Diseases: The Human Immune System

The human immune system is the body’s defense against infectious microorganisms such as bacteria, viruses, and fungi.
The system comprises two components: the innate system, a general defense system, and the adaptive immune system, a specialized system targeting specific pathogens.
The innate system includes physical barriers such as skin, chemical barriers like stomach acid, and immune cells such as neutrophils and macrophages.
When a pathogen enters the body, it is first encountered by the innate system. Macrophages and neutrophils work to engulf and digest the invaders.
Besides physical actions, they also produce chemicals causing inflammation and fever, making the environment less suitable for the pathogen to survive.
If the innate system is unable to fully eliminate the pathogen, the adaptive system kicks in. It involves T cells and B cells, two types of lymphocytes.
T cells recognize abnormalities by binding to infected cells and eliminate them. There are two types of T cells: Helper T cells, which ‘help’ other immune cells respond to the pathogens and Killer T cells, which directly kill infected cells.
B cells produce antibodies. Each B cell is programmed to make one type of antibody. When the B cell meets its trigger, it duplicates rapidly, creating many cells producing the same antibody.
Antibodies have two main functions: to neutralize the pathogen by binding to it and making it easier for other cells to engulf it, and to cause infected cells to be destroyed by other immune cells.
After an infection is fought off, some T and B cells become memory cells. These cells remember the specific pathogen and mount a faster response if the body is infected by the same pathogen again, hence leading to immunity.
Vaccinations work precisely by activating this response, making the body ‘remember’ a safe version of a pathogen so it can respond rapidly when encountering the real one.
Autoimmune diseases occur when the immune system wrongly identifies healthy body cells as foreign and attacks them. Examples include multiple sclerosis and type 1 diabetes.
The human immune system can also be compromised, making individuals more susceptible to infections. This can be due to genetic factors or conditions like HIV/AIDS, which damages the immune system.

This information covers the key areas related to the Human Immune System for the Interactions with the Environment revision content. Understanding these key concepts should provide a solid foundation for answering related questions.