Immune cells are a diverse set of specialized cells that detect, respond to, and remember threats such as viruses, bacteria, parasites and cancer cells. They arise from stem cells in the bone marrow and can be broadly grouped into innate and adaptive populations.

Innate immune cells act quickly and non specifically. Neutrophils are rapid responders that engulf and destroy microbes, often being the first cells to reach an infection site. Macrophages patrol tissues, clear debris and pathogens, and release signaling molecules that shape inflammation. Dendritic cells capture antigens and present them to other immune cells, forming a critical bridge to adaptive responses. Natural killer cells recognize and kill virus infected and abnormal cells without prior sensitization.

Adaptive immune cells provide targeted and long lasting protection. B cells produce antibodies that bind specific antigens, neutralize pathogens and mark them for destruction. T cells include helper T cells that coordinate immune responses through cytokines and cytotoxic T cells that directly kill infected or malignant cells. Both B and T cells form memory subsets, enabling faster and stronger responses upon re exposure to the same threat.

Regulatory mechanisms are essential to prevent excessive or misdirected activity. Regulatory T cells and certain macrophage states can dampen responses and help maintain tolerance to self tissues. When regulation fails, immune cells can drive autoimmunity, chronic inflammation or allow tumors to evade attack.

Modern research tracks how distinct immune cell states and interactions define health and disease, revealing targets for vaccines, immunotherapies and treatments for inflammatory and autoimmune conditions.