What is the mechanism of antibody action?

There are 3 different mechanisms that antibodies use to inhibit infection.

1. One mechanism is by preventing the antigen from binding to its target. Antigens can be thought of as acting as molecular keys and the target molecules being the locks. Antibodies function as barriers that block the antigens from fitting into the target molecules; by impeding this binding process, antibodies effectively neutralize the harmful effects that antigens may induce. 
2. Another mechanism of antibody action involves tagging a pathogen for elimination by neutrophils or macrophages. When the immune system identifies a harmful pathogen, it creates antibodies that stick to the pathogen's surface, essentially labeling it as a threat to the body. Macrophages and neutrophils recognize these antibodies and proceed to engulf and destroy the tagged pathogens. 
3. Another mechanism of antibody action involves initiating the complement cascade. When the immune system perceives a threat, it initiates a cascade of events. Each sequential step in this cascade serves to activate the subsequent one, resulting in a series of reactions that ultimately lead to the neutralization of the invading pathogen. These responses may involve the disruption of the pathogen's structure or the recruitment of additional immune cells.