Which statement is incorrect regarding naturally occurring antibodies?

Which statement is incorrect regarding naturally occurring antibodies?

• A. They are usually IgM
• B. react best in saline
• C. react best at 4C
• D. They cross the placenta

Answer: (D)

Naturally occurring antibodies are the antibodies you already have without prior exposure, with ABO antibodies being the classic example. They are usually IgM, a pentamer, which makes them very effective at binding carbohydrate antigens on red cells. Because they are IgM and act best in cold or saline conditions, they commonly react at 4°C or in saline at room temperature, giving a strong immediate-spin reaction. The ability to cross the placenta is a property of IgG antibodies, not IgM, so these natural antibodies do not cross the placenta. That’s why the statement about crossing the placenta is incorrect.

Naturally occurring antibodies are the antibodies you already have without prior exposure, with ABO antibodies being the classic example. They are usually IgM, a pentamer, which makes them very effective at binding carbohydrate antigens on red cells. Because they are IgM and act best in cold or saline conditions, they commonly react at 4°C or in saline at room temperature, giving a strong immediate-spin reaction. The ability to cross the placenta is a property of IgG antibodies, not IgM, so these natural antibodies do not cross the placenta. That’s why the statement about crossing the placenta is incorrect.