Which body systems are directly responsible for regulating these nodes and protecting the body from harmful materials in tissue fluid?

The body systems are directly responsible for regulating these nodes and protecting the body from harmful materials in tissue fluid are the immune and lymphatic systems. Lymphatic is a network of tissues and organs that help rid the body of toxins, waste, and other unwanted materials. The immune system on the other hand is the system that prevents the invasion of pathogens causing diseases to the body. 

Centration is the correct answer