Neutralization involves the binding of certain antibodies (IgG, IgM, or IgA) to epitopes on the surface of pathogens or toxins, preventing their attachment to cells.

Neutralization

Agglutination or aggregation occurs when pathogens are cross linked by antibodies to create large aggregates. When large aggregates develop phagocytes can ingest them easier. The pentameric structure of IgM provides ten Fab binding sites per molecule, making it the most efficient antibody for agglutination.

Agglutination

The coating of a pathogen with opsonin, tagging it for phagocytic cells to easily recognize and destroy it

Opsonization

Can be more efficient when activated by specific antibody produced by the adaptive immune response. The specific antibody attaches to the pathogen to form an antibody-antigen complex, activating mutlipart protein C1. C1 then recruits other complement proteins in a cascading manner.

Complement Activation: Classical Pathway

Antibodies have many functions to help facilitate an adaptive immune response:
- Antibody-dependent cell-mediated cytotoxicity (ADCC)
- Opsonization
- Neutralization 
- Agglutination
- Activation of The Complement System

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B Cells are responsible for the production of antibodies, also called immunoglobulins. Antibodies are present in both the blood and tissue fluids and are involved in the body’s defense against pathogens and toxins.

Antibodies

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The constant region of an antibody molecule determines its class, or isotype. The five classes of antibodies are:
- IgG
- IgM
- IgA
- IgD
- IgE

Classes of Antibodies 

Functions of Antibodies

The constant region of the antibody molecule includes the trunk of the Y and lower portion of each arm of the Y. The trunk of the Y is also called the **Fc region**, for “fragment of crystallization,” and is the site of complement factor binding and binding to phagocytic cells during antibody-mediated opsonization.

Fc Region of Antibodies

The two 'arms' of the Y-shaped antibody molecule are known as the **Fab region**, for "fragment of antigen binding." The far end of the Fab region is the variable region, which serves as the site of antigen binding.

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