Enzyme Immunoassay for the Determination of H. pylori IgA Level in Human Serum
Introduction
Helicobacter pylori (H. pylori) is a Gram-negative bacterium residing in the gastric mucosa. It is found in 95-98% of patients with duodenal ulcers and 60-90% of those with gastric ulcers (Peterson, 1991). The infection rate varies based on diagnostic methods, including bacteriological, histological, and serological tests, indicating that nearly 90% of symptomatic patients are affected, while about 50% of older adults (>50 years) may carry the bacteria asymptomatically (McGuigan, 1988). Studies have demonstrated that eradicating H. pylori through antimicrobial therapy correlates with symptom resolution and disease cure (Podolsky, 1989).
Clinical Significance
H. pylori infection is a major risk factor for gastritis, peptic ulcer disease, and gastric cancer (Perez & Blaser, 1991). The immune response to the infection includes the production of specific antibodies such as IgG, IgM, and IgA. The presence of H. pylori-specific IgA in the serum can indicate an active infection or colonization, providing valuable information for diagnosis and monitoring treatment efficacy. ELISA-based detection of IgA serves as a non-invasive diagnostic tool, especially in patients where biopsy-based methods are not feasible.
Diagnostic Methods
Patients with gastrointestinal symptoms suggestive of H. pylori infection can be diagnosed using:
- Invasive Techniques – These include biopsy followed by culture, histological examination, or direct urease activity detection.
- Non-Invasive Techniques – These include urea breath tests and serological methods, such as ELISA.
Biopsy-based tests are prone to errors due to sampling inconsistencies and bacterial contamination, making serological assays like the H. pylori IgA ELISA a reliable alternative.
Test Principle
The H. pylori IgA ELISA is an indirect enzyme-linked immunosorbent assay (ELISA). Microtiter wells are coated with H. pylori antigens, and diluted serum samples are incubated with these antigen-coated wells. If specific IgA antibodies are present, they bind to the immobilized antigens. After washing, an anti-human IgA antibody conjugated to horseradish peroxidase (HRP) is added, followed by a substrate reaction that generates a color change. The intensity of the color, measured spectrophotometrically at 450 nm, is directly proportional to the concentration of H. pylori IgA in the sample.
References
- McGuigan, J. E. (1988). Peptic ulcer and gastritis. Harrison’s Principles of Internal Medicine, 12th ed., 238, 1229-1248.
- Peterson, W. L. (1991). H. pylori and peptic ulcer disease. New England Journal of Medicine, 324, 1024-1047.
- Podolsky, I. (1989). Prevalence of H. pylori in healthy subjects and patients with peptic disease. Gastroenterology, 96(Suppl), A394.
- Perez, C. I., & Blaser, M. O. (1991). Serodiagnosis of H. pylori: Comparison of enzyme-linked immunosorbent assay. Journal of Clinical Microbiology, 29, 1635-1639.