The attachment of antibodies to antigen molecules on the outside of a pathogen can have various effects. It may, depending on which antigens are affected, stop the functioning of the pathogen entirely. White blood cells called phagocytes can crawl around the body and literally eat up material that is signalled as ripe for destruction. A coating of antibodies around a pathogen can be one way of encouraging phagocytosis. Another part of the immune system is responsible for dealing with the rather different set of problems posed by viruses.
Viruses are much smaller than bacteria and multiply inside our own cells.
To eliminate them, the body needs to identify and kill virus-infected cells before they release a deadly cargo of new viruses. A type of white cell known as the T cell is able to do this. Fortunately for the immune system, most viruses cause the cells they are infecting to carry virus antigens on their surface. A layer of cells is killed, and so your throat feels sore. In many infectious diseases, most of the damage is actually done by our own immune systems.