Question

How do retroviruses impact western blot for HIV

How does rheumatoid factor influence the outcome of a patients HIV IgG ELISA

Answer 1

Answer 1 - The Western blot assay is a method in which individual proteins of an HIV-1 lysate are separated according to size by polyacrylamide gel electrophoresis. The viral proteins are then transferred onto nitrocellulose paper and reacted with the patient's serum. Any HIV antibody from the patient's serum is detected by an antihuman immunoglobulin G (IgG) antibody conjugated with an enzyme that in the presence of substrate will produce a colored band. Positive and negative control serum specimens are run simultaneously to allow identification of viral proteins.Western blot interpretation is not sensitive enough for public health or clinical practice.

The overall sensitivity and specificity of the Western blot for detection of antibodies to the various viral proteins are high. The currently licensed Du Pont Western blot test specifies that the test result should be interpreted as positive only when the detected bands include proteins bands of p24 and p31, and gp41 or gp120/160. Conversely, a negative Du Pont Western blot test result requires the absence of any and all bands--not just viral-bands. All other patterns are regarded as indeterminate. This interpretation scheme maximizes the specificity of the assay and is mainly intended for use with samples from persons, such as blood donors, for whom there is usually little clinical or virologic information available. The criteria are not ideal for all situations, especially the testing of persons at increased risk for HIV infection, or with symptoms suggestive of this infection.

Answer 2 - The main cause  of false positive results  is because the test has detected antibodies, but they are not antibodies to HIV – they are antibodies to another substance or infection, here rheumatoid factor. Thus it influences between the two diseases. The antibody titers of rheumatoid factors (RF) including RF-IgG, RF-IgM, RF-IgA, and CCP-IgG are analyzed by ELISA and thus the results may be false respectively.