This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology Pa 1 (Immune Response, Antigen-Antibody Reactions, Hypersensitivity, Structure of Immune System, Immunodeficiency Disorders), Subject name: Microbiology
[{'content': 'The earliest immunoglobulin to be synthesized by the fetus is - \nSelect and explain. \nA. IgA, B. IgG, C. IgE, D. IgM', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Option 1, 3, 4 IgM: IgM is the first immunoglobulin to be synthesized by a neonate in about 20 weeks of age. IgM is not transpoed across the placenta; hence, the presence of IgM in the fetus or newborn indicates intrauterine infection. The first immunoglobulin produced in response to an antigen is IgM. after 3 monts of bih class switching is staed and then other class of immunoglobulins are synthesised. IgM is secreted as a pentamer and is composed of five H2L2 units (similar to one IgG unit) and one moleculeof a J chain.. It is the most efficient Because its interaction with antigen can involve all 10 binding sites, it has the highest binding capacity and cross-linking of all the immunoglobulins. Option 2 IgG is the only immunoglobulin class to cross the placenta and therefore is the most abundant immunoglobulinin newborns.( this is not the the first to be synthesised in newborn)', 'role': 'assistant'}]