Also called leukocytes, these nearly colorless blood cells defend the body against infection
[DOC] [TLE] The Immune System - Dictionary definition of The Immune System ... [PAR] These substances include bacteria, viruses, and other infection-causing 
parasites ... system is extremely effective in performing its work of defending the 
body, but ... Lymphocytes, a type of white blood cell, are concentrated in the 
lymph nodes, .... protecting the body against invaders