How many antigen-binding sites does a typical IgM molecule have?

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Multiple Choice

How many antigen-binding sites does a typical IgM molecule have?

Explanation:
IgM is a pentamer, made up of five identical IgM units. Each IgM unit has two antigen-binding sites (Fab regions). So, with five units, the total number of antigen-binding sites is 5 × 2 = 10. This arrangement gives IgM high overall binding strength (avidity) right at the start of an immune response, helping to trap pathogens and efficiently activate complement. In its secreted form, the pentamer is stabilized by a J chain, but the number of binding sites remains ten.

IgM is a pentamer, made up of five identical IgM units. Each IgM unit has two antigen-binding sites (Fab regions). So, with five units, the total number of antigen-binding sites is 5 × 2 = 10. This arrangement gives IgM high overall binding strength (avidity) right at the start of an immune response, helping to trap pathogens and efficiently activate complement. In its secreted form, the pentamer is stabilized by a J chain, but the number of binding sites remains ten.

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