A summary of the major cells of the innate immune system and their functions

Major Innate Immune Cells

• Macrophages
• Neutrophils
• Monocytes
• Mast cells
• Eosinophils
• Basophils
• NK cells
• Dendritic cells

Phagocytes

Phagocytes are cells that engulf and digest foreign particles, microbes, and debris.

Primary Phagocytes

• Macrophages
• Neutrophils

Macrophages

• Large, irregularly shaped phagocytes.
• Develop from circulating monocytes.
• Migrate from blood into tissues.
• Release cytokines to recruit other immune cells.

Tissue-Resident Macrophages

Neutrophils

• Most abundant circulating white blood cells.
• Classified as granulocytes.
• Perform phagocytosis.
• Release antimicrobial substances.
• Important early responders during infection.

Note: Histamine release is primarily associated with mast cells and basophils rather than neutrophils.

Monocytes

• Circulate in the bloodstream.
• Differentiate into:
  • Macrophages
  • Dendritic cells

Mast Cells

Located in connective tissues and mucous membranes.

Involved in:

• Inflammation
• Tissue repair
• Angiogenesis

Release:

• Histamine
• Heparin
• Cytokines

Eosinophils

• Combat parasitic infections.
• Participate in allergic reactions.
• Contain toxic granules.
• Can damage host tissues if overactive.

Basophils

Involved in inflammation and allergic responses.

Release:

• Histamine
• Interleukins

Natural Killer (NK) Cells

• Detect virus-infected and abnormal cells.
• Induce apoptosis.

Release:

• Perforins
• Granzymes

Dendritic Cells

• Professional antigen-presenting cells (APCs).
• Located in tissues that contact the external environment.
• Capture antigens and present them to T cells.
• Activate both innate and adaptive immune responses.
• Function as a bridge between innate and adaptive immunity.

Cell Lineage

Source: Janeway's Immunobiology 9th ed.
All immune cells arise from pluripotent hematopoietic stem cells (HSCs) located in the bone marrow.

Hematopoietic Stem Cells (HSCs)

• Multipotent stem cells that generate all blood cells.
• Found primarily in bone marrow.

Common Lymphoid Progenitor

• Gives rise to the lymphoid lineage, including:
  • B cells
  • T cells
  • Natural killer (NK) cells

Source

Interactive Biology

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