Key Terms
Pathogen
Agent (usually a microorganism) that causes disease in a host.
Host
Organism invaded and often harmed by a pathogen. Antigen: foreign or "non-self" macromolecule that triggers the immune r
Epitope
The specific small region of an antigen recognized by antibodies or T and B cells; also called the antigenic determinant
Skin
Continuous barrier; kills/inactivates pathogens via desiccation and acidity. Beneficial microorganisms also compete with
Eyes and mucous membranes
Tears and mucus trap and flush pathogens.
Nasal passages/respiratory tract
Cilia push mucus containing pathogens out of the body.
Stomach
Low pH inhibits pathogen growth. Urinary tract: urination flushes pathogens out.
PAMPs (Pathogen-Associated Molecular Patterns)
Molecular "signatures" on pathogens (carbohydrates, polypeptides, nucleic acids) that differ from host molecules. The im
PRRs (Pattern Recognition Receptors)
On macrophages and dendritic cells; bind PAMPs and trigger response.
TLRs (Toll-like Receptors)
A specific type of PRR; one of the most ancient immune components; present in invertebrates and vertebrates; also found
Macrophage
Large phagocytic cell that engulfs foreign particles; recognizes PAMPs via PRRs.
Monocyte
White blood cell that circulates in blood and lymph; differentiates into macrophages after moving into infected tissue.
Dendritic cell
Binds pathogen signatures; promotes engulfment and destruction; also functions as an antigen-presenting cell (APC).
Cytokine
Chemical messenger that regulates cell differentiation, proliferation, and gene expression to drive immune responses. At
Interleukins (ILs)
Mediate interactions between leukocytes; bridge innate and adaptive responses.