How does your immune system recognize and fight infections?

Your immune system uses two main lines of defense. The innate immune system responds immediately and nonspecifically, using physical barriers like skin, plus cells like neutrophils and macrophages that engulf and destroy pathogens. These cells recognize broad patterns on foreign invaders called pathogen-associated molecular patterns using receptors like toll-like receptors. The adaptive immune system kicks in over days and is highly specific. B cells produce antibodies that bind to unique proteins called antigens on pathogens, neutralizing them or marking them for destruction. T cells either kill infected cells directly or coordinate the broader immune response. Crucially, the adaptive system creates memory cells, so if the same pathogen returns, the response is faster and stronger, which is also the principle behind vaccination.