Experimental induction of anergy to coccidioidin by antigens of Coccidioides immitis

Early Events in Coccidioidomycosis

Since its description nearly 130 years ago, hundreds of studies have deepened our understanding of coccidioidomycosis, also known as valley fever (VF), and provided useful diagnostic tests and treatments for the disease caused by the dimorphic fungi Coccidioides spp. In general, most of the literature has addressed well-established infections and has described patients who have experienced major complications. In contrast, little attention has been given to the earliest consequences of the pathogen-host interaction and its implications for disease manifestation, progression, and resolution. The purpose of this review is to highlight published studies on early coccidioidomycosis, identify gaps in our knowledge, and suggest new or former research areas that might be or remain fertile ground for insight into the early stages of this invasive fungal disease.

Valley fever: danger lurking in a dust cloud

Coccidioides immitis and Coccidioides posadasii contribute to the development of Valley Fever. The ability of these fungal pathogens to evade the host immune system creates difficulty in recognition and treatment of this debilitating infection. In this review, we describe the current knowledge of Valley Fever and approaches to improve prevention, detection, and treatment.

Cytokine involvement in immunomodulatory activity affected by Candida albicans mannan

Candida albicans mannoprotein (MAN) administered intravenously to mice stimulates the production of splenic CD8+ effector cells which downregulate delayed hypersensitivity (DH) in immunized mice. Cytokine involvement in the induction and/or elicitation of downregulation was studied by (i) examining murine splenocytes qualitatively for mRNA for interleukin-2 (IL-2), IL-4, IL-10, IL-12p40, and gamma interferon (IFN-gamma), (ii) quantitating splenocyte mRNA for IL-12p40 by quantitative-competitive reverse transcriptase-mediated PCR, and (iii) measuring serum levels of IL-12p40 and IL-12p70 by capture enzyme-linked immunosorbent assay, each performed at selected intervals over 96 h after giving MAN. Further, the effect of in vivo administration of anti-IL-4 on the induction and elicitation of MAN-specific DH in MAN-treated mice was measured. Expression of IL-12p40 mRNA in the spleen was reduced to near 0 during the first 24 h but rebounded thereafter. Transcripts for IL-10 were present throughout the 96-h period, whereas those for IL-4 and IFN-gamma were either weak or undetectable prior to 24 to 48 h. In vivo administration of anti-IL-4 partially abrogated the downregulatory effect of MAN only when given at the time of MAN administration. Serum levels of IL-12p40, but not IL-12p70, were increased by 24 h and maximal at 48 h. The antagonistic effect of IL-12p40 could contribute to the mechanism(s) for downregulation of DH. Moreover, IL-10, IL-4, and/or IFN-gamma, interacting with MAN-activated cells in the absence of biologically active IL-12, may induce the production of CD8+ downregulatory effector cells. Partial abrogation of downregulatory activity in animals treated with anti-IL-4 at the time of induction of such activity lends support to this hypothesis.

Characterization of a soluble protein of Coccidiodes immitis with activity as an immunodiffusion-complement fixation antigen

A 48-kilodalton (kDa) electrophoretically distinct antigen from Coccidioides immitis mycelial- and spherule-endospore-phase filtrates was previously associated by immunoblotting with the immunodiffusion band that corresponds to complement-fixing activity (ID-CF). To characterize this antigen and its precursor, both mycelial- and spherule-endospore-phase filtrates were fractionated by size exclusion chromatography, lectin affinity chromatography, and nondenaturing electrophoresis. By size exclusion chromatography, most of the protein and carbohydrate of the crude filtrates eluted in a peak of average molecular size less than 30 kDa, although other components were detected. ID-CF activity was associated with the component at a relative mobility of 110 kDa. Fractions containing the ID band that corresponded to tube precipitin activity occurred from 200 to 40 kDa. The appearance of the 48-kDa band in denaturing sodium dodecyl sulfate-polyacrylamide gel electrophoresis (PAGE) specifically coincided with the fractions containing ID-CF activity. Nondenaturing PAGE of filtrates showed silver-stainable and immunoblot-reactive bands in the region of 110 kDa. Prior treatment with pronase destroyed this electrophoretically separable antigen, whereas periodate had no effect. Trypsin did not affect the 110-kDa band in unheated or unreduced antigen. Mycelial filtrates were chromatographed on lentil lectin or concanavalin A-Sepharose 4B to deplete them of glucose- or mannose-containing carbohydrate. The effluent fraction contained ID-CF activity and, upon denaturing electrophoresis, the 48-kDa antigen. The 110-kDa protein represents the ID-CF antigen which is heat labile and denatured to a 48-kDa band by sodium dodecyl sulfate-PAGE.

Extraction of serologic and delayed hypersensitivity antigens from spherules of Coccidioides immitis

We have used an aqueous toluene extraction procedure to obtain antigens from mature spherules of Coccidioides immitis. This extract contained many antigens as determined by immunoblotting and two-dimensional immunoelectrophoretic studies. These included antigens with specificity for tube precipitin-type antibodies having molecular weights greater than or equal to 100 KDa. The extract also displayed lymphocyte-transforming activity when tested on human peripheral blood mononuclear leukocytes from donors who react to coccidioidal skin tests but elicited no such stimulation of cells from persons whose coccidioidal skin tests were nonreactive. At high concentrations of the extract, lymphocyte transformation did not occur, a finding that could not be explained by nonspecific toxicity. When gel filtration was employed to separate antigens by size, tube precipitin-like activity and specific coccidioidal delayed-type hypersensitivity displayed overlap, although only the latter activity was apparent in lower molecular weight pools.

Suppression of T-lymphocyte response by Coccidioides immitis antigen

Intravenous injection of BALB/c mice with coccidioidin or an alkali-soluble cell wall extract of Coccidioides immitis mycelia resulted in the induction of a splenic cell population(s) that suppressed delayed-type hypersensitivity response to coccidioidal antigen. To determine whether the levels of C. immitis antigen produced during the course of active coccidioidal disease might also cause suppression of T-lymphocyte response, BALB/c mice were infected by intranasal instillation of arthroconidia, and 2 weeks later, their sera were evaluated for suppression of T-lymphocyte response in syngeneic recipients. Intravenous transfer of sera, which were shown to contain high levels of coccidioidal antigen by an enzyme-linked immunoadsorbent assay, suppressed the delayed-type hypersensitivity response of recipients to immunization with coccidioidin. Solid-phase immunoadsorption of the sera with goat antibodies to C. immitis antigens removed the suppressive component(s). To determine whether the suppressive effect of circulating coccidioidal antigen(s) was associated with the activation of a splenic suppressor cell(s), as was observed in mice injected intravenously with coccidioidal antigen, spleen cell lysates were prepared from infected donors, and after filtration to remove viable fungi, the lysates were transferred to syngeneic mice. Recipients of lysates from infected but not noninfected donors were suppressed in their response to immunization with coccidioidin. Collectively, these results provide evidence that depressed T-cell responses observed in coccidioidomycosis are associated with, and may be attributable to, the activation of a suppressor cell or factor by circulating C. immitis antigens.

Serum-mediated suppression of lymphocyte transformation responses in coccidioidomycosis

Lymphocyte transformation (LT) responses to coccidioidin (CDN) and spherulin were suppressed in 11 (73%) of 15 patients with active coccidioidomycosis when their mononuclear cells were assayed in autologous serum as compared to serum from healthy, CDN skin test-positive subjects. Suppressed LT responses were specific for Coccidioides immitis antigens in 7 (64%) of the 11 patients. Immunoaffinity chromatography of patient sera with Staphylococcus protein A adsorbed the suppressor component(s) and thereby established that suppression was attributed to immunoglobulin G, either alone or complexed with antigen. The possibility that suppression was mediated by immune complexes was examined by adding complexes formed in vivo or in vitro to mononuclear cell cultures of healthy CDN-reactive persons before LT assays. Although complexes prepared in this manner were reactive in an enzyme-linked immunosorbent assay designed to detect Coccidioides antigen-specific immune complexes, no suppression of LT responses was observed. We conclude that serum-mediated suppression of LT responses in coccidioidomycosis is attributed to monomeric and not immune-complexed immunoglobulin G antibody.

Course of coccidioidomycosis in intratracheally infected guinea pigs

Two hundred Hartley-inbred guinea pigs were infected intratracheally with 50 viable arthrospores of Coccidioides immitis. At weeks 1 through 10 postinfection, groups of 20 guinea pigs were assayed for skin test, macrophage migration inhibitory factor (MIF), and lymphocyte transformation (LT) responses to coccidioidin. Forty-eight hours after skin testing and just before MIF and LT assays, blood was obtained for complement-fixing (CF) antibody titers and the animals were autopsied to assess the extent of fungal dissemination. Immunological assays established that skin tests and MIF responses converted within 3 weeks of infection. LT responses were not demonstrable until week 5. Dissemination of C. immitis to the liver or spleen was an early event, with 21% of guinea pigs positive by week 2 and 70% positive by week 5. CF antibody titers were demonstrable at week 5, increased logarithmically through week 7, then increased at a slower rate thereafter. Concomitant with the decreased rate of antibody production, guinea pigs began to clear C. immitis from their extrapulmonary tissues. Skin test responses peaked at 6 weeks postinfection when CF antibody titers were less than or equal to 1:16 and then plateaued with increased CF titers. Although this overall immunological profile is consistent with the disease in humans, there was not a direct correlation between CF antibody titer and dissemination to the liver or spleen, nor was there an inverse correlation between CF antibody titers and skin test or MIF responses. Rather, CF antibody titers and cell-mediated immune responses were equally demonstrable in guinea pigs with disseminated or nondisseminated disease.

Extraction of skin test activity from Coccidioides immitis mycelia by water, perchloric acid, and aqueous phenol extraction

Water, perchloric acid extracts, and fractions of partially defatted whole mycelia of Coccidioides immitis contained delayed skin test activity when tested in C. immitis-infected guinea pits. Aqueous phenol extraction of these fractions resulted in partitioning of activity between aqueous-soluble and phenol-soluble fractions; activity was found to be water soluble after removal of phenol by extensive dialysis. Highest specific activity skin test antigen was invariably found in the phenol-soluble phase, water-soluble fraction. Material of equivalent activity could also be extracted directly from the defatted mycelia. Skin test active fractions contained glucose, mannose, 3-O-methylmannose, glucosamine, and amino acids.