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  4. The first antibody which gets formed in response to an antigen is

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Q. The first antibody which gets formed in response to an antigen is

AMUAMU 1999

Solution:

: $ IgM $ is the largest of the immunoglobulins and the first to reach the site of infection being present in the circulating fluid. When a B- lymphocyte is first stimulated by antigen $ IgM $ is the first antibody type to be produced during an immune response. $ IgM $ fixes complement and does not cross placenta. Later on $ IgG $ replaces $ IgM $ . $ IgG $ is the main antibody in the secondary response. It crosses the placenta. $ IgA $ is the predominant antibody class in seromucous secretions such as saliva, tears, colostrums and respiratory, gastrointestinal and urinogenital secretions. $ IgA $ provides the first line of defence against invading pathogens, inhibiting their adherence to the mucosal cells and to preventing their invasions of the body.