How do plants, invertebrates, and vertebrates respond to pathogens?

Plant defenses against pathogens include molecular recognition systems with systemic responses, where an infection triggers chemical responses that destroy infected and adjacent cells, minimizing possibility of spreading the pathogen.

Invertebrates have a large variety of immune responses. Many invertebrates have a thick layer of skin or shells for protection. Some secrete mucus, which can trap invaders.

Vertebrates have innate and adaptive response systems. The innate systems, such as macrophages (a type of white blood cell), skin, and mucus, attack invaders indiscriminately. Pathogens intercepted by macrophages and dendritic cells have their surface antigens presented on the outside of these cells. These Antigen Presenting Cells help B and T-cells recognize that an attack is underway.