How does the human immune system fight off infections?

When pathogens like bacteria or viruses enter the body, the immune system responds in two main ways. The innate immune system acts first, providing a rapid but general response. White blood cells called neutrophils and macrophages detect and destroy invaders by engulfing them, while inflammation helps contain the spread of infection. If the pathogen persists, the adaptive immune system kicks in. B cells produce antibodies that bind to specific pathogens and neutralize them or mark them for destruction. T cells either directly kill infected cells or help coordinate the overall immune response. The adaptive system also creates memory cells, so if the same pathogen appears again, the body can respond faster and more effectively, often preventing illness entirely.