Nonspecific lymphocytes that spontaneously attack and kill cancer cells and cells infected by microorganisms are known as
O antibodies.
O lymphocytes.
O macrophages.
O natural killer cells.

Antibodies.

Explanation:

An antibody is a protein produced by the white blood cells of an organism to resist harmful foreign substances, so-called antigens. Once the body has done this once against an antigen, it will usually develop immunity to the disease that the antigen represents. A common vaccination method is to supply the body with small amounts of unknown antigens, thus stimulating the body to produce anti-inflammatory antibodies.  In some cases, antibodies can react to harmless substances, causing an allergic reaction.