The immune system protects the body from harmful pathogens like bacteria and viruses by recognizing, fighting, and remembering them. It has three lines of defense. The first line includes barriers like skin and mucous membranes that keep germs out. The second line is the innate immune response, which reacts quickly with things like inflammation, fever, and immune cells that attack invaders. The third line is the adaptive immune response, which is more specific and uses B cells and T cells to target pathogens and create memory for faster responses in the future. Leukocytes, or white blood cells, each have different roles in this process. Neutrophils and monocytes help destroy pathogens, eosinophils fight parasites, and basophils trigger inflammation. Lymphocytes include B cells that make antibodies, helper T cells that activate other cells, cytotoxic T cells that kill infected cells, regulatory T cells that control the response, and natural killer cells that attack infected or abnormal cells. All of these parts work together to keep my body healthy.