Tek 4C Researchable

By: Courtney Roberts

Q: HOW DOES YOUR BODY FIGHT OFF VIRUSES?

Immune Response

In humans and other animals, the skin acts as the first defense against viral infection. Skin serves as a barrier to viruses and other germs. If a virus penetrates this barrier, the bodys innate immune system is mobilized. This system, which is always active, recognizes the presence of a virus by sensing the viral nucleic acid or proteins. The cells of the innate immune system then produce a variety of proteins, called the cytokines, to stop the viral infection. One group of cytokines, called interferons, help make proteins that disrupt different stages of the viral reproduction cycle.

Adaptive Immune Response

If viruses reproduce faster than the innate immune response can destroy them the adaptive immune system is activated. There are two forms of the adaptive immune response, the humoral immune response and the cell mediated immune response. In the humoral immune response the cells called B lymphocytes produce large proteins called antibodies. The antibodies attach to virus particles and hinder their ability to infect cells. T lymphocytes, which are part of the cell mediated immune response, can kill virus-infected cells.

Vaccines

Vaccines prevent many viral infections. They provide immunity against certain viruses by activating the body's adaptive immune response. Immunizing a number of individuals can halt the spread of a virus through a population. There are three main types of vaccines, inactivated vaccines, attenuated virus vaccines, and subunit vaccines. An inactivated vaccine is produced by growing large amounts of virus and chemicals are used to disable the virus's ability to infect cells. The inactive virus stimulates the body's immune system, producing immunity against the virus. Attenuated virus vaccines consist of infectious viruses in a weakened form. The viruses replicate in the host but do not cause disease and immunity is acheived. Subunit vaccines include proteins identical to those that make the protective coat of a particular virus. These proteins can self assemble into virus like particles, but they lack viral nucleic acid. They cannot infect cell or cause disease, but when injected as a vaccine they activate the immune response helping immunity develop.

Antiviral Drugs

Antiviral drugs may be used to block virus infections when no vaccines are available or in people who have not been immunized. They usually do not cure viral diseases but they can shorten the duration of the disease and lessen severity of the symptoms. Such drugs, however, are difficult to develop based on the fact that viruses depend upon host cells for much of their replication. Therefore it is hard to identify drugs that block the virus without harming the host cell.