Innate and Adaptive Immunity

Key points

• • Innate immunity is the body's earliest and fastest defence, present from birth; it recognises broad classes of invader and gives a rapid, broadly targeted response with little lasting memory.
• • It includes barriers (skin and mucus), phagocytic cells (neutrophils and macrophages), natural killer cells, the complement system and the inflammatory response.
• • Adaptive immunity is slower on first exposure but uses highly specific antigen receptors and develops memory, so a second exposure brings a faster and stronger response.
• • Adaptive immunity has two arms: cell-mediated immunity carried out by T cells, and humoral immunity carried out by antibodies from B cells.
• • Helper T cells coordinate the response, cytotoxic T cells kill infected cells, and B cells become plasma cells that secrete antibodies.
• • Memory cells left behind after an infection or a vaccine give long-lasting protection, which is the basis of immunisation.