Question

A child is suffering from recurrent chronic infections with encapsulated bacteria is due to deficiency of subclass:

• A. IgG1
• B. IgG2
• C. IgG3
• D. IgG4

Answer 1

The Correct Option is B

Recurrent infections with encapsulated bacteria in children are often due to specific immunodeficiency. The immunoglobulin G (IgG) subclass that plays a crucial role in dealing with encapsulated bacteria is IgG2. This subclass is responsible for mounting an immune response against polysaccharide antigens, which are present on the surfaces of encapsulated bacteria.

Here's a breakdown of the immunoglobulin IgG subclasses and their functions to understand why IgG2 is the correct answer:

IgG Subclass	Function
IgG1	It is the most common IgG subclass and is effective against protein antigens.
IgG2	Specializes in responding to polysaccharide antigens, typical of encapsulated bacteria like Streptococcus pneumoniae and Haemophilus influenzae.
IgG3	Strongly mediates antibody-dependent cellular cytotoxicity and complements activation.
IgG4	Involved in responses to allergens and chronic antigen exposure.

Children with IgG2 deficiency have difficulty with encapsulated bacteria because of impaired opsonization and clearance of these pathogens. Therefore, recurrent infections are likely due to the inability of the immune system to effectively target the polysaccharide antigens presented by encapsulated bacteria.

In summary, the deficiency in IgG2 leads to the inability to respond adequately to polysaccharide antigens, causing susceptibility to infections with encapsulated bacteria.