Immune response

An immune response is how our bodies protect themselves from harmful things like toxins, viruses, bacteria, protozoa, helminths, and fungi. These can make us very sick if our bodies don’t fight them back. Our immune system has special tools and cells that work together to find and remove these invaders.

There are two main parts to the immune response: the innate system and the adaptive system. The innate system is our first line of defense. It includes things like our skin and mucus, as well as special cells like neutrophils, macrophages, and monocytes. This system reacts quickly but not very specifically to any invader.

The adaptive system is slower to start but is very specific. It remembers past invaders and can respond even faster if the same invader tries to attack again. This is why vaccines are helpful. They introduce a weakened part of a germ to start the immune response without causing sickness. Then, if the real germ tries to infect us later, our body can fight it off quickly thanks to memory T and memory B cells made during the first exposure. This helps keep us healthy and safe from many diseases.

Innate part

Further information: Innate immune system

The innate immune response is the body's first way to fight off harmful things like germs. It works for many different kinds of living things and includes barriers like your skin and the lining in your nose and throat, called mucous membranes. It also uses special cells such as neutrophils, macrophages, and monocytes, along with important chemicals known as cytokines and something called complement.

When harmful germs get past these barriers, special parts on immune cells called pattern recognition receptors (PRR) can find and grab pieces of the germs. This starts a chain of events inside the cells that tells them to release more cytokines. These cytokines help bring more defense cells, like neutrophils, from the blood vessels to the area where the germs are. These cells can then surround and destroy the germs.

The complement system has three different ways to work, each starting in a different way but all helping to fight infections by marking germs for destruction and causing inflammation, which is a natural response that helps the body fight back against infection.

Adaptive part

Further information: Adaptive immune response

The adaptive immune response is the body's second line of defense. It uses special cells called B and T cells that can find specific harmful substances, called antigens. These cells learn to recognize what to fight.

When certain cells called antigen-presenting cells (APCs) show a foreign antigen, they help activate T cells. These APCs include dendritic cells, B cells, and macrophages. Once helper T cells are activated, they help B cells in the lymph node. B cells then make antibodies to fight the invaders.

The adaptive immune response is slower than the body's first defense because it needs these specific cells to be ready. But it can remember past invaders. If the same antigen appears again, the immune system can respond faster and stronger thanks to memory T and B cells.

Types of immune response

Our bodies have special ways to fight off germs and stay healthy. These are called immune responses. There are different types depending on what we’re fighting.

One type fights off viruses and tiny parasites inside cells. Another type helps protect us from harmful substances and bigger parasites. A third type deals with bacteria and fungi outside cells. Each type uses different cells and tools to keep us safe.