Avidity of antibodies -What is meant by high avidity IgM antibodies??

 

The presence of high avidity antibodies, which develop by about three months after infection, provides evidence of remote infection.. What is meant by IgM positivity was is in this case? IgM reactivity It is important to distinguish IgM reactivity caused by primary infection from that caused by IgM persistence or cross-reactivity with other antigens, especially in pregnant women.

The measurement of rubella IgG antibody avidity can be used to distinguish between recent infection and remote rubella infection.

 

Antibody avidity (the overall strength of binding between the antigen and antibody) increases with time; this is known as maturation of the immune response. As the immune response matures, low avidity antibodies are replaced with high avidity antibodies. These avidity differences can be detected by using protein denaturants such as diethylamine (DEA) in the washing step of an enzyme-linked immunoassay (EIA) for rubella IgG. In acute rubella virus infections, specific, low-avidity IgG lasts for up to three months after appearance of the IgG response. The presence of high avidity antibodies, which develop by about three months after infection, provides evidence of remote infection. The cut-off between low and high avidities has to be established by using standardized sera and a particular EIA kit.

For pregnant women, avidity testing is most useful in early pregnancy to help rule out a rubella infection in the first trimester, when the risk of congenital defects due to rubella is highest. It is not as useful in late pregnancy because avidity will be high by the third trimester if infection occurred in the first trimester