The cell's defense system against infection is called the immune system. This complex network of cells, tissues, and organs works together to identify and eliminate foreign pathogens, such as bacteria and viruses. Key components of the immune system include white blood cells (lymphocytes), antibodies, and the spleen. The immune response can be categorized into innate immunity, which provides immediate protection, and adaptive immunity, which develops over time and provides long-lasting defense against specific pathogens.