Validation of western blot for Histoplasma capsulatum antibody detection assay

Multi-epitope protein production and its application in the diagnosis of opisthorchiasis

BACKGROUND

Opisthorchiasis and cholangiocarcinoma (CCA) continue to be public health concerns in many Southeast Asian countries. Although the prevalence of opisthorchiasis is declining, reported cases tend to have a light-intensity infection. Therefore, early detection by using sensitive methods is necessary. Several sensitive methods have been developed to detect opisthorchiasis. The immunological detection of antigenic proteins has been proposed as a sensitive method for examining opisthorchiasis.

METHODS

The Opisthorchis viverrini antigenic proteins, including cathepsin B (OvCB), asparaginyl endopeptidase (OvAEP), and cathepsin F (OvCF), were used to construct multi-antigenic proteins. The protein sequences of OvCB, OvAEP, and OvCF, with a high probability of B cell epitopes, were selected using BepiPred 1.0 and the IEDB Analysis Resource. These protein fragments were combined to form OvCB_OvAEP_OvCF recombinant DNA, which was then used to produce a recombinant protein in Escherichia coli strain BL21(DE3). The potency of the recombinant protein as a diagnostic target for opisthorchiasis was assessed using immunoblotting and compared with that of the gold standard method, the modified formalin-ether concentration technique.

RESULTS

The recombinant OvCB_OvAEP_OvCF protein showed strong reactivity with total immunoglobulin G (IgG) antibodies against light-intensity O. viverrini infections in the endemic areas. Consequently, a high sensitivity (100%) for diagnosing opisthorchiasis was reported. However, cross-reactivity with sera from other helminth and protozoan infections (including taeniasis, strongyloidiasis, giardiasis, E. coli infection, enterobiasis, and mixed infection of Echinostome spp. and Taenia spp.) and no reactivity with sera from patients with non-parasitic infections led to a reduced specificity of 78.4%. In addition, the false negative rate (FNR), false positive rate (FPR), positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy were 0%, 21.6%, 81.4%, 100%, and 88.9%, respectively.

CONCLUSIONS

The high sensitivity of the recombinant OvCB_OvAEP_OvCF protein in detecting opisthorchiasis demonstrates its potential as an opisthorchiasis screening target. Nonetheless, research on reducing cross-reactivity should be undertaken by detecting other antibodies in other sample types, such as saliva, urine, and feces.

Histoplasma antigens as novel players for the development of new enzyme immunoassays for the serodiagnosis of histoplasmosis: A comparative study of their analytical performance

Definitive diagnosis of histoplasmosis relies on culture and/or cytology/histopathology; however, these procedures have limited sensitivity and cultures are time-consuming. Antibodies detection by immunodiffusion has low sensitivity in immunocompromised individuals and uses histoplasmin (HMN), a crude antigenic extract, as reagent. Novel protein antigen candidates have been recently identified and produced by DNA-recombinant techniques to obtain standardized and specific reagents for diagnosing histoplasmosis. To compare the analytical performance of novel enzyme-linked immunosorbent assays (ELISAs) for antibodies testing for diagnosing histoplasmosis using different Histoplasma capsulatum antigens as reagents. The H. capsulatum 100 kDa protein (Hcp100), the M antigen and its immunoreactive fragment F1 were produced by DNA-recombinant techniques. Galactomannan was purified from both the yeast and mycelial cell walls (yGM and mGM, respectively). The analytical performance of the ELISA tests for the serological detection of antibodies against these antigens was evaluated and compared with those obtained using HMN as reagent. Antibodies detection by the Hcp100 ELISA demonstrated 90.0% sensitivity and 92.0% specificity, versus 43.3% sensitivity and 95.0% specificity of the M ELISA, 33.3% sensitivity and 84.0% specificity of the F1 ELISA, 96.7% sensitivity and 94.0% specificity of the yGM ELISA, 83.3% sensitivity and 88.0% specificity of the mGM ELISA, and 70.0% sensitivity and 86.0% specificity for the HMN ELISA. In summary, Hcp100 is proposed as the most promising candidate for the serodiagnosis of histoplasmosis. The primary immunoreactive element in HMN proved to be GM rather than the M antigen. Nevertheless, a higher incidence of cross-reactions was noted with GM compared to M.

Histoplasmosis at a Reference Center for Infectious Diseases in Southeast Brazil: Comparison between HIV-Positive and HIV-Negative Individuals

Objectives: Histoplasmosis is a systemic mycosis, present globally. We aimed to describe cases of histoplasmosis (Hc) and to establish a risk profile associated with Hc in HIV-infected patients (HIV+). Methods: This was a retrospective study of patients with a clinical laboratory diagnosis of Hc. Data were fed into REDCap, and statistical analysis was performed with R. Results: We included 99 records, 65 HIV+ and 34 HIV-. Average age was 39 years. Median time from onset to diagnosis was 8 weeks in HIV- and 22 weeks in HIV+. Disseminated histoplasmosis occurred in 79.4% of HIV+, vs. 36.4% of HIV- patients. Median CD4 count was 70. Co-infection with tuberculosis was present in 20% of HIV+ patients. Blood cultures were positive in 32.3% of HIV+ vs. 11.8% of HIV- (p = 0.025) patients; bone marrow culture was positive in 36.9% vs. 8.8% (p = 0.003). Most HIV+ patients (71.4%) were hospitalized. On univariate analysis, anemia, leukopenia, intensive care, use of vasopressors and mechanical ventilation were associated with death in HIV+ patients. Conclusions: Most of our patients with histoplasmosis were HIV+, presenting advanced AIDS. Diagnosis was late in HIV+ patients, and they frequently presented disseminated Hc, required hospitalization, and died. Early screening for Hc in HIV+ and drug-induced immunosuppressed patients is crucial.

Immunologic Diagnosis of Endemic Mycoses

The endemic mycoses blastomycosis, coccidioidomycosis, histoplasmosis, paracoccidioidomycosis, cryptococcosis, sporotrichosis, talaromycosis, adiaspiromycosis, and emergomycosis are mostly caused by geographically limited thermally dimorphic fungi (except for cryptococcosis), and their diagnoses can be challenging. Usual laboratory methods involved in endemic mycoses diagnosis include microscopic examination and culture of biological samples; however, serologic, histopathologic, and molecular techniques have been implemented in the last few years for the diagnosis of these mycoses since the recovery and identification of their etiologic agents is time-consuming and lacks in sensitivity. In this review, we focus on the immunologic diagnostic methods related to antibody and antigen detection since their evidence is presumptive diagnosis, and in some mycoses, such as cryptococcosis, it is definitive diagnosis.

Pulmonary Histoplasmosis

Histoplasmosis is one of the most frequent causes of fungal respiratory infection in endemic regions, has a broad spectrum of clinical manifestations and can present in several forms. The extent of disease is determined by the number of conidia inhaled, the immune response of the host and the integrity of the respiratory tract. From an initial and most benign form, acute pulmonary histoplasmosis (an influenza-like illness that is typically asymptomatic or mild in persons without prior immune compromise), histoplasmosis can become a lifethreatening progressive disseminated infection (PDH) that affects mainly immunocompromised patients, with high morbidity and mortality. Chronic pulmonary histoplasmosis is an uncommon manifestation of Histoplasma infection, with features similar to pulmonary tuberculosis, and if it remains undiagnosed or untreated it also can cause significant morbidity. Some rare but serious complications may also occur that are produced by an excessive immune response, such as mediastinal fibrosis, histoplasmoma and broncholithiasis. Histoplasmosis is highly endemic in regions of North, Central and South America as well as being reported in parts of Asia and Africa. The risk of histoplasmosis is greatest in patients with HIV infection, especially those with CD4⁺ counts of <200 cells/μL. We review clinical manifestations, radiological findings and treatment options according to the clinical form (induction therapy and maintenance therapy), as well as different diagnosis tools and new laboratory tests that have been recently developed and validated and are becoming widely available. These should have an impact in reducing time for diagnosis and starting therapy and in reducing morbidity and mortality, especially in patients with HIV infection, where histoplasmosis is currently estimated to be responsible for 5-15% of AIDS-related deaths.

Acute Pulmonary Histoplasmosis Following COVID-19: Novel Laboratorial Methods Aiding Diagnosis

The acute form of histoplasmosis usually occurs after the exposition of more than one individual to a common environmental source harboring Histoplasma capsulatum. Here, we present two cases of acute pulmonary histoplasmosis seen within two weeks at a reference center for infectious diseases at Rio de Janeiro, Brazil. The patients did not present a common epidemiologic history for histoplasmosis, however both presented COVID-19 before the onset of histoplasmosis symptoms. Due to the difficulties in the diagnosis of acute histoplasmosis, novel laboratory methods such as Western Blot and PCR were included in the investigation of these cases. Both patients presented negative cultures for H. capsulatum and negative urinary galactomannan. However, they presented H and M bands in the Western blot as well as a positive H. capsulatum DNA detection in sputum. These results were available approximately 36 h after sample collection, fastening the beginning of treatment of one patient. Both patients progressed well with itraconazole treatment. These cases suggest that COVID-19 may facilitate the development of acute pulmonary histoplasmosis and, therefore, clinicians must be aware of this differential diagnosis in patients from endemic areas with fever and coughing after recovery from COVID-19.

Diagnosis of histoplasmosis: current status and perspectives

Histoplasmosis is a worldwide-distributed systemic mycosis caused by the dimorphic fungus Histoplasma capsulatum. Its clinical manifestations range from subclinical or mild respiratory illness to progressive disseminated histoplasmosis (PDH), a life-threatening disease, whose accurate diagnosis is still challenging and limited in many countries, where this disease is highly endemic. In this regard, Histoplasma antigen testing is now included in the WHO Essential Diagnostics List. The final diagnosis of histoplasmosis is established by culture and/or visualization of the yeast cells by cytology or histopathology using specific stains. However, both procedures have limited sensitivity to detect the disease and cultures are time-consuming. Antibody detection assays are effective for the subacute and chronic clinical forms of histoplasmosis. However, their sensitivity is low in the immunocompromised host. Several molecular "in-house" tests were also developed and showed promising results, but none of these tests are commercially available and their standardization and validation are still pending. Antigen detection assays have high sensitivity in PDH cases and are of great value for the follow-up of patients with histoplasmosis; however, cross-reactivity with other related fungi are common. In addition, this assay is expensive and only performed in few laboratories. Novel protein antigen candidates have been recently identified and produced by DNA-recombinant techniques in order to obtain standardized and specific reagents for the diagnosis of histoplasmosis, as opposed to the unspecific antigens or crude extracts currently used. This review describes the currently available assays, highlighting their strengths and limitations and reports the latest approaches to achieve reliable and rapid diagnostic tests for histoplasmosis. KEY POINTS: • PDH causes thousands of deaths per year globally. • Rapid accurate diagnosis of PDH is unfeasible in many regions. • Fast, accurate, and low-cost diagnostic alternatives are currently under development.

Immunoproteomics Reveals Pathogen's Antigens Involved in Homo sapiens-Histoplasma capsulatum Interaction and Specific Linear B-Cell Epitopes in Histoplasmosis

Histoplasmosis is one of the most frequent systemic mycosis in HIV patients. In these patients, histoplasmosis has high rates of morbidity/mortality if diagnosis and treatment are delayed. Despite its relevance, there is a paucity of information concerning the interaction between Histoplasma capsulatum and the human host, especially regarding the B-cell response, which has a direct impact on the diagnosis. Culture-based “gold-standard” methods have limitations, making immunodiagnostic tests an attractive option for clinical decisions. Despite the continuous development of those tests, improving serological parameters is necessary to make these methods efficient tools for definitive diagnosis of histoplasmosis. This includes the determination of more specific and immunogenic antigens to improve specificity and sensitivity of assays. In this study, we performed a co-immunoprecipitation assay between a protein extract from the yeast form of H. capsulatum and pooled sera from patients with proven histoplasmosis, followed by shotgun mass spectrometry identification of antigenic targets. Sera from patients with other pulmonary infections or from healthy individuals living in endemic areas of histoplasmosis were also assayed to determine potentially cross-reactive proteins. The primary structures of H. capsulatum immunoprecipitated proteins were evaluated using the DNAStar Protean 7.0 software. In parallel, the online epitope prediction server, BCPREDS, was used to complement the B-epitope prediction analysis. Our approach detected 132 reactive proteins to antibodies present in histoplasmosis patients’ sera. Among these antigens, 127 were recognized also by antibodies in heterologous patients’ and/or normal healthy donors’ sera. Therefore, the only three antigens specifically recognized by antibodies of histoplasmosis patients were mapped as potential antigenic targets: the M antigen, previously demonstrated in the diagnosis of histoplasmosis, and the catalase P and YPS-3 proteins, characterized as virulence factors of H. capsulatum, with antigenic properties still unclear. The other two proteins were fragments of the YPS-3 and M antigen. Overlapping results obtained from the two aforementioned bioinformatic tools, 16 regions from these three proteins are proposed as putative B-cell epitopes exclusive to H. capsulatum. These data reveal a new role for these proteins on H. capsulatum interactions with the immune system and indicate their possible use in new methods for the diagnosis of histoplasmosis.

Improved serodiagnosis of histoplasmosis by use of deglycosylated extracellular released antigens of Histoplasma capsulatum

The diagnosis of histoplasmosis depends on various approaches: direct clinical examination, fungus isolation from cultures of clinical samples, histopathological evaluation, and serological testing. In serodiagnostic assays, the Histoplasma capsulatum H and M antigenic glycoproteins have been extensively used. However, both antigens showed limitations attributed mainly to their cross-reactivity with glycoproteins from other pathogenic fungi, which compromises specificity, and generates false positives, misdiagnosis, and therapeutic failure. In this work, we deglycosylated extracellular released antigens from the Venezuelan 7090 H. capsulatum clinical isolate, using chemical and enzymatic methods and evaluated their effectiveness by indirect enzyme-linked immunosorbent assay (ELISA) with sera from patients with either histoplasmosis or PCM. Prior to deglycosylation, the extracellular released antigen showed 62% of sensitivity 66% of specificity and 68% of cross-reactivity with paracoccidioidomicosis sera. The chemically deglycosylated extracellular released antigen, for 8 or 18  h showed 72 and 52% sensitivity with 98% and 92% specificity, respectively. Moreover, cross-reactivity with Paracoccidioides decreased to 4 and 16%, following deglycosylation for 8 or 18 h, respectively. The enzymatically treated antigen showed 52% of sensitivity, 92% of specificity and 8% cross-reactivity against Paracoccidioides. Deglycosylation of the H. capsulatum antigen improves its specificity and decreases its cross-reactivity against Paracoccidioides when using indirect ELISA for serodiagnosis. Therefore, it is recommended to deglycosylate the fungal extracellular released antigen for clinical serodiagnosis, and to monitor humoral immune responses during therapy of patients with the different clinical forms of histoplasmosis.

Histoplasma capsulatum 100-kilodalton antigen: recombinant production, characterization, and evaluation of its possible application in the diagnosis of histoplasmosis

The goal of the present work was to develop a novel reagent with potential for histoplasmosis diagnosis. For this purpose, the genetic sequence of the 100 kDa protein of Histoplasma capsulatum (Hcp100) was cloned and expressed as a secretory protein in Pichia pastoris. After optimizing the culture conditions and purifying by immobilized metal ion affinity chromatography, the highest yield of Hcp100 reached approximately 1.3 mg/l with > 90% purity in shake flasks using basal salt medium supplemented with casamino acids after 72 h of methanol induction. To investigate its potential for diagnosis, its detection in urine samples using specific polyclonal antibodies as reagent was evaluated by dot blot in 6 patients with progressive disseminated histoplasmosis (PDH), of whom all had AIDS. Antigen was detected in urine from all 6 (100%) PDH patients. Urine samples from a pool of 20 healthy individuals did not react with the anti-Hcp100 antibodies. The dot blot assay performed in this study provides preliminary data of a simple technology that can be performed in medical institutions with limited resources to facilitate the rapid diagnosis of histoplasmosis, particularly the disseminated forms. Hence, use of these assays may provide a rapid diagnostic tool of PDH in endemic areas for histoplasmosis where PDH-related mortality is high, hastening treatment and improving patient survival. Finally, this novel antigen and its specific antibodies may provide an alternative diagnostic reagent to the largely unknown and poorly characterized polysaccharide antigens (HPA, galactomannan, histoplasmin) frequently used in the diagnostic tests. KEY POINTS: Few antigens are used as laboratory tools for the immunodiagnosis of histoplasmosis. P. pastoris was an excellent system for recombinant Hcp100 expression. Maximum expression levels of rHcp100 were achieved in BSM with 1% casamino acids. Dot blot assays with anti-rHcp100 antisera can be successfully used for diagnosing PHD.

Chronic Pulmonary Histoplasmosis-A Scoping Literature Review

Chronic pulmonary histoplasmosis (CPH) is an uncommon manifestation of Histoplasma infection with features similar to pulmonary tuberculosis (TB). In endemic areas, it may be misdiagnosed as smear-negative pulmonary TB. Historical case series mainly from patients with presumed TB described a high frequency of cavitation and poor prognosis, likely resulting from delayed presentation. More recent reports suggest that CPH can present with nodules, lymphadenopathy, or infiltrates, with cavities being a less common feature. Emphysema is the main risk factor for cavitary CPH. CPH is therefore an umbrella term, with chronic cavitary pulmonary histoplasmosis and Histoplasma nodules being the main long-term manifestations in nonimmunocompromised individuals. Diagnosis relies on a high index of suspicion, use of fungal culture of respiratory samples, antibody testing, and compatible radiological picture. Treatment with itraconazole for at least 12 months is recommended. Morbidity from CPH results from slow progression of cavities and gradual loss of lung function, especially if not recognized and treated. Studies on the epidemiology of CPH are needed in order to improve understanding of the disease.

Role of western blot assay for the diagnosis of histoplasmosis in AIDS patients from a National Institute of Infectious Diseases in Rio de Janeiro, Brazil

BACKGROUND

Histoplasmosis is a frequent fungal infection in HIV/AIDS patients, with high morbimortality rates when diagnosis and treatment are delayed. Antibody detection, which is faster than the gold standard culture test, hastens the laboratory investigation.

OBJECTIVES

To evaluate the role of WB for antibody detection in the diagnosis of histoplasmosis among HIV/AIDS patients.

PATIENTS AND METHODS

Fifty patients with proven or probable histoplasmosis were included. Clinical, epidemiological and laboratory data were described in the same population after a review of their medical records. WB was performed using deglycosylated histoplasmin.

RESULTS

About 82% of patients were adult males and the mean age was 39.3 years. CD4⁺ T lymphocyte count less than 150 cells/mm³ was observed in 62% patients. Antibodies against Histoplasma capsulatum M antigen were detected in 62% of patients, and against both M and H antigens in 28% of individuals. Sera from 10% of patients were nonreactive. Histoplasmosis was the first opportunistic infection in 38% of the cases. Disseminated and pulmonary histoplasmosis occurred in 84% and 16% of patients, respectively. The overall mortality was 16%.

CONCLUSION

WB could be useful for the histoplasmosis diagnosis in HIV/AIDS patients because of its easefulness and good sensitivity in a population where antibody production is hampered.

Pulmonary histoplasmoma: a disguised malady

Histoplasmosis is a mycosis caused by the dimorphic fungus, Histoplasma capsulatum, which is transmitted via dust and aerosols. Lung involvement is the most common, with a varied clinical presentation. Although it is not the only source of infection, H. capsulatum is frequently found in bat guano, which is the reason why it is highly prevalent among caving practitioners. The solitary histoplasmoma of the lung is an unusual and chronic manifestation of this entity, which mimics, or at least is frequently misconstrued, as a malignancy. Almost invariably, the diagnosis of this type of histoplasmosis presentation is achieved after lung biopsy. The authors present the case of a young woman who sought medical care because of chest pain. The diagnostic work-up revealed the presence of a pulmonary nodule. She was submitted to a thoracotomy and wedge pulmonary resection. The histologic analysis rendered the diagnosis of histoplasmoma. This report aims to call attention to this diagnosis as the differential diagnosis of a pulmonary nodule.

Association between AKT rs2494752 single nucleotide polymorphism and the risk of metastasis in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common types of human tumors, which is characterized by high morbidity and mortality rates. AKT1 transcriptional activity is implicated in HCC initiation and development. In the present study, the effects of rs2494752 single nucleotide polymorphism (SNP) on AKT1 transcriptional activity in the progression of HCC cells were investigated. A case-control study was analyzed in 1,056 HCC patients and 1,080 healthy individuals using the PCR assay method. Results indicated AKT1 expression levels were up-regulated in HCC tissue compared to adjacent normal tissues. Furthermore, a higher frequency of AKT rs2494752 AG and AA genotypes were observed in HCC cases (P=0.0046). Gene polymorphism identified C and T alleles were frequency in HCC patients compared to healthy individuals. Individuals harboring AKT rs2494752 AG/AA genotype had a vital increased susceptibility to HCC in the dominant model (P=0.0028). In addition, AKT1 rs2494752 GG genotype showed an increasing of AKT1 promoter activity determined by the luciferase assay. Furthermore, it was demonstrated that AKT1 rs2494752 GG and C polymorphism was more aggressive than other AKT1 rs2494752 cancer cells. Moreover, AKT1 rs2494752 GG markedly increased rates of response to NCT chemotherapy. Additionally, results revealed that AKT1 rs2494752 GG and C increased the risk factors of HCC. In conclusion, these results indicate that AKT1 rs2494752 polymorphisms may be regarded as a candidate gene in assessing the susceptibility, metastasis and responses to chemotherapy in the progression of hepatocellular carcinoma.

Human fibroblast growth factor-21 serves as a predictor and prognostic factor in patients with hepatitis B cirrhosis combined with adrenal insufficiency

Hepatitis B cirrhosis is caused by liver cell necrosis, residual liver cell nodular regeneration, connective tissue hyperplasia and fiber formation, which frequently leads to adrenal insufficiency. Previous reports have demonstrated that human fibroblast growth factor (hFGF)-21 is a multifunctional protein that exhibits potential therapeutic value for metabolic diseases. The present study investigated the diagnostic value of hFGF-21 and analyzed the potential molecular mechanism in the progression of hepatitis B cirrhosis combined with adrenal insufficiency. Characteristics of cellular immunity and humoral immunity were analyzed in patients with hepatitis B cirrhosis combined with adrenal insufficiency (PhbA). Results demonstrated that expression levels of hFGF-21 were downregulated in plasma and liver cells isolated from clinical specimens. Plasma concentration levels of hFGF-21 were upregulated in prognostic PhbA. In vitro assays indicated that hFGF-21 treatment decreased the continuous deposition of extracellular matrix and reactive oxygen species in liver cells isolated from clinical specimens. Results also demonstrated that hFGF-21 treatment downregulated inflammatory cytokines. It was observed that hFGF-21 treatment downregulated nuclear factor (NF)-κB and Kruppel-like factor 6. Notably, transforming growth factor (TGF)-β, platelet-derived growth factor and epidermal growth factor levels were improved by hFGF-21 treatment. In conclusion, these results indicated that hFGF-21 inhibits inflammation by regulation of the NF-κB-mediated TGF-β signaling pathway, which may serve as a predictor and prognostic factor in PhbA.

Costus root granules improve ulcerative colitis through regulation of TGF-β mediation of the PI3K/AKT signaling pathway

Ulcerative colitis is a chronic nonspecific inflammatory disease that occurs in the colon and rectum. Costus root is a type of traditional Chinese medicine that exhibits antibacterial properties and serves an inhibitory role in the regeneration of gut bacteria. However, the molecular mechanisms underlying Costus root-mediated improvements in ulcerative colitis remain unclear. A complex formula of Costus root granules was created and investigated in the present study for its therapeutic effects in a rat model of ulcerative colitis. Ingredient dissolution into a traditional water decoction was used as a control. The potential mechanism mediated by Costus root granules was also analyzed in colonic epithelial cells isolated from the experimental rats. The results of the present study demonstrated that Costus root granule treatment inhibited inflammation in colonic tissue. Costus root granule treatment also suppressed the apoptosis of colonic epithelial cells isolated from the rat model of ulcerative colitis. Analyses of the underlying mechanisms of these effects indicated that the administration of Costus root granules increased transforming growth factor β expression, which activated the phosphoinositide 3-kinase/RAC-α serine/threonine-protein kinase signaling pathway in colonic epithelial cells. Notably, the administration of Costus root granules improved stomachache, diarrhea and hematochezia in and increased the body weight of, the ulcerative colitis rats. In conclusion, these results indicate that Costus root granules markedly ameliorate inflammation of the colonic epithelium, decrease the apoptosis of colonic epithelial cells and improve colonic function, which suggests that Costus root granules are an efficient agent for the treatment of ulcerative colitis.

Comparison of diagnostic methods to detect Histoplasma capsulatum in serum and blood samples from AIDS patients

BACKGROUND

Although early and rapid detection of histoplasmosis is essential to prevent morbidity and mortality, few diagnostic tools are available in resource-limited areas, especially where it is endemic and HIV/AIDS is also epidemic. Thus, we compared conventional and molecular methods to detect Histoplasma capsulatum in sera and blood from HIV/AIDS patients.

METHODOLOGY

We collected a total of 40 samples from control volunteers and patients suspected of histoplasmosis, some of whom were also infected with other pathogens. Samples were then analyzed by mycological, serological, and molecular methods, and stratified as histoplasmostic with (group I) or without AIDS (group II), uninfected (group III), and infected with HIV and other pathogens only (group IV). All patients were receiving treatment for histoplasmosis and other infections at the time of sample collection.

RESULTS

Comparison of conventional methods with nested PCR using primers against H. capsulatum 18S rRNA (HC18S), 5.8S rRNA ITS (HC5.8S-ITS), and a 100 kDa protein (HC100) revealed that sensitivity against sera was highest for PCR with HC5.8S-ITS, followed by immunoblotting, double immunodiffusion, PCR with HC18S, and PCR with HC100. Specificity was equally high for double immunodiffusion, immunoblotting and PCR with HC100, followed for PCR with HC18S and HC5.8-ITS. Against blood, sensitivity was highest for PCR with HC5.8S-ITS, followed by PCR with HC18S, Giemsa staining, and PCR with HC100. Specificity was highest for Giemsa staining and PCR with HC100, followed by PCR with HC18S and HC5.8S-ITS. PCR was less efficient in patients with immunodeficiency due to HIV/AIDS and/or related diseases.

CONCLUSION

Molecular techniques may detect histoplasmosis even in cases with negative serology and mycology, potentially enabling early diagnosis.

Histoplasmosis in Africa: An emerging or a neglected disease?

Histoplasmosis in Africa has markedly increased since the advent of the HIV/AIDS epidemic but is under-recognised. Pulmonary histoplasmosis may be misdiagnosed as tuberculosis (TB). In the last six decades (1952-2017), 470 cases of histoplasmosis have been reported. HIV-infected patients accounted for 38% (178) of the cases. West Africa had the highest number of recorded cases with 179; the majority (162 cases) were caused by Histoplasma capsulatum var. dubuosii (Hcd). From the Southern African region, 150 cases have been reported, and the majority (119) were caused by H. capsulatum var. capsulatum (Hcc). There have been 12 histoplasmin skin test surveys with rates of 0% to 35% positivity. Most cases of Hcd presented as localised lesions in immunocompetent persons; however, it was disseminated in AIDS patients. Rapid diagnosis of histoplasmosis in Africa is only currently possible using microscopy; antigen testing and PCR are not available in most of Africa. Treatment requires amphotericin B and itraconazole, both of which are not licensed or available in several parts of Africa.

Fast protocol for the production of Histoplasma capsulatum antigens for antibody detection in the immunodiagnosis of histoplasmosis

BACKGROUND

Current methods for the production of Histoplasma capsulatum antigens are problematic in terms of standardization, specificity, stability, repeatability and reproducibility.

AIMS

In this study, we sought to optimize the methodology for producing H. capsulatum antigens, and to evaluate its applicability.

METHODS

Antigenic preparations obtained from 12 H. capsulatum isolates were evaluated by double immunodiffusion and immunoblotting assays against homologous and heterologous sera.

RESULTS

The evaluated and optimized protocol allowed a more stable production, as well as repeatable, reproducible, with shorter culture time and less costly. By double immunodiffusion and immunoblotting assays, the best pattern of reactivity was observed for antigens obtained with 33 days of culture from the isolates 200 and 406 against the M antigen and for the isolate 200 with 15 days against H antigen. The SDS-PAGE presented antigenic components of molecular masses between 17 and 119kDa. The immunoblotting sensitivity was 95.5% and 100% with histoplasmosis sera from ill patients and sera from H. capsulatum infected but otherwise healthy patients, respectively, to the antigen derived from isolates 200 and 406.

CONCLUSIONS

We suggest the employment of the antigen from isolate 200, with 15 or 30 days of culture, in the double immunodiffusion and immunoblotting assays due to its good ability to discriminate both sera from patients with histoplasmosis illness and histoplasmosis infection, in addition to its high specificity against heterologous sera.