The human body is constantly exposed to pathogenic microorganisms such as bacteria, viruses, fungi, and parasites present in the environment. To survive, the body relies on an integrated network of physiological responses known as immune defence mechanisms. These defenses prevent pathogen entry, contain localized infections, and destroy established invaders. Immunology divides these responses into two primary categories: innate immunity, which provides immediate, non-specific protection present from birth, and adaptive immunity, which mounts targeted, antigen-specific responses with immunological memory.
The first line of defense consists of physical, chemical, and biological barriers that block pathogen entry into body tissues.
When pathogens breach surface barriers, internal innate mechanisms activate immediately. Phagocytic cells, including macrophages and neutrophils, engulf and digest foreign particles through phagocytosis. Natural killer cells patrol the body, targeting virus-infected host cells and tumor cells by inducing apoptosis. Antimicrobial proteins such as the complement system circulate in the blood, tagging pathogens for destruction and puncturing microbial cell membranes.
Inflammation is a localized tissue reaction triggered by injury or infection, characterized by redness, heat, swelling, and pain. Mast cells stationed in tissues release histamine and other inflammatory mediators when stimulated. These chemicals cause local vasodilation, increasing blood flow and vascular permeability. This vascular change allows plasma proteins and white blood cells to leak into the interstitial space, isolating the injury and initiating tissue repair.
Adaptive immunity provides tailored protection against specific foreign antigens and develops memory cells for long-term protection. This branch relies on lymphocytes originating from bone marrow. B lymphocytes mature in the bone marrow and drive humoral immunity by differentiating into plasma cells that secrete antibodies. T lymphocytes mature in the thymus and drive cell-mediated immunity, directly destroying infected cells or helping regulate other immune cells.
Numerous physiological and environmental variables influence a patient's ability to mount an effective immune response. Malnutrition depresses immune function by limiting protein synthesis needed for antibody and cell production. Chronic stress elevates cortisol levels, which suppresses lymphocyte proliferation and inflammatory cytokine production. Extremes of age, particularly in neonates and older adults, exhibit decreased immune responsiveness. Furthermore, immunosuppressive medications and chronic illnesses like diabetes impair leukocyte activity.
Nurses play a critical role in identifying compromised immune systems and preventing nosocomial infections. Assessment involves monitoring vital signs for subtle trends like low-grade fevers, inspecting skin integrity, and reviewing laboratory results like total white blood cell and neutrophil counts. For immunocompromised patients, standard precautions must be strictly combined with protective isolation measures to minimize exposure to opportunistic environmental pathogens.