Evolution of inflammatory response and cellular immune responses in a murine model of disseminated blastomycosis

Murine models of blastomycosis, coccidioidomycosis, and histoplasmosis

Animal models have contributed much to the knowledge of fungal infections and their corresponding therapeutic treatments. This is true for animal models of the primary fungal pathogens, Blastomyces dermatitidis, Coccidioides immitis, and Histoplasma capsulatum. This review gives a brief background of human diseases associated with these organisms and describes the development, details, and utility of murine models of blastomycosis, as well as coccidioidomycosis and histoplasmosis.

Genomic cloning, characterization, and functional analysis of the major surface adhesin WI-1 on Blastomyces dermatitidis yeasts

WI-1 is a 120-kDa surface protein adhesin on Blastomyces dermatitidis yeasts that binds CD18 and CD14 receptors on human macrophages. We isolated and analyzed a clone of genomic WI-1 to characterize this key adherence mechanism of the yeast. The 9.3-kilobase insert contains an open reading frame of 3438 nucleotides and no introns. The amino acid sequence of native WI-1 matches the deduced sequence of genomic WI-1 at positions 757-769, 901-913, and 1119-1138, demonstrating the cloned gene is authentic WI-1. The complete coding sequence has 30 highly conserved repeats of 24 amino acids arrayed in tandem in two noncontiguous regions of the protein. The repeat sequence is homologous to the Yersiniae adhesin invasin, the C terminus displays an epidermal growth factor-like domain, and the N terminus has a short hydrophobic sequence that may be a membrane-spanning domain. The tandem repeats are predicted to be at the exposed surface of the protein, thereby explaining the adhesive properties of WI-1. The WI-1 promoter contains a CAAT box (nucleotide positions 2287-2290), TATA box (2380-2385), and CT motif (2399-2508). Transcription is initiated within the CT motif at nucleotide 2431. A 5.5-kilobase subclone containing the full coding sequence of WI-1 was expressed as a histidine-tagged fusion protein in Escherichia coli. Recombinant WI-1 has the expected molecular mass of 120 kDa, is strongly recognized in Western blots by rabbit anti-WI-1 antiserum, and binds human macrophage receptors in the same manner as native WI-1. This work clarifies a key adherence mechanism of B. dermatitidis and will permit further analysis of WI-1-mediated attachment to host cells, receptors, and extracellular matrix.

Correlative studies of blastogenic responses and interleukin 1 production by mononuclear cells from patients with zoopathogenic fungal infections

The production of interleukin 1 (IL 1) by adherent peripheral blood mononuclear cells (PBMC) was quantitated in 16 individuals infected with Histoplasma capsulatum or Blastomyces dermatitidis and 16 age-matched controls. In parallel, we measured blastogenic responses to phytohemagglutinin (PHA) by PBMC from patients and controls. Of the 16 patients, six had pulmonary histoplasmosis, six had disseminated histoplasmosis, two had pulmonary blastomycosis, and two had disseminated blastomycosis. At the time of study, none of the patients were receiving immunosuppressive agents or had an underlying debilitating illness. Proliferative responses by PBMC from patients to PHA were significantly (P less than 0.05) less than the mean response by PBMC from an equal number of controls. In the 16 controls, the increase in secretion of IL 1 by lipopolysaccharide (LPS)-stimulated adherent cells over unstimulated cells ranged from 18 to 40 units of IL 1 activity per 10(5) adherent cells. The increment in IL 1 levels between LPS-stimulated adherent PBMC and unstimulated cells was diminished (less than 18 units of IL 1 activity per 10(5) adherent cells) in five of the 16 patients. Diminished IL 1 secretion in response to LPS was associated with impaired PHA responses in four of 10 patients.

Fungal-strain-dependent alterations in the time course and mortality of chronic murine pulmonary blastomycosis

Intratracheal injection of 10(4) conidia of Blastomyces dermatitidis strain M1-A into mice was shown in previous work to induce chronic pulmonary and disseminated infection with histopathologic features of chronic human blastomycosis. Furthermore, 10-fold variations in inoculum density produced marked changes in mean survival times (MSTs), i.e., 32 days at 10(6), 36 days at 10(5), 97 days at 10(4), and 172 days at 10(3). A second strain (M1-B) failed to induce death in this model. To assess fungal-strain-dependent virulence, we extended these previous studies to 11 additional human isolates. Groups of male BALB/cByJ mice (6 to 8 weeks old) were injected intratracheally with 10(4) conidia from each of the 13 strains; the mice were weighed weekly and monitored for mortality, and their lungs were examined histopathologically. Infection rate and mortality were 100% in all groups except for the M1-B inoculated mice. For strains M1-B and M1-A, MST and mortality curves were not significantly different from those observed in our previously reported experiments. Four different survival patterns were noted in infected mice. The shortest MSTs were produced by strains M2-E, M2-B, M2-K, M2-H, and M2-A (24, 26, 26, 27, and 31 days, respectively), and the longest MST was seen in animal groups inoculated with strains M2-J and M2-G (130 and 134 days, respectively). Strains M2-I, M2-F, and M2-D produced intermediate MSTs of 65, 79, and 80 days, respectively. The 107-day MST induced by M1-A did not differ from strain M2-C-induced MST but differed significantly from the MST produced by the other strains. Pulmonary histopathology was similar in all animals dying with blastomycosis. The wide spectrum in survival times was not related to differences in clinical status of the patient from whom the isolate had been obtained, to fungal inoculum viability, or to individual mouse weight at inoculation. Strain-dependent virulence factors present in these fungal isolates alter the disease course in inbred mice in a fashion similar to that induced by 10-fold inoculum variation of strain M1-A conidia. These 13 isolates of B. dermatitidis, 1 avirulent and 12 with differing levels of virulence, provide tools for future studies into the nature of fungal virulence determinants in chronic blastomycosis.