The document summarizes how the immune system responds to pathogens. It explains that white blood cells identify and eliminate pathogens through antibodies and an immune response. The immune system includes organs like the thymus, bone marrow, tonsils, spleen and lymph nodes that produce white blood cells. Pathogens are recognized through antigens that trigger an antibody response. Multiple types of white blood cells like macrophages and lymphocytes then work together through several steps to identify, attack and remember the pathogen to build immunity.