The immune system is a complex network of cells, tissues, and organs that work together to defend the body against invading pathogens, such as bacteria, viruses, and fungi, which can cause infections. Here is a simplified explanation of how the immune system works:

1. Recognition of pathogens: The immune system uses various receptors on its cells to recognize the presence of foreign substances, such as antigens on the surface of bacteria and viruses.
2. Activation of immune cells: Once the pathogens are recognized, immune cells, such as white blood cells called T cells and B cells, are activated. T cells can directly kill infected cells, while B cells produce antibodies, which are proteins that specifically target the antigens on the surface of pathogens.
3. Production of memory cells: After a successful response to an infection, some immune cells become memory cells. These cells can quickly respond to subsequent infections with the same pathogen, enabling a faster and stronger immune response.
4. Regulation of the immune response: The immune response is regulated by various factors, such as cytokines and other signaling molecules, to prevent overactive responses that can harm healthy tissues and to ensure that the response is targeted to the specific pathogen.

This is a basic overview of the immune system and how it works. It is a complex and dynamic system that is constantly adapting to new threats and can be influenced by various factors, such as age, genetics, lifestyle, and exposure to pathogens.