Q. Which antigen is used in the new kits?

A. We use a whole virion extracted from the strain of virus isolated at the National Institute of Infectious Diseases Lazarus Spallanzani in Rome, in our Enzywell SARS-CoV-2 IgG, IgM and IgA kits. The extract is cultivated on purified and inactivated REAL cells which ensures that the antigen used in sensitization of ELISA test samples contains all viral proteins.

Q. From a clinical point of view, what is the difference between IgG, IgM and IgA in the serological diagnosis of Covid19?

A. IgMs are generally considered to be a marker of recent infection, because they are the first antibodies to be produced. The current data available on SARS-CoV-2 seems to indicate that IgMs are produced between three and 14 days after exposure to the virus.
IgA antibodies are produced through secretion into the pulmonary mucus. The purpose of these antibodies is to block SARS-CoV-2 from entering into the pulmonary system. For this reason, the presence of IgA is considered a marker of recent infection. The kinetics of appearances of IgAs reflects that of IgMs.
Finally, IgGs are the antibodies produced by the immune system in later stages of infection. They appear approximately 14 days after initial infection with SARS-CoV-2. It must, however, be remembered that since there is a great similarity between SARS-CoV-2 and other Coronaviruses circulating among the population. This can cause a cross-immune reaction in some subjects who have an immune memory for other Coronaviruses, and so IgGs may appear contemporarily to, or even precede, IgMs. Thus, the presence of IgGs can be considered a marker of previous infection, and may also confer immunity.

Q. Does the detection of IgGs performed with the Enzywell SARS-CoV-2 kit provide any indication of potential immunity to the virus?

A. Seroneutralisation is the best analytical method to show whether patient-produced IgGs are protective against the penetration of the virus into cells. In this technique a suspension of virus added to a culture of cells sensitive to the virus in the patient’s serum. If the patient's antibodies are effective in stopping the virus from getting into cells, there will be no cytopathic effect, or cellular damage. Only IgGs directed against viral proteins that bind on target cell receptors have this neutralizing effect. Like all immunological tests on the market, whether they are ELISA, immunochromatographic rapid tests or CLIA tests, our kit highlights the total IgG, and provides an indication of previous contact with the virus.

Q. What method is used?

A. The indirect ELISA method is used for the three types of antibody. The diluted serum is put to incubate in the microtitration apparatus and sensitized with the native antigen. The antibodies present in the patient's serum bind to the antigen and are revealed using a murine monoclonal antibody- specific to IgG, IgM or IgA - combined with horseradish peroxdase tracer.

Q. How do you eliminate rheumatoid interference in IgM and IgA tests?

A. Many patients with rheumatoid arthritis, as well as patients positive for hepatitis C and other infections, produce IgM or IgA immunoglobulins, which could result in diagnosing a false positive. To avoid possible rheumatoid interference diluted serums used for research of anti-SARS-CoV-2-specific IgMs and IgA are added to a receptive that removes rheumatoid factors.

Q. How long does it take to get the results?

A. It takes about 2 hours and 30 minutes to complete a 96 sample test.

Q. How are the results presented?

A. The results are presented in an index, which shows the ratio of the optical density of the serum and of the cut-off provided with the kit. For index values less than 0.8, the sample is negative, for values between 0.8 and 1.2 the result is unclear and the test should be repeated on a new sample, while for values greater than 1.2 the result is positive. The value of the index reflects the antibody stock, which is the amount of antibodies in the serum.

Q. Can kits be used for self-diagnosis?

A. NO: The kits produced by DIESSE are for professional use in vitro and should only be used by specialized personnel.