Final answer:
Lymphocytes, including T cells, B cells, and natural killer cells, form the foundation of the immune system, with T cells targeting infected or abnormal cells, B cells producing antibodies, and natural killer cells providing innate immunity against various threats.
Step-by-step explanation:
The white blood cells (WBCs) that form the foundation of the immune system are primarily the lymphocytes, which include T cells, B cells, and natural killer cells. Lymphocytes are integral to the body's immune response. T cells play a critical role in the cell-mediated immune response, targeting infected cells with viruses, fungi, bacteria, and protecting against cancer cells and transplanted tissues. B cells are responsible for producing antibodies and inactivating bacterial toxins, whereas natural killer cells provide a nonspecific defense against viruses, certain cancer cells, and cells with abnormal markers.