Innate Immunity Defense Barriers

Study Notes

Innate immunity has multiple defense barriers
First Line: Physical and chemical barriers like skin, mucosal tissues (respiratory, digestive, urogenital), and glandular tissues (salivary, lacrimal, mammary)
Second Line: Cellular immune responses triggered by receptors recognizing pathogen components. White blood cells engulf and destroy microbes via phagocytosis. Cells produce antimicrobial substances and cytokines/chemokines to recruit cells and create inflammation.
Third Line: Dendritic cells present pathogens to lymphocytes, triggering adaptive immunity.

Examples of mechanisms and their functions:
- Skin and mucous membranes: retard microbe entry
- Lactic acid: inhibits microorganism growth
- Cilia: remove pathogens from respiratory tract
- Stomach acid (low pH): prevents pathogen growth
- Urine: flushes pathogens from the body
- Lysozyme: attacks pathogen cell walls
- Normal flora: competes with pathogens, produces antimicrobial peptides
- Cells: participate in phagocytosis (e.g., NK cells destroying target cells)
- Pathogen recognition receptors (PRRs, e.g., Toll-like receptors): assist phagocytic cells in recognizing pathogens.

Adaptive (or acquired) immunity is a specific system protecting the body from microbes and abnormal cells. It's activated by foreign substances.
Characteristics:
- Specific: for individual pathogens
- Systemic: immunity isn't limited to infection site
- Memory: increased response to repeated exposure to the same pathogen.

Comparison of Natural and Adaptive Immunity:

Feature	Natural Immunity	Adaptive Immunity
Specificity	Non-specific	Specific
Response Time	Rapid (minutes to hours)	Slow (days to weeks)
Memory	No	Yes
Soluble Components	Antimicrobial peptides and proteins	Antibodies
Major Cell Types	Phagocytes, NK cells, dendritic cells	T cells, B cells, APCs (antigen-presenting cells)