Which statement about antibodies is correct?

IgG - Crosses the placenta

Among the options provided, the correct statement regarding antibodies is:

(b) IgG - Cross placenta

IgG antibodies are the most abundant type of immunoglobulins in the bloodstream. They play a crucial role in providing long-term immunity against various pathogens. IgG antibodies are capable of crossing the placental barrier, which allows them to be transferred from a pregnant woman to her developing fetus. This transfer of IgG antibodies provides passive immunity to the newborn, helping protect them from infections during the early stages of life.

Option (a) IgA - Helps in allergic reaction is incorrect. IgA antibodies are primarily associated with mucosal immunity and provide defense against pathogens in body secretions such as saliva, tears, and breast milk. They are not directly involved in allergic reactions, which are primarily mediated by IgE antibodies.

Option (c) IgE - Found in secretions is incorrect. IgE antibodies are primarily involved in allergic reactions and immune responses against parasitic infections. They are not typically found in secretions such as saliva or breast milk but rather in blood and tissues.

Option (d) IgM - Exist as dimer is incorrect. IgM antibodies are the first antibodies produced during the primary immune response to an infection. They exist as a pentamer (consisting of five antibody subunits) rather than a dimer.

Therefore, the correct option is (b) IgG - Cross placenta, as IgG antibodies can cross the placenta and provide passive immunity to the fetus.