Question

Which class of antibody opsonizes antigents for phago- cytosis through two different pathways?

• A. Immunoglobulin G (IgG)
• B. Immunoglobulin M (IgM)
• C. Immunoglobulin A(IgA)
• D. Immunoglobulin E (IgE)

Answer 1

The Correct Option is A

The question asks which class of antibody is responsible for opsonizing antigens, which means marking them for phagocytosis, through two different pathways. Let's analyze the options: 

1. Immunoglobulin G (IgG)
   • Direct phagocytosis enhancement: IgG binds directly to antigens on the pathogen. Phagocytes have receptors that recognize the Fc region of IgG, which facilitates direct uptake and destruction of the pathogen.
   • Complement activation: IgG can activate the classical complement pathway, which further leads to the opsonization of antigens. Products of the complement system, like C3b, coat the pathogen and promote its uptake by phagocytes.
2. Immunoglobulin M (IgM)
3. Immunoglobulin A (IgA)
4. Immunoglobulin E (IgE)

Therefore, the correct answer is Immunoglobulin G (IgG), as it is uniquely capable of opsonizing antigens for phagocytosis via both direct engagement of phagocyte receptors and complement activation.