Which of the following immunoglobulins is found in highest concentration in human blood serum and is capable of crossing the placenta to provide passive immunity to the developing fetus?

💡 Solution & Explanation

Immunoglobulin G constitutes approximately seventy-five percent of serum antibodies in humans and is the only antibody isotype capable of crossing the human placenta to confer passive immunity to the fetus. Immunoglobulin A is predominant in mucosal secretions like saliva and breast milk, while Immunoglobulin M is the first antibody produced during primary immune responses. Immunoglobulin E mediates immediate hypersensitivity reactions and allergic responses against parasites. Humoral immunity relies heavily on antibody production by plasma cells.