In vitro lymphocyte responses of coccidioidin skin test-positive and -negative persons to coccidioidin, spherulin, and a coccidioides cell wall antigen

Coccidioides Species: A Review of Basic Research: 2022

Coccidioides immitis and posadasii are closely related fungal species that cause coccidioidomycosis. These dimorphic organisms cause disease in immunocompetent as well as immunocompromised individuals and as much as 40% of the population is infected in the endemic area. Although most infections resolve spontaneously, the infection can be prolonged and, in some instances, fatal. Coccidioides has been studied for more than 100 years and many aspects of the organism and the disease it causes have been investigated. There are over 500 manuscripts concerning Coccidioides (excluding clinical articles) referenced in PubMed over the past 50 years, so there is a large body of evidence to review. We reviewed the most accurate and informative basic research studies of these fungi including some seminal older studies as well as an extensive review of current research. This is an attempt to gather the most important basic research studies about this fungus into one publication. To focus this review, we will discuss the mycology of the organism exclusively rather than the studies of the host response or clinical studies. We hope that this review will be a useful resource to those interested in Coccidioides and coccidioidomycosis.

The clinical laboratory evolution in coccidioidomycosis detection: Future perspectives

Coccidioidomycosis is a systemic disease caused by the fungi Coccidioides immitis and C. posadasii. It is a prevalent disease in arid regions with high temperatures and low precipitations in America. Coccidioidomycosis is a highly endemic disease of US-Mexico border states but commonly underdiagnosed. The diagnosis of coccidiomycosis is not easy due to the lack of specific symptoms; it is usually an integral approach, including clinical laboratory tests as an essential part of the diagnosis. Nevertheless, despite various laboratory tests available, affordability can be a limitation, mainly in developing countries. This review's objectives are 1) to learn the different laboratory approaches that arose and their application for clinical diagnosis; 2) to discuss their advantages and weaknesses, and finally, 3) propose what is on the horizon for future advances in clinical laboratory diagnosis of coccidioidomycosis. It has been a long way in laboratory tests evolution to detect coccidioidomycosis from tissue microscopy to Real-Time PCR. However, there is a delay in technology adoption for Coccidioides spp. detection in the clinical laboratory. The molecular Point of Care Testing (POCT) technology has reached us in our trench while research in PCR variants stills on-going. None of the currently existing scientific literature in coccidioidomycosis research has mentioned it. However, this trend in infectious and non-infectious disease diagnosis will continue in that way in order to offer better options for an easy and fast diagnosis. Undoubtedly, the implementation of molecular POCT for Coccidioides spp. would save resources in health care attention and improve access to diagnostic tools.

Coccidioidomycosis: host response and vaccine development

Coccidioidomycosis is caused by the dimorphic fungi in the genus Coccidioides. These fungi live as mycelia in the soil of desert areas of the American Southwest, and when the infectious spores, the arthroconidia, are inhaled, they convert into the parasitic spherule/endospore phase. Most infections are mild, but these organisms are frank pathogens and can cause severe lethal disease in fully immunocompetent individuals. While there is increased risk of disseminated disease in certain racial groups and immunocompromised persons, the fact that there are hosts who contain the initial infection and exhibit long-term immunity to reinfection supports the hypothesis that a vaccine against these pathogens is feasible. Multiple studies have shown that protective immunity against primary disease is associated with T-helper 1 (Th-1)-associated immune responses. The single best vaccine in animal models, formalin-killed spherules (FKS), was tested in a human trial but was not found to be significantly protective. This result has prompted studies to better define immunodominant Coccidioides antigen with the thought that a subunit vaccine would be protective. These efforts have defined multiple candidates, but the single best individual immunogen is the protein termed antigen 2/proline-rich antigen (Ag2/PRA). Studies in multiple laboratories have shown that Ag2/PRA as both protein and genetic vaccines provides significant protection against mice challenged systemically with Coccidioides. Unfortunately, compared to the FKS vaccine, it is significantly less protective as measured by both assays of reduction in fungal CFU and assays of survival. The capacity of Ag2/PRA to induce only partial protection was emphasized when animals were challenged intranasally. Thus, there is a need to define new candidates to create a multivalent vaccine to increase the effectiveness of Ag2/PRA. Efforts of genomic screening using expression library immunization or bioinformatic approaches to identify new candidates have revealed at least two new protective proteins, expression library immunization antigen 1 (ELI-Ag1) and a beta-1,3-glucanosyltransferase (GEL-1). In addition, previously discovered antigens such as Coccidioides-specific antigen (CSA) should be evaluated in assays of protection. While studies have yet to be completed with combinations of the current candidates, the hypothesis is that with increased numbers of candidates in a multivalent vaccine, there will be increased protection. As the genome sequences of the two Coccidioides strains which are under way are completed and annotated, the effort to find new candidates can increase to provide a complete genomic scan for immunodominant proteins. Thus, much progress has been made in the discovery of subunit vaccine candidates against Coccidioides and there are several candidates showing modest levels of protection, but for complete protection against pulmonary challenge we need to continue the search for additional candidates.

In vitro whole-blood analysis of cellular immunity in patients with active coccidioidomycosis by using the antigen preparation T27K

Measurement of cellular immunity in human coccidioidomycosis has important diagnostic and prognostic implications. The coccidioidin skin test has been the standard for the measurement of this, but it is not available in the United States. We examined the utility of measuring surface expression of CD69 on T lymphocytes in whole blood incubated with the coccidioidal antigen preparation T27K as an alternative to the skin test. Seventy donors with active coccidioidomycosis were studied. The mean fluorescent intensity (MFI) of CD69 expression on CD3 lymphocytes in response to T27K was 28.61 +/- 1.77, significantly greater than the control response of 11.45 +/- 0.78 (P < 0.001). The MFI CD69 response to T27K above that for the control (MFI CD69 above control) was 6.35 +/- 2.18 for seven subjects with disseminated coccidioidomycosis who were studied within 5 months of diagnosis. This was significantly below the value of 20.17 +/- 3.17 for 18 subjects with pulmonary coccidioidomycosis studied within 5 months of diagnosis and the value of 19.58 +/- 2.91 for 27 subjects with disseminated coccidioidomycosis studied after 5 months of diagnosis (for both, P < 0.05). There was an inverse correlation between coccidioidal clinical score and MFI CD69 above control for all 34 subjects with disseminated coccidioidomycosis (r = 0.362; P = 0.036) but not for the 36 subjects with pulmonary disease (r < 0.001; P = 0.993). Among 30 subjects for whom data were available, there was a highly significant association between the MFI CD69 above control and the supernatant concentrations of gamma interferon, interleukin-2 (IL-2), and tumor necrosis factor alpha (for all, P < 0.001), but not for IL-4, IL-5, or IL-10. These data indicate that in vitro assessment of CD69 expression on T lymphocytes by using T27K may be a useful measure of cellular immune response among subjects with active coccidioidomycosis.

Reversal of coccidioidal anergy in vitro by dendritic cells from patients with disseminated coccidioidomycosis

Coccidioides immitis is a pathogenic, dimorphic fungus found in the southwestern United States and is the causative agent of coccidioidomycosis. Extrathoracic dissemination of coccidioidomycosis is associated with a lack of cellular immunity. Dendritic cells (DCs) have been shown to initiate and modulate cellular immune responses. To determine whether DCs could modulate or initiate the immune response in this disease, monocyte-derived DCs were generated from coccidioidal Ag nonresponsive patients with disseminated coccidioidomycosis and healthy nonimmune individuals. DCs generated from both groups demonstrated phenotypes characteristic of DCs and stimulated strong allogeneic MLR. DCs from patients and healthy nonimmune individuals pulsed with the coccidioidal Ag preparation T27K induced lymphocyte proliferation. Mature DCs were much more efficient than immature DCs in these stimulations. Furthermore, restimulation of T27K-primed PBMC with Ag-pulsed DCs generated a C. immitis-specific cellular immune response in PBMC from patients with disseminated coccidioidomycosis as well as healthy nonimmune individuals. These results show that 1) DCs have the capacity to stimulate specific cellular immune responses from patients with disseminated coccidioidomycosis who are nonresponsive to coccidioidal Ag and healthy nonimmune individuals in vitro; 2) DCs can be used to screen coccidioidal Ags as candidates for human vaccine development; and 3) DC therapy may be useful in the treatment of disseminated coccidioidomycosis.

Role of signal sequence in vaccine-induced protection against experimental coccidioidomycosis

The vaccine efficacy of the gene sequence encoding the signal peptide of the antigen known as antigen 2 or proline-rich antigen (Ag2/PRA), an immunodominant antigen present in the cell wall of the fungal pathogen Coccidioides immitis, was investigated in a murine model of coccidioidomycosis. Expression plasmids for Ag2/PRA(1-18) DNA (signal sequence), Ag2/PRA(19-194) DNA (lacking the signal sequence), and Ag2/PRA(1-194) DNA (full length) were inserted in the pVR1012 vector, and the constructs were used to vaccinate the highly susceptible BALB/c mouse strain. Immunization with the signal gene sequence significantly reduced the fungal burden in the lungs and spleens of mice 12 days after intraperitoneal challenge with a lethal dose of 2,500 C. immitis arthroconidia, to a level comparable to the protection induced in mice immunized with the full-length Ag2/PRA(1-194) DNA. The Ag2/PRA(19-194) gene protected mice but to a significantly lower level than the signal sequence or the full-length Ag2 gene. The immunizing capacity of Ag2/PRA(1-18) was not attributable to a nonspecific immunostimulatory effect of DNA, as evidenced by the fact that mice immunized with a frameshift mutation of Ag2/PRA(1-18) were not protected against challenge. Furthermore, a synthetic peptide corresponding to the translated sequence of Ag2/PRA(1-18) DNA protected mice, albeit at a lower level than the Ag2/PRA(1-18) DNA vaccine. The protection induced with the signal gene vaccine correlated with the production of gamma interferon when splenocytes from Ag2/PRA(1-18)-immunized mice were stimulated with recombinant full-length Ag2 and was not associated with the production of anti-Coccidioides immunoglobulin G antibody. This is the first study to establish that a signal peptide sequence alone, administered as a gene vaccine or synthetic peptide, can induce protective immunity against a microbial pathogen.

Coadministration of interleukin 12 expression vector with antigen 2 cDNA enhances induction of protective immunity against Coccidioides immitis

Interleukin 12 (IL-12) plays an important role in the induction of protective immunity against cancer and infectious diseases. In this study we asked whether IL-12 cDNA could increase the protective capacity of the antigen 2 (Ag2) gene vaccine in experimental coccidioidomycosis. Coimmunization of BALB/c mice with a single-chain IL-12 cDNA (p40-L-p35) and Ag2 cDNA, both subcloned into the pVR1012 plasmid, significantly enhanced protection against systemic challenge with 2,500 arthroconidia, as evidenced by a greater-than-1.3-log-unit reduction in the fungal load in the lungs and spleens compared to mice receiving the pVR1012 vector alone, Ag2 cDNA alone, or IL-12 cDNA alone. The enhanced protection was associated with increased gamma interferon secretion; production of immunoglobulin G2a (IgG2a), IgG2b, and IgG3 antibodies to Coccidioides immitis antigen; and the influx of CD4(+) and CD8(+) T cells in lungs and spleens. When challenged by the pulmonary route, mice covaccinated with Ag2 cDNA and IL-12 cDNA were not protected at the lung level but did show a significant reduction in the fungal load in their livers and spleens compared to mice vaccinated with Ag2 cDNA or IL-12 cDNA alone. These results suggest that IL-12 acts as a therapeutic adjuvant to enhance Ag2 cDNA-induced protective immunity against experimental coccidioidomycosis through the induction of Th1-associated immune responses.

Genetic vaccination against Coccidioides immitis: comparison of vaccine efficacy of recombinant antigen 2 and antigen 2 cDNA

Previous studies from our laboratory established that C-ASWS, an alkali-soluble, water-soluble extract from cell walls of Coccidioides immitis, protects mice against lethal challenge with this fungus. The C-ASWS extract contains a glycosylated protein, designated antigen 2 (Ag2), and a polysaccharide antigen. We recently cloned Ag2 cDNA and showed that the recombinant fusion protein elicited strong delayed-type hypersensitivity responses in immunized mice. This investigation was undertaken to determine if the recombinant Ag2 protein, expressed as an Ag2-glutathione S-transferase (GST) fusion protein, or Ag2 cDNA would protect mice against lethal challenge with C. immitis. The recombinant Ag2-GST protein protected BALB/c mice against intraperitoneal challenge with 250 arthroconidia, as assessed by a decrease in fungal CFU in tissues. The Ag2-GST-immunized mice did not show, however, an increased survival during a 30-day period postinfection. By contrast, immunization of mice with Ag2 cDNA ligated into the pVR1012 plasmid engendered protection against intraperitoneal challenge with 2,500 arthroconidia and against pulmonary challenge with 50 arthroconidia. Vaccine efficacy paralleled the development of delayed-type hypersensitivity responses to C. immitis antigen. Whereas mice vaccinated with the recombinant Ag2-GST protein did not mount footpad hypersensitivity to C-ASWS or the recombinant Ag2-GST protein, mice vaccinated with the pVR1012-Ag2 construct mounted a strong footpad hypersensitivity and their spleen cells secreted gamma interferon upon in vitro stimulation with the Ag2-containing C-ASWS extract. This is the first investigation to show that genetic immunization can protect against lethal challenge with C. immitis.

In vitro modulation of proliferation and cytokine production by human peripheral blood mononuclear cells from subjects with various forms of coccidioidomycosis

Using peripheral blood mononuclear cells (PBMC) from individuals with or without coccidioidal delayed-type hypersensitivity (DTH), we examined and attempted to modulate the in vitro responses of PBMC from various donors to the coccidioidal antigen toluene spherule lysate (TSL). Among healthy DTH-positive donors, 100 ng of human recombinant interleukin-10 (IL-10) per ml suppressed both PBMC proliferation (P = 0.01) and gamma interferon (IFN-gamma) and IL-12 production (for both, P < 0.05). In vitro proliferation and production of IFN-gamma and IL-12 by PBMC were significantly higher in DTH-positive donors with active coccidioidomycosis than in healthy, nonimmune controls (P < 0.05) but not in active DTH-negative donors with or without human immunodeficiency virus infection (for both, P > 0.05). Human recombinant IL-12 increased IFN-gamma production by PBMC from active, DTH-positive donors (P = 0.01) but not by PBMC from DTH-negative groups. For healthy DTH-positive donors, the median antigen-reactive cell frequency per 10(5) PBMC was 3.7, compared to 1.7 in DTH-negative donors with active coccidioidomycosis (P = 0.03). These data indicate that the in vitro TSL response is highly dependent on coccidioidal DTH. Not only do PBMC from individuals with DTH appear to respond to TSL, but their response can be modulated in vitro with either IL-10 or IL-12. On the other hand, PBMC from DTH-negative individuals do not respond in vitro to TSL and their response is not modulable, suggesting a lack of antigen response.

Identification of a Coccidioides immitis antigen 2 domain that expresses B-cell-reactive epitopes

Antigen 2 (Ag2), a major immunoreactive component of Coccidioides immitis mycelium- and spherule-phase cell walls, was recently cloned in our laboratory and was shown to elicit T-cell responses in Coccidioides-immune mice. In this investigation, we evaluated recombinant Ag2 (rAg2) and PCR-generated Ag2 truncations for expression of B-cell-reactive epitopes in enzyme-linked immunosorbent and immunoblot assays with sera from patients with active coccidioidomycosis, a hyperimmune goat anti-Ag2 serum, and a murine anti-Ag2 monoclonal antibody that recognizes a conformational epitope. The results established that rAg2 expresses both linear and conformational B-cell-reactive epitopes which are localized to a domain comprised of amino acids 19 through 96 (designated A19-96). Truncations designed to identify epitopes within the A19-96 domain yielded fragments that either were nonreactive (A62-194, A19-61, and A49-79) or showed reduced reactivity (A19-79). Hence, A19-96 was the shortest domain expressing epitopes recognized by the panel of antibodies. The prevalence of antibodies to the A19-96 domain was evaluated in enzyme-linked immunosorbent assays of sera from 28 coccidioidomycosis patients. Antibody reactivity was detected in 79% of the patients' sera, and the level of antibody reactivity was directly correlated with disease severity. Whereas patients with pulmonary disease showed a mean response (A405) of 0.16 +/- 0.04, patients with disseminated coccidioidomycosis showed a mean response of 0.69 +/- 0.17 (P < 0.05). No reactivity was detected with sera from histoplasmosis or blastomycosis patients. The production of a recombinant peptide that expresses C. immitis-specific Ag2 epitopes provides a useful reagent for examining the role of anti-Ag2 antibodies in coccidioidomycosis.

Coccidioides immitis antigen 2: analysis of gene and protein

Antigen 2 is a glycosylated protein present in the cell walls of the dimorphic fungus Coccidioides immitis. Using oligodeoxyribonucleotide (oligo) primers based on the sequences of Ag2 cDNA, the gene encoding Ag2 was cloned from genomic DNA derived from the mycelial phase of C. immitis by PCR. Nucleotide (nt) sequence analyses showed a 582 base pair (bp) ORF disrupted by two introns which are 78 bp and 101 bp long. The deduced primary translation product consists of 194 amino acids (aa), contains an N-terminal putative signal sequence to allow transport into the endoplasmic reticulum, and a C-terminal putative signal sequence to enable a GPI anchor addition. Putative GPI anchor/cleavage site and O-glycosylation sites, as well as phosphorylation and myristoylation sites are also present. On the basis of these analyses, we predict that a prepro-Ag2 undergoes a post-translational modification to yield the mature glycosylated Ag2 protein which is anchored on the extracellular plasma membrane of mycelial and spherule-phase cells.

Molecular cloning and characterization of Coccidioides immitis antigen 2 cDNA

Previous experiments have provided evidence that Coccidioides immitis antigen 2 (Ag2) is a major T-cell-reactive component of mycelia and spherule cell walls. Here we report the identification and cloning of the cDNA that encodes Ag2 from a lambda ZAP cDNA expression library constructed from spherule-derived RNA. DNA sequence analysis established that the 1,255-bp clone contains a 174-bp 5' untranslated region, a 582-bp open reading frame which encodes for a protein consisting of 194 amino acids, and a 375-bp 3' untranslated region, including a poly(A) tail. The recombinant Ag2 protein has a predicted molecular mass of 19.5 kDa and contains an 18-amino-acid N terminus which has been tentatively identified as a signal peptide. The Ag2 cDNA was ligated into the pGEX-4T-3 vector and expressed in Escherichia coli TG-1 cells as a glutathione S-transferase fusion protein. The recombinant fusion protein showed reactivity with sera from patients with coccidioidomycosis and elicited delayed-type footpad hypersensitivity responses in Coccidioides-immune mice. These results suggest that the Ag2 cDNA can be used for the large-scale production of this immunologically important protein.

Production of a murine monoclonal antibody that recognizes an epitope specific to Coccidioides immitis antigen 2

Antigen 2 (Ag2) has been implicated as a T-cell-reactive component of the pathogenic fungus Coccidioides immitis. We report the production of a murine monoclonal antibody (MAb) of the immunoglobulin G2a isotype that recognizes an epitope specific to C. immitis Ag2. This specificity was evidenced by the finding that the MAb did not recognize other antigens present in coccidioidin or spherulin and did not show reactivity with antigenic extracts from Histoplasma capsulatum or Blastomyces dermatitidis. The epitope was labile to enzymatic digestion with pronase but resistant to treatment with glycolytic enzymes and to periodate oxidation. This peptide epitope appears to require conformational structure on the basis that it was not recognized by the MAb in immunoblots of antigen that had been electrophoresed in polyacrylamide gels under denaturing, reducing conditions. Immunoaffinity chromatography of spherulin on columns containing the MAb established that the MAb was effective as a ligand for isolating Ag2 from heterogeneous extracts. The production of a MAb which recognizes an Ag2-specific epitope and its utility as a ligand for isolating Ag2 will provide a valuable reagent for studies of this immunologically important antigen.

Killing of Coccidioides immitis by human peripheral blood mononuclear cells

The ability of human peripheral blood mononuclear cells (MNL) obtained from healthy donors to kill the fungus Coccidioides immitis was examined in vitro with an assay that uses a single fungal particle per well. MNL killed 25.0% +/- 3.5% of a coccidioidal arthroconidial target, compared with the 4.7% +/- 2.9% killed by polymorphonuclear leukocytes obtained from the same donors (P = 0.012). Arthroconidial killing by MNL was not dependent on donor delayed dermal hypersensitivity to spherulin. Killing of another fungal target, Candida glabrata, was not significantly different between MNL and polymorphonuclear leukocytes (P = 0.783). Depletion of monocytes from MNL with Sephadex G-10 resulted in a significant reduction in arthroconidial killing (21.4% +/- 13.6% versus 2.4% +/- 3.4%; P = 0.025), while enrichment of monocytes by Percoll density gradient centrifugation or plastic adherence resulted in significantly increased arthroconidial killing compared with that by MNL (P = 0.005 and 0.001, respectively). Killing of 96-h spherules by MNL was 7.3% +/- 3.1%, significantly less than the 21.4% +/- 2.8% killing of arthroconidia in the same experiments (P = 0.016). Incubation of MNL with human recombinant gamma interferon or tumor necrosis factor alpha did not result in increased MNL killing of coccidioidal arthroconidia under various conditions. These results suggest that MNL have an inherent ability to kill coccidioidal arthroconidia in vitro which is not dependent on prior host exposure to C. immitis. This activity appears to reside in peripheral blood monocytes.

Coccidioides immitis fractions which are antigenic for immune T lymphocytes

The principal mechanism of resistance to coccidioidomycosis in experimental animals has been reported to be T-cell-mediated immunity. We have generated a Coccidioides immitis antigen-specific murine T-cell line to identify specific macromolecules capable of eliciting an immune mouse T-cell proliferative response. The murine T cells were stimulated in vitro with a soluble conidial wall fraction (SCWF), which has been previously characterized by humoral and cellular immunoassays. The SCWF was separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrotransferred to a nitrocellulose membrane, and the stained blot was cut into seven pieces based on the molecular size of the SCWF components. The nitrocellulose membrane strips were converted into antigen-bearing particles and tested in a T-cell proliferation assay. Antigenic components of the SCWF in the molecular size range of 43 to 66 kDa were identified as the most immunoreactive. In a parallel study, we used a cDNA expression library derived from mRNA of the mycelial phase of C. immitis, which was constructed in lambda gt11 to identify clones that encoded T-cell-reactive fusion proteins (FPs). The cDNA library was screened by using anti-SCWF rabbit serum, and the FPs expressed in Escherichia coli were isolated and tested for T-cell response in the same manner as the SCWF components. The nucleotide sequence of a 0.2-kb cDNA insert encoding a protein which elicited vigorous T-cell response was determined. The isolated cDNA insert hybridized to a single 1.9-kb mRNA band in a Northern blot of the total RNA fraction of the mycelial phase of C. immitis. Antibody with affinity for the T-cell-reactive FP was isolated from anti-SCWF rabbit serum by solid-phase immunoadsorption. The FP-specific antibody reacted with a 47-kDa polypeptide in Western blots (immunoblots) of the SCWF. The same antibody preparation was used for immunoelectron microscopy to show that the FP was localized in the walls of arthroconidia and spherules of C. immitis. Attempts to clone and sequence the entire gene which encodes the T-cell-reactive protein are under way. The results of this study should lead to the determination of the complete structure of an important T-cell-stimulating antigen of C. immitis.

The maternal immune response in coccidioidomycosis. Is pregnancy a risk factor for serious infection?

Seven subjects with prior coccidioidal disease and three with active Coccidioides immitis infection during their first trimester were studied during pregnancy and postpartum to determine their general and antigen-specific cell-mediated immune status. All ten were white and carried their pregnancies to term without incident. Decreases in total lymphocytes and T-helper and T-suppressor subsets were noted during the third trimester, presumably secondary to an increase in plasma volume. Lymphocyte responses to the mitogens phytohemagglutinin, concanavalin A, and pokeweed were mildly decreased late in pregnancy, with significant intrasubject and intersubject variation. Responses to tetanus antigen were consistently and significantly lower as pregnancy progressed, rising above first trimester levels by 12 weeks postpartum. A similar pattern of response was noted with spherulin antigen for the seven subjects with previously demonstrated coccidioidal immunity. The three subjects with active coccidioidomycosis either failed to mount a significant spherulin immune response or demonstrated an early response that fell as pregnancy progressed. This antigen-specific immune suppression continued for up to 16 months postpartum despite the fact that there was no clinical evidence of coccidioidal activity beyond the first trimester. Thus, while all three completed pregnancy without complication, the data suggest that significantly increased maternal risk may be present when active coccidioidomycosis and pregnancy occur together. This risk may be greatest among darker-skinned individuals who become infected during the latter half of pregnancy.

An immunoreactive apoglycoprotein purified from Coccidioides immitis

Deglycosylation of glycoproteins in a lysate of spherules of Coccidioides immitis has permitted purification and partial characterization of a proline-rich pronase-sensitive antigen. Moreover, soluble antigen specifically stimulated lymphocytes from persons with dermal delayed-type hypersensitivity to coccidioidal antigens. When related to reference coccidioidin by tandem two-dimensional immunoelectrophoresis, the antigen fused in the anodal region with a specific reference antigen (antigen 2). It did not show identity with coccidioidal antigens used in conventional serologic assays. Although immunoblots of the purified protein with monospecific rabbit antiserum showed a single antigen at 33 kDa, the parent spherule lysate bound the same antibody in a broad band between 70 and greater than 200 kDa, which could be explained by microheterogeneity of glycosylation. Immunoelectron microscopy using affinity-purified human antibodies localized the antigen to the cell wall and internal septa of spherules. These findings suggest that the apoglycoprotein may be important in human immune responses to coccidioidal infection.

Interaction of human peripheral blood mononuclear cells with Coccidioides immitis arthroconidia

We explored the in vitro interaction of human peripheral blood mononuclear cells with the arthroconidial stage of the fungus Coccidioides immitis. Fresh peripheral blood monocytes in an adherent monolayer were capable of ingesting C. immitis. Further, peripheral blood monocytes from either skin-test-positive or skin-test-negative donors significantly decreased the in vitro growth of C. immitis when coccidioidal arthroconidia were incubated with monocytes. Peripheral blood mononuclear cells also reduced fungal incorporation of the chitin precursor N-acetyl glucosamine. Cell fractions consisting predominantly of monocytes were significantly more active in this regard than fractions containing predominantly lymphocytes. Moreover, this activity was independent of the coccidioidal skin-test status of the donor. We conclude that human fresh peripheral blood mononuclear cells are able to phagocytize C. immitis arthroconidia and have the ability to inhibit its growth in vitro. That these abilities are independent of the immune status of the donor supports the possibility that the peripheral blood monocyte may contribute to the early defense against initial coccidioidal infection.

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.

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.

Experimental coccidioidomycosis: effects of cyclophosphamide in immunologic responses

Rats were infected with Coccidioides immitis and injected with cyclophosphamide three days pre or post infection. Administration of the drug before the infection caused enhancement of DTH response and decrease of the colony forming units (CFU). Conversely, injection of the drug three days post infection produced contrary effects, indicating that a normal T-cell function is essential as a defense mechanism in C. immitis infection.

The prevalence of cellular immunity to coccidioidomycosis in a highly endemic area

Intradermal skin test reactivity to spherulin and coccidioidin and in vitro spherulin-induced lymphocyte transformation were used to assess cellular immunity in healthy subjects and patients with acute, self-limited coccidioidomycosis (cocci). The objectives of this study were to evaluate the relative sensitivities of the two assays in assessing cellular immunity to cocci, especially in long-term residents of an endemic area (Tucson) and, based on data from both assays, determine the prevalence of detectable cellular immunity to cocci in this highly endemic area. The lymphocyte transformation assay appeared to be more sensitive than the skin test in assessing long-term immune status, and the prevalence of detectable immunity to cocci in this highly endemic area was only 75% in long-term residents. This is much lower than previous prevalence estimates (90%) in other endemic areas. The absence of a demonstrable cell-mediated immunity may indicate either no prior antigen exposure (infection) or previous remote exposure with a diminished immune response (no reexposure to boost immunity). A possible explanation for the lower prevalence of immunity to cocci in this endemic area may relate to the increased urbanization of the Southwest in the past several years. Therefore, the clinical suspicion of acute cocci should not be restricted to recent arrivals to endemic areas.

Antigenic heterogeneity of an alkali-soluble, water-soluble cell wall extract of Coccidioides immitis

The antigenic composition of an alkali-soluble, water-soluble cell wall extract of Coccidioides immitis, designated C-ASWS, was assessed by two-dimensional immunoelectrophoresis against goat antisera to C-ASWS and coccidioidin. The results established that C-ASWS from mycelia or spherule cell walls is heterogeneous in composition, containing two distinct antigenic components. One is present as a polymer that is antigenically identical to a polymeric antigen in coccidioidin, designated antigen 2. The other component detected in C-ASWS presented an unusual precipitin pattern in that a cathodal leg was demonstrable in the absence of an anodal leg. This incomplete precipitinogen was also detected in coccidioidin. In addition to the finding that C-ASWS is antigenically heterogeneous, the results provide evidence that the conformational and/or configurational structure of the C-ASWS antigen 2 (or antigen 2-like polymer) is altered during physicochemical extraction. This conclusion is based upon the finding that the immunoelectrophoretic profile of the C-ASWS polymer differs from that of coccidioidin antigen 2. The C-ASWS polymer is characterized by having a small cathodal precipitin peak connected to a large anodal peak, whereas coccidioidin antigen 2 is characterized by a predominant cathodal peak.

Coccidioidomycosis in acquired immune deficiency syndrome. Depressed humoral as well as cellular immunity

Progressive pulmonary coccidioidomycosis has not been previously reported in the setting of acquired immune deficiency syndrome (AIDS). A patient with AIDS, progressive pulmonary coccidioidomycosis, Pneumocystis carinii pneumonia, and disseminated cytomegalovirus is described. Diagnosis of these opportunistic pathogens was made by bronchoalveolar lavage and transbronchial lung biopsy. Results of traditional complement fixation serologic testing for cytomegalovirus were negative; however, the more sensitive enzyme-linked immunosorbent assay did indicate infection. Coccidioidal complement fixation tests, precipitin tests, counter-immunoelectrophoresis, and immunodiffusion tests demonstrated negative findings. These results provide additional evidence that some patients with AIDS have defects in humoral as well as cellular immunity.

Reactivity of alkali-soluble, water-soluble cell wall antigen of Coccidioides immitis with anti-Coccidioides immunoglobulin M precipitin antibody

The alkali-soluble, water-soluble cell wall antigen of Coccidioides immitis (C-ASWS) mycelia and spherules was shown to react with anti-Coccidioides immunoglobulin M (IgM) precipitin antibody, both in the classical tube precipitin test and in the immunodiffusion assay for tube precipitin antibody (IDTP). The reactions obtained between C-ASWS and reference IgM precipitin antibody were identical to the reaction obtained when reference coccidioidin (CDN) was used. Definitive proof that C-ASWS extracts contain antigenic determinants that are reactive with IgM tube precipitin antibody was obtained by solid-phase immunoadsorption. Elution of reference IDTP antiserum over a column containing mycelium C-ASWS coupled to Sepharose 4B completely adsorbed precipitin antibody; i.e., reactivity in the IDTP was demonstrable in the column eluate but not in the column effluent fraction. The antigenic composition of C-ASWS extracts was evaluated and compared with that of CDN by two-dimensional immunoelectrophoresis against burro anti-CDN. The results established that both mycelium and spherule C-ASWS contain antigenic determinants in common with only one antigen present in CDN. The latter, designated antigen 2, is a large polymer which is predominant among the antigenic components in CDN. On a dry weight comparison, antigen 2 determinants were most concentrated in spherule C-ASWS, followed by mycelium C-ASWS and reference IDTP antigen. The finding that C-ASWS extracts are reactive with IgM tube precipitin antibody and are antigenically identical to antigen 2 in CDN suggests that antigen 2 is the biologically active component of CDN in tube precipitin assays.

Coccidioides immitis vaccine: potential of an alkali-soluble, water-soluble cell wall antigen

C-ASWS-M, the alkali-soluble, water-soluble cell wall antigen of Coccidioides immitis mycelia, was evaluated for its vaccine potential in mice. Vaccination with 0.5-, 1.5-, or 3-mg doses of C-ASWS-M in complete Freund adjuvant provided a significant level of protection against intraperitoneal challenge with 1,500 arthroconidia (P < 0.0001 with each dose). Vaccination with 1 mg of C-ASWS-M protected mice against intranasal challenge with 50 (P < 0.05) and 500 (P < 0.01) arthroconidia, but not against intranasal challenge with 1,500 arthroconidia (P > 0.05).

Specificity of immunoglobulin E in coccidioidomycosis and correlation with disease involvement

Serum immunoglobulin E (IgE) antibodies were quantitated in 26 patients with active pulmonary coccidioidomycosis, 59 patients with active disseminated disease, 12 patients in clinical remission, and 91 healthy subjects. Significant differences were obtained in IgE serum levels of patients with active disease versus healthy subjects (P less than 0.0001). Patients with pulmonary coccidioidomycosis did not differ in their IgE levels when compared with patients with disseminated disease. However, serum IgE levels were significantly increased in patients with disease involving two or more organ systems when compared with patients with pulmonary disease or extrapulmonary disease involving a single organ system (P less than 0.02). Total serum IgE correlated with anti-Coccidioides IgE (P less than 0.001), but with only six exceptions, patients with anti-Coccidioides IgE also exhibited IgE antibodies to 1 or more of 12 common allergens. The correlation between hyperproduction of IgE and disease severity coupled with the depressed cell-mediated immune status of patients with this disease suggests a defect(s) in the T-lymphocyte population which functions to regulate IgE synthesis.

Stimulation and suppression of cell-mediated immunity by endosporulation antigens of Coccidioides immitis

The culture filtrate of Coccidioides immitis induced to replicate in its parasitic phase in vitro, termed endosporulation antigens (EA), was assayed for ability to stimulate human lymphocyte blastogenesis in vitro. Stimulation of lymphocytes from skin test-positive healthy subjects by EA was comparable to stimulation by spherulin at optimal dilutions, but EA are 500 times more potent when compared on the basis of weight. Both preparations slightly stimulated lymphocytes from skin test-negative subjects. Heating or dialysis of EA enhanced the effect on skin test-positive subjects, but concentration depressed it. Concentrated EA also depressed nonspecific stimulation caused by phytohemagglutinin. Dialysis of concentrated EA reduced the ability to depress responses. EA from an avirulent strain of C. immitis were as stimulatory as EA from a virulent strain, but concentrating the former did not produce as much depression as concentrating the latter did. A survey of subjects with an optimal dose of EA in lymphocyte transformation showed that EA could separate skin test-positive from -negative subjects as well as spherulin could. The survey also showed that a delta cpm (the difference of incorporated counts of tritiated thymidine per minute in the presence or absence of the reagent) of 10,000 is useful for this separation. These results also indicate the presence of suppressive substances in EA which are only partially dialyzable and which were significantly more prominent in a preparation from the virulent strain.

Comparisons of mycelia- and spherule-derived antigens in cellular immune assays of Coccidioides immitis-infected guinea pigs

The biological activities of four Coccidioides antigens were compared in skin test, macrophage migration inhibitory factor (MIF), and lymphocyte transformation (LT) assays fo 137 Coccidioides-infected and 20 noninfected guinea pigs. Antigens included: C-ASWS-M, the alkali-soluble, water-soluble cell wall extract from mycelia of C. immitis; C-ASWS-S, the alkali-soluble, water-soluble cell wall extract from spherules; CDN-TS, a toluene-induced lysate of C. immitis mycelia; and spherulin, an autolysate obtained from spherules. CDN-TS proved significantly more reactive (P less than 0.0001) in skin tests, eliciting a mean induration of 11.6 mm as compared with indurations of 6.6, 6.4, and 6.1 mm obtained with C-ASWS-S spherulin, and C-ASWS-M, respectively. CDN-TS, C-ASWS-S, and spherulin were equally reactive in MIF assays and elicited migration inhibitions of 31.8, 30.8, and 30.7%. C-ASWS-M was significantly less reactive (P less than 0.001), with a mean response of 23.5%. The highest level of activity in LT assays was obtained with C-ASWS-S with a mean response of 5,636 delta cpm as compared with responses of 3,624, 3,439, and 3,580 delta cpm with CDN-TS, spherulin, and C-ASWS-M, respectively (P less than 0.01). All antigens were effective in distinguishing responses of infected versus noninfected guinea pigs.

Cross-reactivity between antigens of Coccidioides immitis, Histoplasma capsulatum and Blastomyces dermatitidis in lymphocyte transformation assays

The cross-reactivity of four Coccidioides antigens, three Histoplasma antigens, and two Blastomyces antigens were determined in lymphocyte transformation assays of 11 coccidioidin-reactive, histoplasmin-nonreactive subjects (group I), 13 coccidioidin-nonreactive, histoplasmin-reactive persons (group II), and 13 subjects who were skin test negative to both antigens (group III). Mycelial and yeast (or spherule)-phase antigens of the three fungi were included. Significant cross-reactivity was obtained with both coccidioidins, spherulin, and the alkali-soluble, water-soluble cell wall antigen of C. immitis, to the extent that the responses of histoplasmin-reactive persons were not statistically different (P > 0.05) from those of coccidioidin-reactive persons. In contrast, optimal dilutions of Histoplasma mycelial and yeast-phase lysates effectively distinguished (P < 0.01) responses of histoplasmin- and coccidioidin-reactive persons. The alkali-soluble cell wall antigen of H. capsulatum showed extensive cross-reactivity at most concentrations and was markedly stimulatory to lymphocytes of skin test-negative persons. Blastomycin elicited significant cross-reactions in histoplasmin-sensitive subjects and to a lesser extent in coccidioidin-sensitive subjects. The alkali-soluble cell wall antigen cross-reacted in cultures of histoplasmin-reactive persons but not in those of coccidioidin-reactive persons. All antigens effectively distinguished (P < 0.001) homologous responses of skin test-positive persons (groups I and II) from those of skin test-negative persons (group III). The extensive cross-reactivity in lymphocyte transformation assays in the absence of cross-reactivity in skin tests suggests that these two immune responses may be mediated by different T lymphocyte populations, may be elicited by different antigenic components, or both.

Brucella antigen preparations for in vitro lymphocyte immunostimulation assays in bovine brucellosis

Three Brucella antigen preparations, Brucella abortus soluble antigen, B. abortus strain 45/20 enriched protein antigen, and B. melitensis enriched protein antigen, were compared in terms of their ability to induce specific in vitro lymphocyte immunostimulation responses. Lymphocytes were prepared from peripheral blood of cattle with different exposure experiences to B. abortus organisms. Lymphocytes were processed by the Ficoll-diatrizoate technique, and results were assayed for [3H]tymidine incorporation into DNA by liquid scintillation spectrometry. The three Brucella antigen preparations were compared both at the optimal concentrations of protein and on an equal-dry-weight basis. The results were evaluated in terms of specific lymphocyte immunostimulation responses induced by each preparation and the degree of correlation with infection. B. abortus soluble antigen-induced lymphocyte immunostimulation response correlated best with infection status followed by B. abortus 45/20 and B. melitensis enriched protein antigens. The implications of these findings are discussed and a hypothesis is proposed.

Antigenic analysis of coccidioidin and spherulin determined by two-dimensional immunoelectrophoresis

Immunological tests are valuable aids for diagnosis of mycotic infections and, in some cases, as objective guides for clinical management and prognosis. The usefulness of these procedures is limited to the extents that crude antigen preparations are employed, that these are difficult to standardize uniformly, and that they contain antigens common to several species of pathogenic fungi. Analysis by two-dimensional immunoelectrophoresis methods of the two crude preparations used for coccidioidomycosis demonstrated that coccidioidin contained at least 26 antigens, with 10 of these found also in spherulin. In addition, spherulin contained two antigens not demonstrated in coccidioidin. No single test detected all antigens present, and multiple procedures were required to display the complete array of antigens. A reference system was established for coccidioidin and precipitated immunoglobulins from a burro hyperimmunized with coccidioidin. Evaluation of the reference system demonstrated that it was highly reproducible with respect to the reagents used, to repeated tests by the same person, and to comparative tests by two individuals using the same reagents. Applications of this reference system for standardization of reagents, for detecting common antigens, for monitoring successive steps during fractionation of crude preparations, and for fingerprinting strains for ecological and epidemiological studies are presented.