Question: Different cytokines induce the isotype change of the different classes of antibodies. Of the following cytokine / isotype pairs, choose the correct one: 
 Options:  <1> IL-4 / IgE. <2> IL-4 / IgM. <3> IL-5 / IgG. <4> IFN- / IgM. <5> TGF- / IgA.
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