3 Antibodies
Clearly antibodies are important in protection against virus infection, but how exactly do they work? Before delving into that area, you will take a look at antibody classes because different antibody classes have different functions in immune defence.
ITQ _unit3.4.1
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Recall the names of three different antibody classes and identify a distinguishing feature of one of these classes of antibody.
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IgG, IgM and IgA are the three main classes of antibody found in serum – the liquid component of blood. IgM is the first antibody produced in a primary immune response, whereas IgG is the major antibody produced in a secondary immune response (see Figure 7).
An individual B cell initially produces an IgM antibody as its BCR. And if it is activated, it produces secreted IgM. As an immune response develops, and with help from TH2 cells, the B cell may switch to producing an IgG or IgA class of antibody. The antibody retains the same antigen-binding sites at the tips of the Y-shaped molecule, but the stem of the Y (Fc portion) is different for each class. How class-switching is effected at a molecular and cellular level is beyond the scope of this course. The key point is that IgM predominates in a primary response while IgG and IgA antibodies predominate in secondary immune responses.