glutamate) was critical for morphogenesis.

Proline-induced germ-tube formation in Candida albicans: role of proline uptake and nitrogen metabolism

Proline-induced germ-tube formation and cell-cell aggregation in four strains of Candida albicans were completely inhibited when the pH of the medium was 5.0 or lower, whereas morphogenesis induced by N-acetylglucosamine (GlcNAc) was unaffected even at pH 4.5. The pH sensitivity of proline-induced germ-tube formation was not caused by a modulation of proline uptake, which was unchanged over the pH range 4.5-6.5. The proline uptake system was specific, constitutive and subject to ammonium repression, and only one permease was detected, with a Km of 179 microM. Cultures deprived of nitrogen in the presence of glucose were derepressed for proline uptake but the yeast-mycelial transition could not be mediated by either proline or GlcNAc. The inhibition of morphogenesis was reversed when the nitrogen starvation was relieved by the addition of ammonium ions, proline, or certain amino acids. These results indicate that the nitrogen status of the cells is critical for the morphogenesis of C. albicans.

Factors affecting the interferon sensitivity of human cytomegalovirus

Several factors affected the interferon sensitivity of human cytomegalovirus in human foreskin fibroblast cultures. An inoculum of infected cells was up to 300-fold less sensitive than a cell-free inoculum of equivalent input multiplicity. A 10-fold increase in the dose of infectious units of either type of inoculum was associated with a 10-fold or greater decrease in interferon sensitivity. Several aspects of the virus-cell interaction were examined and parameters indicative of cell infection were less inhibited by interferon than were those for virus replication.

Multiplicity-dependent replication of varicella-zoster virus in interferon-treated cells

The inhibitory effects of interferon (IF) on the replication of varicella-zoster (VZ) virus in human foreskin fibroblast (HFF) cultures inoculated with infected cells or with cell-free virus were assayed by measuring (1) yields of infected cells, (2) plaques, (3) microfoci and (4) cytopathic effects. More IF was needed to reduce yields of infected cells at high input multiplicities of challenge than at low input multiplicites, and still more IF was needed to prevent cytopathology due to VZ virus. A cell-free virus inoculum was more sensitive to the inhibitory effects of IF than an inoculum of infected cells. With the latter, but not with cell-free virus, the continuous presence of IF in the medium was necessary for it to express its maximum antiviral activity. To explain these results, it is suggested that some herpesviruses may establish "reservoirs' of infectivity and thus provide a prolonged challenge to IF-treated cells which are not uniformly resistant to infection.