How Does the Immune System Work?

The human immune system is a multi-layered defence network. The innate immune system provides the first response: physical barriers (skin, mucous membranes), chemical defences (stomach acid, antimicrobial enzymes), and immune cells (neutrophils, macrophages, natural killer cells) that attack invaders within minutes to hours without specificity. If the innate system cannot contain the threat, the adaptive immune system activates over days: T cells and B cells recognise specific antigens on the pathogen, mount a targeted attack, and create memory cells for future encounters. This two-system design balances rapid general defence with precise, long-lasting protection.