12. Immunity to Infection
• Immunity is the acquired ability to defend
against infection by disease-causing
organisms.
13. Overview of your immune system
• First line of defense: Physical barriers that viruses, bacteria must cross
–
–
skin covers ~2 m2
Mucous membranes that line digestive, respiratory, reproductive tracts cover
~400 m2
• Second line of defense: Innate immune system (germline-encoded
receptors -- no adaptation to specific pathogens)
– Macrophages (Greek for “big eater”), neutrophils, natural killer (NK) cells
• Third line of defense (vertebrates only): Adaptive immune system
(adapts to defend against specific pathogens using variable receptors)
– B cells make antibodies that vary -- can make an antibody specific for any
new antigen
– T cells mediate cellular responses using variable receptors (T cell receptors;
TCRs)