The immune system is composed of diverse cells that arise primarily from hematopoietic stem cells in the bone marrow and function together to defend the body against pathogens while maintaining self-tolerance. These cells are broadly classified into innate and adaptive immune cells based on their mechanisms of recognition and response. Cells of the innate immune system provide immediate, non-specific defense. Neutrophils are the most abundant circulating leukocytes and act as first responders by phagocytosing microbes and releasing antimicrobial enzymes and reactive oxygen species. Eosinophils participate mainly in defense against parasitic infections and contribute to allergic reactions through the release of cytotoxic granules. Basophils and mast cells play central roles in inflammation and hypersensitivity reactions by releasing histamine and other mediators upon activation. Monocytes circulate in the blood and differentiate into macrophages and dendritic cells when they migrate into tissues. Macrophages are professional phagocytes that engulf pathogens, remove