This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
A 3 year old child presents with a history of repeated sinopulmonary infections caused by encapsulated organisms. Which of the following is most likely to be deficient in this case? 
Select and explain. 
A. IgG4, B. IgG3, C. IgG2, D. IgG1
C: IgG2
Answer: C: IgG2 
Explanation: Deficiency of IgG2 results in recurrent sinopulmonary infections with encapsulated organisms. Deficiency of IgG1 - Bacterial infections (Diptheria, tetanus) Deficiency of IgG3 - Viral infections Deficiency of IgG4 - Parasitic infections IgG is the only maternal immunoglobulin that is normally transpoed across the placenta and provides natural passive immunity to the newborn. Maximum placental transfer - IgG1 Minimum placental transfer - IgG2 Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition