Defence against pathogens

There are numerous pathogens in our environment, such as viruses, bacteria, and fungal and animal parasites (e.g. malaria parasites). Our body needs a system to defend it against these dangerous invaders. The white blood cells are involved in this defence system. A distinction is drawn between two types of defences in this context:

The first-line, quick-response defence

• The invading pathogens trigger an alarm in the body.
• White blood cells, primarily granulocytes, make their way to the pathogens (e.g. in a wound). The affected part of the body becomes flushed and warm; it swells and hurts – inflammation sets in.
• The body raises its temperature – the person develops a fever.
• The granulocytes attempt to surround and consume the invading pathogens. The granulocytes themselves die in this process.
• Later, the cells known as the “big eaters” of the immune system (monocytes, macrophages) arrive and help with this task. Pus is formed through the accumulation of phagocytes.

1. The monocyte approaches the invader.
2. It begins to wrap itself around the invader.
3. The ends of the monocyte merge together: the invader is ingested by the monocyte.
4. The monocyte breaks down and digests the invader.

Slower-response, tailored defence

Lymphocytes play the main role in this type of immune response:

• Lymphocytes identify the pathogens invading the body (bacteria, viruses) and begin to produce large numbers of antibodies that are precisely tailored to fighting those specific pathogens. Antibodies that are specifically tailored to each type of virus or bacteria are created. This process can take a few days.
• Once the antibodies are ready, they combine with the invaders. This combination is the first step towards the pathogens’ destruction.
• At this point, the macrophages get to work, engulfing and breaking down the pathogens.
• If the pathogens are defeated, some of the lymphocytes retain the recipe for building these specific antibodies in their “memory”. If the same pathogens attack the body again later, even years later, the right antibodies can be produced very quickly, enabling the destruction of invading pathogens before they can reproduce themselves in great numbers. The body is now immune to this illness; thus, the individual will not succumb to it again or will experience only mild symptoms.