A novel monoclonal antibody recognizing beta(1-3) glucans in intact cells of Candida and Cryptococcus

A novel enzyme immunoassay for the measurement of plasma (1 → 3)-β-D-glucan levels

The presence of (1 → 3)-β-D-glucan in human plasma is a marker for fungal infections. Currently, the Limulus amebocyte lysate (LAL)-based assay is widely used for the quantification of plasma (1 → 3)-β-D-glucan. However, it has limitations in clinical use, such as an unstable supply of natural resources, complicated manufacturing process, and low-throughput of the reagents. Alternative assays exploiting specific antibodies against (1 → 3)-β-D-glucan have been developed to overcome these challenges. However, these methods are associated with low sensitivity and poorly correlate with the data obtained by the LAL-based assay. The aim of this study is to develop a novel enzyme immunoassay that is as sensitive and accurate in determining plasma (1 → 3)-β-D-glucan levels as compared to that obtained with the LAL-based assay. We generated specific monoclonal antibodies against (1 → 3)-β-D-glucan that recognizes four-unit glucose oligomers with (1 → 3)-β-D-linkages, and constructed a sandwich enzyme-linked immunosorbent assay (ELISA) using these antibodies. The newly developed ELISA showed proportional increase in absorbance with the volume of (1 → 3)-β-D-glucan added. The limit of detection of the assay was 4 pg/ml of plasma (1 → 3)-β-D-glucan that was equivalent to the LAL-based assay and the working range was 4-500 pg/ml. The intra-assay coefficient of variation was 2.2-5.4% using three different concentrations of plasma samples. We observed strong correlation (R = 0.941, slope = 0.986) between the measurements obtained by our ELISA and Fungitec G test ES Nissui, a commonly used LAL-based assay, using 26 types of plasma samples. This could be attributed to the epitopes of the antibodies. Both antibodies could inhibit the LAL-based assay, suggesting that the antibodies recognize the identical regions in β-D-glucan, thereby inactivating factor G, an initiation zymogen for coagulation cascade, in the LAL-based assay. Thus, the ELISA developed in this study can detect fungal infections in clinical settings with similar efficiency as the LAL-based assay. This assay is characterized by good performance, stable supply of materials, and simple manufacturing process and is more suitable for the high-throughput diagnosis of fungal infections.

Cell Wall Modifications in Giant Cells Induced by the Plant Parasitic Nematode Meloidogyne incognita in Wild-Type (Col-0) and the fra2 Arabidopsis thaliana Katanin Mutant

Meloidogyne incognita is a root knot nematode (RKN) species which is among the most notoriously unmanageable crop pests with a wide host range. It inhabits plants and induces unique feeding site structures within host roots, known as giant cells (GCs). The cell walls of the GCs undergo the process of both thickening and loosening to allow expansion and finally support nutrient uptake by the nematode. In this study, a comparative in situ analysis of cell wall polysaccharides in the GCs of wild-type Col-0 and the microtubule-defective fra2 katanin mutant, both infected with M. incognita has been carried out. The fra2 mutant had an increased infection rate. Moreover, fra2 roots exhibited a differential pectin and hemicellulose distribution when compared to Col-0 probably mirroring the fra2 root developmental defects. Features of fra2 GC walls include the presence of high-esterified pectic homogalacturonan and pectic arabinan, possibly to compensate for the reduced levels of callose, which was omnipresent in GCs of Col-0. Katanin severing of microtubules seems important in plant defense against M. incognita, with the nematode, however, to be nonchalant about this "katanin deficiency" and eventually induce the necessary GC cell wall modifications to establish a feeding site.

Association Between Plasma Antibody Responses and Risk for Cryptococcus-Associated Immune Reconstitution Inflammatory Syndrome

Background

Initiation of antiretroviral therapy (ART) in human immunodeficiency virus (HIV)-infected individuals with cryptococcal meningitis places them at risk for Cryptococcus-associated immune reconstitution inflammatory syndrome (C-IRIS). The relationship between antibody immunity and C-IRIS risk has not been investigated.

Methods

We compared plasma levels of immunoglobulins, C. neoformans glucuronoxylomannan (GXM) capsule-specific and laminarin (Lam)-binding IgM and IgG, and percentages of peripheral blood total and memory B cells between 27 HIV-infected patients with CM who developed C-IRIS and 63 who did not, and evaluated associations of these parameters with risk of C-IRIS.

Results

Prior to initiation of ART, plasma IgM, Lam-binding IgM (Lam-IgM), Lam-IgG, and GXM-IgM levels were significantly lower in patients who developed C-IRIS than those who did not. Multivariate analysis revealed significant inverse associations between C-IRIS and IgM (P = .0003), Lam-IgM (P = .0005), Lam-IgG (P = .002), and GXM-IgM (P = .002) independent of age, sex, HIV viral load, CD4+ T-cell count, and cerebrospinal fluid fungal burden. There were no associations between C-IRIS and total or memory B cells.

Discussion

Antibody profiles that include plasma IgM, Lam-IgM, Lam-IgG, and/or GXM-IgM may have value in furthering our understanding of C-IRIS pathogenesis and hold promise as candidate biomarkers of C-IRIS risk.

Antibody Responses in HIV-Infected Patients With Advanced Immunosuppression and Asymptomatic Cryptococcal Antigenemia

Background

There are no host biomarkers of risk for HIV-associated cryptococcal meningitis (CM) except CD4+ T-cell deficiency. At present, serum cryptococcal antigen (CrAg) screening of those with CD4 <100 cells/µL is used to identify persons at risk for HIV-associated CM. We determined if plasma antibody profiles could discriminate CrAg+ from CrAg- patients.

Methods

We performed serological analyses of 237 HIV-infected asymptomatic Zimbabwean patients with CD4 <100 cells/µL; 125 CrAg- and CrAg+ but cerebrospinal fluid CrAg- by CrAg lateral flow assay. We measured plasma immunoglobulin M (IgM), immunoglobulin G (IgG) 1, and IgG2 concentrations by Luminex, and titers of Cryptococcus neoformans (Cn) glucuronoxylomannan (GXM) polysaccharide and naturally occurring Laminarin (natural Lam, a β-(1–3)-glucan linked polysaccharide)-binding IgM and IgG by enzyme-linked immunosorbent assay.

Results

GXM-IgG, -IgM, and -IgG2 levels were significantly higher in CrAg+ patients, whereas natural Lam-IgM and Lam-IgG were higher in CrAg- patients before and after adjustment for age, sex, and CD4 T-cell count, despite overlap of values. To address this variability and better discriminate the groups, we used Akaike Information Criteria to select variables that independently predicted CrAg+ status and included them in a receiver operating characteristic curve to predict CrAg status. By inclusion of CD4, GXM-IgG, GXM-IgM, and Lam-IgG, -IgG2, and -IgM, this model had an 80.4% probability (95% confidence interval, 0.75–0.86) of predicting CrAg+ status.

Conclusions

Statistical models that include multiple serological variables may improve the identification of patients at risk for CM and inform new directions in research on the complex role that antibodies may play in resistance and susceptibility to CM.

Candida infections and their prevention

Infections caused by Candida species have been increased dramatically worldwide due to the increase in immunocompromised patients. For the prevention and cure of candidiasis, several strategies have been adopted at clinical level. Candida infected patients are commonly treated with a variety of antifungal drugs such as fluconazole, amphotericin B, nystatin, and flucytosine. Moreover, early detection and speciation of the fungal agents will play a crucial role for administering appropriate drugs for antifungal therapy. Many modern technologies like MALDI-TOF-MS, real-time PCR, and DNA microarray are being applied for accurate and fast detection of the strains. However, during prolonged use of these drugs, many fungal pathogens become resistant and antifungal therapy suffers. In this regard, combination of two or more antifungal drugs is thought to be an alternative to counter the rising drug resistance. Also, many inhibitors of efflux pumps have been designed and tested in different models to effectively treat candidiasis. However, most of the synthetic drugs have side effects and biomedicines like antibodies and polysaccharide-peptide conjugates could be better alternatives and safe options to prevent and cure the diseases. Furthermore, availability of genome sequences of Candida   albicans and other non-albicans strains has made it feasible to analyze the genes for their roles in adherence, penetration, and establishment of diseases. Understanding the biology of Candida species by applying different modern and advanced technology will definitely help us in preventing and curing the diseases caused by fungal pathogens.

CD4+ T cells mediate the protective effect of the recombinant Asp f3-based anti-aspergillosis vaccine

The mortality and morbidity caused by invasive aspergillosis present a major obstacle to the successful treatment of blood cancers with hematopoietic cell transplants. Patients who receive hematopoietic cell transplants are usually immunosuppressed for extended periods, and infection with the ubiquitous mold Aspergillus fumigatus is responsible for most cases of aspergillosis. Previously, we demonstrated that vaccination with recombinant forms of the A. fumigatus protein Asp f3 protected cortisone acetate-immunosuppressed mice from experimentally induced pulmonary aspergillosis. Here, we investigated the vaccine's protective mechanism and evaluated in particular the roles of antibodies and T cells. After vaccination, Asp f3-specific preinfection IgG titers did not significantly differ between surviving and nonsurviving mice, and passive transfer of anti-Asp f3 antibodies did not protect immunosuppressed recipients from aspergillosis. We experimentally confirmed Asp f3's predicted peroxisomal localization in A. fumigatus hyphae. We found that fungal Asp f3 is inaccessible to antibodies, unless both cell walls and membranes have been permeabilized. Antibody-induced depletion of CD4+ T cells reduced the survival of recombinant Asp f3 (rAsp f3)-vaccinated mice to nonimmune levels, and transplantation of purified CD4+ T cells from rAsp f3-vaccinated mice into nonimmunized recipients transferred antifungal protection. In addition, residues 60 to 79 and 75 to 94 of Asp f3 contain epitopes that induce proliferation of T cells from vaccinated survivors. Vaccine-primed CD4+ T cells are not expected to clear the fungal pathogen directly; however, they may locally activate immunosuppressed phagocytes that elicit the antifungal effect.

Potential of anti-Candida antibodies in immunoprophylaxis

The need for new options for the treatment of invasive candidiasis has fuelled the use of antibodies in combination with conventional antifungal therapy. After a long period of time in which antibodies were considered irrelevant in the resistance against invasive candidiasis, it was demonstrated that a number of antibodies or their engineered derivatives directed against Candida albicans cell-wall polysaccharides and glycopeptides, as well as against some protein epitopes, confer protection against invasive candidiasis. This has confirmed this approach as a new strategy for the prophylaxis of invasive candidiasis. Of particular interest is Mycograb, a human recombinant monoclonal antibody that inhibits heat shock protein 90, and has been administrated in combination with lipid-associated amphotericin B to patients with invasive candidiasis, and the fungicidal anti-beta-glucan antibodies induced by the glycoconjugate vaccine composed of a beta-glucan polysaccharide conjugated with the diphtheria toxoid CRM 197. However, despite the promising data obtained in vitro and in animal models, at present there is very little clinical experience on the use of antibodies in Candida immunoprophylaxis.

Real-time polymerase chain reaction detection of Cryptococcus neoformans and Cryptococcus gattii in human samples

We report a TaqMan real-time polymerase chain reaction (PCR) protocol for diagnosing cryptococcosis. Specificity was tested with 33 fungal strains. The 7 clinical samples found positive by culture also tested positive by real-time PCR. No false negatives were found among the 94 clinical samples that were negative by culture for Cryptococcus spp. The sensitivity threshold was about 10 plasmid copies per assay.