In Fact , to understand the concept of "Avidity" you have to be aware of the concept of "Affinity" first !
Affinity describes the strength of a single interaction between two molecules to each other,or a receptor to an enzyme or a hormone, when it's said that a certain receptor has a stronger affinity to a certain molecule , so it indicates a stronger bonding and more energy required to reduce or break their interaction.
Avidity is described as the accumulated strength of multiple affinities of individual non-covalent binding interactions !
Forget about definitions ! the best application that would demonstrate the difference is to understand IgM function versus other Immunoglobulins, IgM has 10 binding sites for certain antigen , but each binding site has a weak bonding to this antigen, in contrast IgG has only two binding sites for antigens but much more stronger and specific binding with target antigen , therefore, IgM is said to have a High Avidity but a Low Affinity, while IgG molecules are said to have Low Avidity, but High Affinity.
the best application for these concepts is to know the value and importance of Avidity tests in TORCHES infection screening particularly for Toxoplasmosis , CMV and Rubella infections, if serology would show presence of both IgM and IgG antibodies against certain antigen , Avidity test is then used to determine risk of fetal infection, High avidity excludes possibility of transmission of infections while low Avidity suggests the possibility of transmission of the disease.
Affinity describes the strength of a single interaction between two molecules to each other,or a receptor to an enzyme or a hormone, when it's said that a certain receptor has a stronger affinity to a certain molecule , so it indicates a stronger bonding and more energy required to reduce or break their interaction.
Avidity is described as the accumulated strength of multiple affinities of individual non-covalent binding interactions !
Forget about definitions ! the best application that would demonstrate the difference is to understand IgM function versus other Immunoglobulins, IgM has 10 binding sites for certain antigen , but each binding site has a weak bonding to this antigen, in contrast IgG has only two binding sites for antigens but much more stronger and specific binding with target antigen , therefore, IgM is said to have a High Avidity but a Low Affinity, while IgG molecules are said to have Low Avidity, but High Affinity.
the best application for these concepts is to know the value and importance of Avidity tests in TORCHES infection screening particularly for Toxoplasmosis , CMV and Rubella infections, if serology would show presence of both IgM and IgG antibodies against certain antigen , Avidity test is then used to determine risk of fetal infection, High avidity excludes possibility of transmission of infections while low Avidity suggests the possibility of transmission of the disease.
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