Immune response to viral infections
The immune response to viral infections is a complex defense mechanism that enables the human body to combat viral threats effectively. When viruses invade host cells, they replicate and integrate their genetic material, prompting the immune system to launch a counterattack. This response includes both humoral and cellular components. The humoral immune response generates specific antibodies that neutralize viral particles, while the cellular immune response involves T-cell lymphocytes that target and destroy infected cells.
Key players in this defense include interferons, which inhibit viral replication and enhance the activity of other immune cells, and cytotoxic T-cells, which directly kill infected cells to prevent further viral spread. Natural killer cells also play a significant role by binding to antibodies attached to viruses and promoting cell death through cytokine release. Overall, the immune response is crucial for survival against viral infections and showcases the body's ability to adapt and protect itself from diverse pathogens.
Immune response to viral infections
Definition
Viral infections are caused by viral particles that replicate in the host cell. These viral particles then produce more genetic material for new particles and also incorporate their own genetic material into the host cell’s genome. As part of its immune response, the human immune system attacks these viral particles to undermine their effect on the body.
Viruses are fought with specific and nonspecific mechanisms, involving either a humoral or cellular response. These two immune responses involve the formation of specific antibodies that are generated to kill viral antigens, the production of interferon by host cells to inhibit viral function, and the production of natural killer cells that recognize and kill the virus.
Specific Types
Humoral immune response. A humoral (body fluid) response to viral infection blocks or neutralizes the viral particles’ ability to infect a host cell. The immunoglobulin genes in the human immune system are integrally involved in this process. When viruses infect a human host cell, they are considered foreign antigens. The human host cell will then generate antibodies that recognize the specific antigen. Once an antibody is formed, it will then continue to replicate and attack the antigen, thereby neutralizing the viral impact on the host cell.
Cellular immune response. A cellular response to viral infection kills the virus by attacking proteins that reside on viral cell surfaces, such as glycoproteins, or by attacking core proteins of the virus. This attack is made by T cell lymphocytes that will recognize the cell surface proteins of a virus. The killer T cells will destroy the cell and the virus in the cell. Another cellular response is the production of interferons, which are hormones produced by the body when viruses are present.
Specific Methods
Interferons. Interferons (IFNs) are proteins made by lymphocytes produced in the human immune system that are released in response to a viral infection. IFNs are part of a group of cytokines that “interfere” with viral replication within the host human cell. They also activate other immune cells, such as natural killer cells and macrophages, and increase the recognition of viral infections for other immune cells to respond. Before a human cell is killed by a virus, it first produces and releases IFNs. These IFNs will then communicate with neighboring host cells to set off a chain reaction to produce and release protein factors called interferon-stimulated genes, which will fight the virus.
Cytotoxic T-cell lymphocytes. Cytotoxic T-cell lymphocytes (CTLs) are virus-specific cells that recognize specific viral antigens that have been synthesized or produced within a human cell. These cells are located on the cell surface on virtually all somatic cells in the human body, so they can respond to practically all the viral antigens it recognizes. CTLs can destroy these viral particles. However, CTLs, in the process of destroying viral particles, also can destroy the involved human cell, which could lead to more damage and injury to the human body. Liver damage, for example, is caused by the virus-specific CTL rather than by the virus itself in the case of hepatitis B infection.
Natural killer cells. Antibody-dependent cell-mediated cytotoxicity (ADCC) is a mechanism in the human immune system and part of cell-mediated immunity that involves effector cells to lyse, or kill, a pathogen (such as a virus) that has been bound by antibodies. Thus, as part of the humoral immune response, antibodies are released to bind to a viral particle, thereby allowing other cells in the immune system to attach to the antibody-antigen complex and destroy it directly.
One ADCC method is the activation of natural killer (NK) cells, which will recognize part of the antibody that is attached to the virus. NK cells are large granular lymphocytes produced by the immune system that make up approximately 2 to 5 percent of peripheral blood lymphocytes. These NK cells, once attached to the viral-antibody complex, will release cytokines, such as interferons and cytotoxic granules, that enter the target cell and promote cell death by triggering the apoptosis (regulated cell death) process. This process is similar, but independent of, responses by CTLs.
Impact
All living organisms, including humans, must develop protective mechanisms against infectious organisms, including viruses, to survive. The complexity of the many infectious particles found on Earth has forced the human body to develop numerous and complicated methods to fight these foreign substances. These methods, which include producing and releasing vast amounts of specific and nonspecific proteins to fight infection, define the immune response.
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