Occurrence of antigenic (species-specific?) partially 3-O-methylated heteromannans in cell wall and soluble cellular (nonwall) components of Coccidioides immitis mycelia

Abstract

Skin test-active, phenol-soluble, water-soluble (PSWS) extracts of Coccidioides immitis whole, defatted mycelia were compared with skin test-active, alkalisoluble, water-soluble (ASWS) extracts of mycelial cell walls. Both PSWS and ASWS extracts contained partially 3-0-methylated mannan. Composition analysis of both PSWS and ASWS extracts indicated mannose and glucose as major components, whereas 3-0-methylmannose and galactose were minor constituents. These heteromannans and glucans could be obtained from cell walls by extraction with either mild acid or alkali, but not with aqueous phenol. We therefore conclude that the PSWS extracts which were obtainable from whole mycelia but not from cell walls represent cellular (i.e., periplasmic, membrane associated, or cytoplasmic), nonwall polymers. Both PSWS and ASWS mycelial extracts and their gel filtration fractions reacted with rabbit antispherule serum, but with little cross-reactivity. However, alkali treatment of higher-molecularweight PSWS extract polymers yielded products that cross-reacted with serological identity with low-molecular-weight components of ASWS extracts of mycelial walls, indicating that cell walls and cellular polymers share antigenic determinants. Finally, gel filtration of PSWS extracts on Sephacryl S-200 and Sepharose CL 4B yielded fractions that reacted with serological identity with one or more components of mycelial cytosol, mycelial culture filtrate and autolysate coccidioidins, and spherulin.

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

“…The monosaccharides were detected as trimethylsilyl methylglycosides of neutral sugars and identified by comparison with authenticated, spectroscopic-grade sugar standards (Aldrich Chemical Co., Inc., Milwaukee, Wis.). The 3-0-MM standard was synthesized by one of the authors as previously described (31,37).…”

“…Previous investigations have demonstrated that methylated mannose-containing polysaccharides occur in the walls of arthroconidia, spherules, and hyphae of C. immitis (3,31,(35)(36)(37). In addition, previous reports have indicated that the ID-TP antigen is predominantly polysaccharide (13, 17, 41), and partial to total loss of reactivity with IgM precipitin occurs when the antigen is subjected to periodate oxidation (13).…”

“…The potential application of synthesized 3-0-MM sug- gested from these results is to use the modified sugar in a diagnostic ELISA for detection of anti-Coccidioides IgM precipitin antibody. The rationale for this proposed application is based on evidence that 3-0-MM is unique to C. immitis among the systemic fungal pathogens (3,37). We previously reported that 3-0-MM was not detected by GC-MS in cell wall preparations of several commonly encountered fungal pathogens, including Blastomyces dermatitidis, Aspergillus fumigatus, Histoplasma capsulatum, and Candida albicans (3).…”

“…To our knowledge, 3-0-MM has so far been found only in Malbranchea spp. and C. immitis among the fungi (3,9,37). have reported that the ID-TP antigen of C. immitis is common to certain related, arthroconidium-forming, gymnoascaceous saprophytes such as Arachniotus, Auxarthron, and Malbranchea spp.…”

“…We also show that reactivity of the antigen with serum samples from patients with coccidioidomycosis is retained after pronase digestion or heating (100°C, 5 min) but is lost after periodate oxidation. Examination of the carbohydrate composition of the TP antibody-reactive antigen (TP-Ag) by gas chromatography-mass spectroscopy revealed 3-0-methylmannose (3-0-MM), a sugar that was previously shown to be a component of immunoreactive fractions of C. immitis (3,15,17,28,(35)(36)(37) and possibly unique to this pathogen among the systemic fungal pathogens (3,37). In this report, we also further examine the serologic reactivity of the 120-kDa TP-Ag and, in particular, the significance of 3-0-MM in precipitin binding to this macromolecule.…”