Great question, Francis! There are two basic parts of the human immune system: the innate system, and the acquired system.

The innate immune system is what all humans are born with, and provides a basic level of protection against diseases and other potentially harmful things. The acquired immune system is what creates antibodies against new diseases, and that changes throughout your life; vaccinations can lead to your acquired immune system being able to fight off more new diseases.

The components of these systems can be found throughout the body’s organs. For example, skin, bone marrow, lymph nodes all produce various players in the immune system to fight infections in the body. The innate system and acquired system work together to mount a defense against pathogens in human bodies.

Sources: Chaplin 2006 , National Institute of Allergy and Infectious Diseases , Johns Hopkins Medicine.

The immune system is made up of many parts. On the organ and tissue level, this includes the bone marrow, thymus, lymph nodes, blood vessels, lymphatic vessels, spleen, and skin.

Briefly, the function of each is summarized below:
- bone marrow: Immune cells originate here (cells begin as stem cells and differentiate to red blood cells, white blood cells, platelets, etc.)
- thymus: Where certain white blood cells ("T cell") mature.
- lymph nodes: Tissue full of immune cells. These are located throughout the body, and the ones you might most normally notice are the ones on the sides of your neck.
- blood vessels: Carries "lymph" fluid full of immune cells throughout the body, collecting debris/cellular damage in the bloodstream and eventually bringing this fluid to certain lymph nodes for filtering.
- lymphatic vessels: Carry filtered lymph fluid towards the heart.
- spleen: An organ that produces immune cells and has blood continuously moving through, as the spleen detects pathogens (virus, bacteria) to produce more immune cells.
- skin: An important physical barrier for all of the things you can imagine! We encounter many germs daily, and even our skin is a good first level of protection.