What are the types of human immune cells?

Under normal circumstances, human immune cells include lymphocytes, natural killer cells, monocytes and macrophages, neutrophils, and mast cells. A detailed analysis is as follows:

1. Lymphocytes: These include T lymphocytes and B lymphocytes. T lymphocytes mature in the thymus and exert immune functions by secreting cytokines and directly killing target cells. B lymphocytes originate from pluripotent stem cells in the bone marrow and can generate antibodies and present antigens, thereby eliminating pathogens through antibody-antigen binding.

2. Natural Killer Cells: These cells can directly kill target cells, including tumor cells and virus-infected cells, without prior exposure to antigens. They play a significant role in anti-viral and anti-tumor responses.

3. Monocytes and Macrophages: Monocytes originate from hematopoietic stem cells in the bone marrow and circulate in the blood; upon entering tissues, they differentiate into macrophages. Macrophages can engulf and digest pathogens and cellular debris, while also secreting cytokines to regulate immune responses.

4. Neutrophils: Derived from hematopoietic stem cells in the bone marrow, neutrophils exhibit chemotaxis and selective phagocytic capabilities, forming an important barrier against bacterial invasion and effectively killing pathogenic bacteria that enter the body.

5. Mast Cells: Found in mucosal tissues such as the skin and respiratory tract, mast cells participate in allergic and inflammatory reactions. They can release substances such as histamine and leukotrienes, triggering responses such as vasodilation and edema.

In summary, there are numerous types of human immune cells, each with unique functions and characteristics, collectively forming the human immune system that protects the body from pathogens and diseases.