Covid-19 Antibodies

Immunoglobulin M (IgM) is the first class of antibodies produced during the humoral immune response. Thus, specific antibodies of the IgM class are diagnostic of recent (or chronic) infection. The IgM class antibodies are also the first immunoglobulin class to be found in the fetus as it develops immunological capability in the second half of pregnancy. Since IgM does not cross the placenta from mother to fetus, the presence of IgM against a particular virus in a newborn is indicative of intrauterine viral infection.

Detecting IgM antibodies specific to Covid-19 proteins could therefore be used as a diagnostic tool to screen populations for recent Covid-19 infection. In such conditions, a high-affinity antibody specific to human IgM would be needed to detect the IgM antibodies specific to the viral proteins. For the test to be applied in Africa, where access to screening kits and equipment is sometimes difficult and costly, the anti-(human IgM) antibody should ideally be produced locally. Unfortunately, full-length monoclonal antibodies (mAb) produced in mammalian cells are unrealistic in areas where tissue culture facilities may be difficult and costly to maintain. As an alternative, the expression of a small version of the antibody-binding region - a so-called single-chain variable fragment (scFv) - in bacteria could be an attractive and cheap option in these countries, as they are easier to mass produce, especially where recombinant enzymes for PCR screening are produced locally.

We are using phage display technology to isolate high-affinity scFv antibodies that specifically recognise human IgM. Antibody phage display is based on genetic engineering of bacteriophages and repeated rounds of antigen-guided selection and phage propagation. It is one of the most effective molecular diversity technologies currently available and allows in vitro selection of scFvs of virtually any required specificity. Because the whole process, including mass production, is carried out in bacteria, the technology greatly facilitates the recombinant production of reagents for use in research, pharmaceutical chemistry and clinical diagnostics.

Author: Dr Samir Hamaia