10 5 The rubella virus stimulates the production of antibodies in humans but usually causes only mild infections. However, infection of pregnant women can cause serious problems for the developing fetus. *(a) Antibodies can be divided into five classes. The table gives some information about these classes of antibody. Information Class of antibody IgM IgA IgG IgD IgE Shape Number of antigen binding sites 10 4 2 2 2 Can cross the placenta no no yes no no Other details secreted into the blood secreted into mucus, tears, saliva, colostrum1 secreted into the blood attached to the surface of B cells involved in allergy and parasitic infections 1 Colostrum is the first type of milk produced by the mother following birth. The graph shows the levels of three of these classes of antibody produced in response to infection with the rubella virus. Levels of antibody 0 1 2 3 4 IgM IgG IgA Time after infection/months 11 Turn over Analyse the information in the table and the graph to assess the role of these five classes of antibody in the immune response to the rubella virus. 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Explain the importance of vaccinating as many people as possible against rubella. 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(Total for Question 5 = 8 marks)