Overview
From Barrier to Targeted Defence
The immune system protects the body from microbes and abnormal cells while normally leaving the body’s own tissues alone.
The immune system protects the body from microbes and abnormal cells while normally leaving the body’s own tissues alone. Its first response is innate: skin, mucous membranes, airway secretions, phagocytes, complement, and inflammation act quickly but without antigen-specific memory. Adaptive immunity follows with B-cell antibody production and T-cell responses. Memory cells allow a faster, stronger response to a later exposure. Inflammation explains many familiar findings. Increased blood flow produces warmth and redness; increased vascular permeability permits fluid and immune cells to enter tissue, causing swelling and sometimes pain. That response is protective when it contains a local threat, but excessive or misdirected inflammation can damage tissue, as seen in severe allergy or autoimmune disease. Vaccination uses adaptive immune memory without requiring the person to experience the target infection. Immunosuppression, marrow disease, certain medications, and some congenital conditions can weaken this response. The result may be recurrent or severe infection, poor vaccine response, or muted clinical signs. A person with impaired immunity may not develop a striking fever even while becoming seriously ill. The immune system can therefore fail in two...