Detection of IgG, IgA, IgM and IgE antibodies in invasive amoebiasis in endemic areas

Evaluation of total immunoglobulin G and subclass antibodies in an enzyme-linked immunosorbent assay for serodiagnosis of human amebic liver abscess

Background

Amebic liver abscess (ALA) caused by Entamoeba histolytica is usually diagnosed based on its clinical symptoms, medical imaging abnormalities of the liver, and serological tests, the most common being the enzyme-linked immunosorbent assay (ELISA). For more than three decades, no investigation has evaluated the diagnostic performance of immunoglobulin G (IgG) subclasses in the serodiagnosis of ALA. Herein, we assessed the efficiencies of anti-amebic IgG and IgG subclasses for diagnosing ALA.

Methods

A serological ELISA-based test was performed to assess its diagnostic performance using a total of 330 serum samples from ALA patients (n = 14), healthy individuals (n = 40), and patients with other diseases (n = 276).

Results

ELISA targeting the total IgG antibody to E. histolytica antigen exhibited 100% sensitivity 95% CI [76.8-100.0] and 97.8% specificity 95% CI [95.5-99.1], whereas the assay targeting IgG1 showed the same sensitivity (100% 95% CI [76.8-100.0]) and a slightly higher specificity (99.1% 95% CI [97.3-99.8]). The other IgG subclasses (IgG2, IgG3, and IgG4) displayed a lower sensitivity and specificity. The sensitivity and specificity did not significantly differ between tests measuring total IgG and IgG1 (Exact McNemar's test; p > 0.05), with a concordance of 98.2%, represented by a Cohen's kappa of 0.83 (p < 0.001), indicating almost perfect agreement.

Conclusion

ELISA targeting IgG1 can provide valuable information to clinicians in differentiating ALA from other parasitic diseases, cancers, cirrhosis, and viral hepatitis. However, enzyme-conjugated anti-human total IgG is cheaper than anti-human IgG subclasses. Therefore, we suggest that total IgG-based ELISA is sufficient for the routine serodiagnosis of human ALA and possibly other clinical manifestations of invasive amebiasis.

Profiles of Entamoeba histolytica-specific immunoglobulins in human sera

OBJECTIVE

To determine the profiles of anti-Entamoeba histolytica (E. histolytica) IgA, IgG, and IgM in sera of diarrheic and non-diarrheic individuals and partially characterize target antigens.

METHODS

Serum samples from thirty diarrheic and thirty non-diarrheic individuals were subjected to IgA, IgG, and IgM profiling through enzyme-linked immunosorbent assay (ELISA), flow cytometry, and immunoblot.

RESULTS

ELISA titer results showed that both diarrheic and non-diarrheic individuals possess high levels of E. histolytica-specific IgG compared to IgA and IgM. Flow cytometry data showed that diarrheic serum samples had higher mean reaction percentages against E. histolytica cells compared to non-diarrheic samples. Immunoreactive E. histolytica proteins with molecular weights ranging between 7 kDa and 292 kDa were recognized by diarrheic serum IgG, and 170 kDa and 250 kDa by non-diarrheic serum IgG.

CONCLUSIONS

Our findings suggest that serum anti-E. histolytica IgG, compared with serum anti-E. histolytica IgA and IgM responses, was generally high in both diarrheic and non-diarrheic sera, indicating a past exposure to the organism both in symptomatic patients as well as in asymptomatic carriers, respectively. In addition, serum IgG from diarrheic and non-diarrheic patients were able to detect immunogenic E. histolytica proteins.

Clinical significance of enteric protozoa in the immunosuppressed human population

Globally, the number of immunosuppressed people increases each year, with the human immunodeficiency virus (HIV) pandemic continuing to spread unabated in many parts of the world. Immunosuppression may also occur in malnourished persons, patients undergoing chemotherapy for malignancy, and those receiving immunosuppressive therapy. Components of the immune system can be functionally or genetically abnormal as a result of acquired (e.g., caused by HIV infection, lymphoma, or high-dose steroids or other immunosuppressive medications) or congenital illnesses, with more than 120 congenital immunodeficiencies described to date that either affect humoral immunity or compromise T-cell function. All individuals affected by immunosuppression are at risk of infection by opportunistic parasites (such as the microsporidia) as well as those more commonly associated with gastrointestinal disease (such as Giardia). The outcome of infection by enteric protozoan parasites is dependent on absolute CD4(+) cell counts, with lower counts being associated with more severe disease, more atypical disease, and a greater risk of disseminated disease. This review summarizes our current state of knowledge on the significance of enteric parasitic protozoa as a cause of disease in immunosuppressed persons and also provides guidance on recent advances in diagnosis and therapy for the control of these important parasites.

Recombinant antigen-based avidin-biotin microtiter enzyme-linked immunosorbent assay for serodiagnosis of invasive amebiasis

An immunoscreening approach was used to isolate a strongly positive cDNA clone from an Entamoeba histolytica HK-9 cDNA expression library in the phage vector lambda ZAP-II. The 1.85-kb cDNA insert was found to be truncated and encoded the cysteine-rich, immunodominant domain of the antigenic 170-kDa subunit of the amebal galactose-N-acetylgalactosamine binding lectin. This domain was expressed as a glutathione S-transferase fusion protein in Escherichia coli. Inclusion bodies of the recombinant protein were solubilized with Sarkosyl, and the protein was enriched from the crude bacterial extract by thiol-affinity chromatography. The recombinant protein was used to develop a rapid, sensitive, and specific avidin-biotin microtiter enzyme-linked immunosorbent assay (ELISA) for invasive amebiasis. Sera from 38 individuals suffering from invasive amebiasis, 12 individuals with noninvasive amebiasis, 44 individuals with other infections, and 27 healthy subjects were screened by the recombinant antigen-based ELISA. The sensitivity and specificity of the assay were 90.4 and 94.3%, respectively, which correlated well with those of an ELISA developed with crude amebal antigen (r = 0.94; P < 0.0001), as well as with those of a commercially available serodiagnostic ELISA (r = 0.92; P < 0.0001). Thus, the bacterially expressed recombinant lectin can replace the crude amebal extract as an antigen in the serodiagnosis of invasive amebiasis by using avidin-biotin microtiter ELISA.

Diagnostic tests for amoebic liver abscess: comparison of enzyme-linked immunosorbent assay (ELISA) and counterimmunoelectrophoresis (CIE)

The liver abscess is the most frequent extraintestinal complication of intestinal amoebiasis: its diagnosis is suggested by the clinical picture but it must be confirmed by paraclinic tests. Themost stringent diagnosis requires identification of E. histolytica. But this is possible only in a few cases. Serological tests greatly improve the diagnosis of this severe complication of amoebiasis. We compared the Enzyme Linfed Immunosorbent Assay and the Counterimmunoelectrophoresis techniques. Both techniques were used to detect amoebic antibodies in 50 control patients, 30 patients with liver abscess and 30 patients with intestinal amoebiasis. All the sera from control patients gave negative results in both techniques. When analysing the sera from patients with intestinal amoebiasis, 10% of them were positive by ELISA but non by CIE. The sera of patients with liver abscess, we found that 90% were positive by the ELISA method and 66.6% by the CIE technique. In patients with amoebic liver abscess, the results showed that the ELISA was more sensitive than the CIE, as it presented a higher sensitivity (100%) than that of the CIE technique (66%).