White blood cells, also known as leukocytes, are a common component of both blood and lymph.

• White blood cells: These cells are made in the bone marrow and help the body fight infection. They are a key part of the immune system's reaction to foreign substances in the body. 

• Lymph: This fluid is similar in composition to blood plasma and is derived from it. It contains lymphocytes, which are a type of white blood cell. Lymph is part of the lymphatic system, which helps the body defend itself.