E. Even urine with its low pH helps protect the urinary tract. Second Line of Defense -Nonspecific Responses B. First on the Front Lines 1. For example Neutrophils are leukocytes which become amoeba-like and ingest and digest bacteria. Macrophages engulf many foreign agents and do so repeatedly with a big appetite. C. Inflammation 1.
Physical signs are redness, swelling, heat, pain, and changes in capillary permeability.
Third Line of Defense -The Immune System A. Overview of Immune Responses 1. Sometimes physical barriers and inflammation may not be sufficient to overwhelm the invader. The vertebrate immune system is a complex interaction of white blood cells called B and T lymphocytes. B cells are lymphocytes that produce antibodies. Y-shaped antibodies become embedded in B cell cell membrane.