The immune system defends the body against infections and diseases. It consists of white blood cells, antibodies, the lymphatic system, the spleen, the thymus, and bone marrow. These components work together to recognize and neutralize pathogens like bacteria, viruses, and parasites. The immune system has two main parts: innate immunity, which provides immediate defense, and adaptive immunity, which develops targeted responses to specific threats, providing long-lasting protection through memory cells.