<prompt> Immunoglobulin involved in Type I hypersensitivity reaction: March 2013 bIgAIgMIgEIgG  <response>: Ans. C i.e. IgE Immunoglobulins First antibody to be synthesized after primary immunization: IgM First antibody to be synthesized after exposure to new antigen: IgM First antibody to be synthesized by fetus: IgM Antibody which fixes complement: IgM Only immunoglobulin that crosses placenta: IgG Immunoglobulin found in mucous secretions saliva, tears, colostrum etc.: IgAsecretory antibody Immunoglobulin elevated in atopic diseases asthma, hay fever etc.: IgE Immunoglobulin mediating reaginic hypersensitivity: IgE 