The immune system is the body's defense mechanism against infections and diseases. It consists of various cells, tissues, and organs that work together to identify and eliminate harmful pathogens like bacteria, viruses, and parasites. Key components include white blood cells, lymph nodes, and the spleen, which all play crucial roles in recognizing and responding to threats. When the body encounters a pathogen, the immune system activates to produce specific responses. This includes the production of antibodies, which are proteins that target and neutralize invaders. A well-functioning immune system is essential for maintaining overall health and preventing illness.