Thread by @Dave_it_up

Thank you, Emmanuel, for your excellent post! Here is a definition list of the immune cells you talked about, along with their functions. Understanding these immune cells is crucial because they form the basis of how our body defends itself against infections and diseases.

1. Lymphocytes
These are a type of white blood cell that plays a key role in the immune system, and they come in three main forms:

- T Cells: These cells are critical for identifying and attacking infected cells in the body. There are different types of T cells:
- Helper T Cells: Help other immune cells by releasing chemicals (cytokines, which are signaling molecules that help coordinate the immune response) that boost the immune response.
- Cytotoxic T Cells: Directly kill infected cells or cancerous cells.
- Regulatory T Cells: Help to control or "regulate" the immune response, preventing overactivity that could lead to autoimmune diseases.

- B Cells: These cells are responsible for producing antibodies. Antibodies are proteins that bind to foreign invaders like viruses or bacteria, marking them for destruction.

- NK (Natural Killer) Cells: These are part of the innate immune system, meaning they don’t need to recognize a specific invader. The innate immune system provides a general defense against infections, unlike the adaptive immune system, which targets specific pathogens after prior exposure. They are particularly good at detecting and destroying cells that are infected or have become cancerous.

2. Neutrophils
These are the most abundant type of white blood cell and are among the first responders to infection. They primarily attack bacteria and fungi, engulfing and digesting them through a process called phagocytosis (the process by which cells engulf and break down pathogens or particles). They act fast, but they also have a short life span, often dying in the process of defending the body.

3. Macrophages
These are large white blood cells that play a vital role in both the innate and adaptive immune responses. They engulf pathogens (like bacteria, such as Salmonella, or viruses, like influenza) and debris through phagocytosis. Once they’ve digested the invader, macrophages can also present pieces of the invader (antigens) on their surface to other immune cells, helping to stimulate a more specific immune response. Because of their large size, even though they make up a smaller percentage of immune cells by number, they contribute significantly to the overall mass of immune cells.

4. Bone Marrow and Thymus
These are two critical organs for immune cell production. The bone marrow produces most of the immune cells, including all types of lymphocytes, and is the birthplace for neutrophils and macrophages as well. The thymus is a small organ located in the chest, where T cells mature and learn to differentiate between the body’s own cells and foreign invaders.

5. Lymph Nodes and Spleen
These organs serve as hubs where immune cells are stored, activated, and sent out to battle infections. The lymph nodes act like filters, trapping invaders like bacteria or viruses, and giving immune cells the chance to mount an attack. The spleen helps filter blood and also plays a role in housing immune cells, particularly lymphocytes.

6. Changes with Age and Disease
As people age, the bone marrow and thymus produce fewer immune cells, leading to a generally weaker immune system, which increases susceptibility to infections and other diseases. Obesity and infections can also change the distribution and number of immune cells, often causing imbalances that can either weaken the immune response or cause it to become overactive, leading to inflammation and tissue damage.

This detailed understanding of the different immune cells and their roles gives a more complete picture of how our body fights off infections and diseases, including the response to viruses like SARS-CoV-2.