The immune system is the body’s natural defense system that critically identifies foreign invaders – the self from the non-self – and protects the body against cellular damage, infections and disease.
It comprises of a complex network of organs, cells, proteins and chemicals that work together to defend against invaders such as bacteria, viruses, fungi, parasites and other pathogens.*
A primary component of the immune system is white blood cells or leukocytes, that circulate in the body looking for invaders. They are stored in the lymphoid organs – the bone marrow, thymus, spleen and lymph nodes. The immune system also includes other organs: the tonsils and adenoids (in the throat and nasal passage, respectively), the stomach and bowel and the skin and mucous membranes.
Types of immunity
We have three types of immunity: innate, adaptive or passive.
1. Innate immunity: Your first line of defense
The innate immune system is inherited and active from the time you’re born. It’s your body’s first line of defense and its function is to recognise and stop the spread of the pathogen. It consists of all the outer and inner surfaces of the body, i.e. the skin and mucous membranes, as well as the defense cells, proteins and chemical substances like stomach acid or mucus. When bacteria enters the body through a small wound, for instance, the cells of your innate immune system engulfs the bacteria and destroys it, usually within a matter of hours. The response is immediate and non-specific.
2. Adaptive immunity: Your second line of defense
Adaptive or acquired immunity is the immunity you get from exposure to antigens*. When the invader evades the innate immune system, the adaptive immune system provides a pathogen- and antigen-specific response.
The adaptive immune system detects, identifies and destroys the invader, usually within a few days. The cells then develop an immunological memory, where each pathogen is “remembered” by its antigen. So the next time it encounters the same bacteria, for instance, it “recognises” the bacteria and reacts faster. This is how your body develops immunity to a pathogen and why we only get some illnesses once in our lifetime.
The more pathogens we’re exposed to, or when we get vaccinated, the more our body builds up a store of antibodies.
3. Passive immunity
Passive immunity is immunity that we get from antibodies produced from other than our own body, for instance, the immunity that a baby receives from its mother in-utero or through breastmilk.
*Pathogens are microorganisms that can cause disease.
*An antigen is any substance that sparks the immune system in producing antibodies against it.