How do antibodies in blood fight infections?

Antibodies in blood fight infections by identifying, binding to, and neutralising harmful pathogens such as bacteria and viruses.

Antibodies, also known as immunoglobulins, are proteins produced by the immune system in response to an infection. They play a crucial role in the body's immune response by recognising and binding to specific antigens, which are foreign substances such as bacteria, viruses, and other harmful pathogens. This process is known as antigen-antibody interaction.

The structure of an antibody is Y-shaped, with two identical antigen-binding sites at the tips of the 'Y'. These sites are highly specific and can only bind to a particular antigen. This specificity is due to the unique shape and chemical properties of the antigen-binding sites, which match perfectly with the antigen's structure. This is often compared to a lock and key mechanism, where the antibody (the lock) can only be 'opened' by the correct antigen (the key).

Once an antibody has bound to an antigen, it neutralises the pathogen in several ways. It can block the pathogen's ability to invade cells, thus preventing the pathogen from causing further harm. Antibodies can also 'tag' pathogens for destruction by other immune cells, a process known as opsonisation. In addition, they can trigger a process called complement activation, which leads to the formation of a membrane attack complex that can puncture the pathogen's cell wall, causing it to burst and die.

Furthermore, antibodies play a role in immune memory. After an infection, some of the antibodies remain in the body, providing long-term protection against the same pathogen. If the same pathogen enters the body again, these memory antibodies can quickly recognise and neutralise it, often before it causes any symptoms. This is the principle behind vaccination, where a harmless form of the pathogen is introduced to stimulate the production of memory antibodies.

In summary, antibodies are a vital part of the immune system, providing a specific and effective defence against infections. They identify, bind to, and neutralise harmful pathogens, and also contribute to immune memory, offering long-term protection against diseases.