Which immunoglobulin class is found in highest concentrations in human blood serum and can cross the placental barrier to protect the fetus?

💡 Solution & Explanation

Immunoglobulin G constitutes the highest proportion of antibodies circulating in human blood serum and possesses the unique structural capability to cross the placenta, conferring passive immunity to the developing fetus. Other classes like IgA are predominantly found in mucosal secretions and breast milk, whereas IgE mediates immediate hypersensitivity and allergic reactions. IgG represents the principal antibody of secondary immune responses against bacterial and viral infections.