Defending the body against bacterial infection and invasion by other foreign substances is the function of A white blood cells
B platelets
C red blood cells
D plasma

white blood cells

Explanation:

White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from multipotent cells in the bone marrow known as hematopoietic stem cells.

answer; indirect elisa;