1. Phagocytes: These cells are the first line of defense, engulfing and destroying pathogens (like bacteria, viruses, and fungi) through a process called phagocytosis. There are two main types:
* Neutrophils: The most abundant type, they are the first to arrive at the site of infection. They are highly effective at killing bacteria.
* Macrophages: These cells are larger and live longer than neutrophils. They also act as "scavengers," clearing debris and dead cells from the body. They play a critical role in initiating and coordinating the immune response.
2. Lymphocytes: These cells are responsible for specific immune responses, recognizing and targeting specific pathogens. There are two main types:
* T lymphocytes (T cells): They are responsible for cell-mediated immunity. They directly attack infected cells or kill pathogens. Different types of T cells include:
* Cytotoxic T cells: Kill infected cells.
* Helper T cells: Help activate other immune cells like B cells and cytotoxic T cells.
* Regulatory T cells: Suppress immune responses to prevent autoimmune reactions.
* B lymphocytes (B cells): They are responsible for humoral immunity. They produce antibodies, which bind to specific pathogens and mark them for destruction by other immune cells.
3. Natural Killer (NK) cells: These cells are part of the innate immune system and kill infected cells and cancer cells without the need for prior sensitization. They are a crucial defense against early infection and tumor formation.
4. Other Immune Cells:
* Mast cells: Release histamine and other chemicals that cause inflammation.
* Eosinophils: Fight parasitic infections and allergic reactions.
* Basophils: Release histamine and other chemicals involved in allergic reactions.
These immune cells work together in a complex and coordinated fashion to protect the body from infection and disease. They constantly circulate throughout the body, searching for and destroying pathogens.
