Leukocytes, commonly known as white blood cells, are a crucial part of the immune system. They help the body fight infections and diseases by identifying and attacking harmful pathogens like bacteria and viruses. There are several types of leukocytes, including neutrophils, lymphocytes, and monocytes, each with specific functions in immune response. These cells are produced in the bone marrow and can be found in the bloodstream and lymphatic system. A healthy leukocyte count is essential for maintaining good health, as low levels can lead to increased susceptibility to infections, while high levels may indicate an underlying health issue.