Discuss the mechanisms by which antibodies contribute to the immune response and prevention of illness.

Answer

Antibodies are produced by the B cells, and they prevent illnesses and fight pathogens through three main ways
(a) preventing the antigen from binding to its target,
(b) tagging a pathogen for destruction by macrophages or neutrophils
(c) activating the complement cascade.

Explanation

The antibodies resemble the receptors on human cells which the pathogen use in order to infect humans and enter the cells. Since they have the same structure as those ligands on cells, an antibody will bind the pathogen thus neutralizing them and they are thus unable to bind further to the cells, making it easier for their destruction by macrophages
The antibodies also tag the pathogen and may present them to macrophages or even by the use of MHCI or MHCII which all aid in removal of the pathogen from the system
Antibodies also activate complement cascade like the classical and alternative complement pathways which causes lysis of infectious organisms, activation of inflammation, opsonization and immune clearance.
References
https://www.ncbi.nlm.nih.gov/books/NBK27100/