29. Innate immunity – factors and mechanisms.

Understanding Immunity

• Immunity refers to the body’s ability to resist and fight against harmful pathogens.
• It is a complex defense system that prevents pathogens from entering the body and eliminates them if they do.
• The immune system includes specialized organs, cells, and molecules working in harmony to maintain health.

Innate Immunity: The Body’s First Line of Defense

• Innate immunity is the body’s natural, non-specific defense mechanism present from birth.
• It does not target specific pathogens but responds broadly to any invader.
• This type of immunity does not improve with repeated exposure to the same pathogen.
• The innate immune response is very fast, usually activated within minutes to a few hours of infection.

External Barriers: Keeping Pathogens Out

Physical Barriers

• The skin acts as a tough physical shield that pathogens cannot easily cross.
• Tears, saliva, and urine mechanically flush out microbes from body surfaces.
• The respiratory tract uses mucociliary clearance where cilia push mucus filled with trapped particles toward the throat to be expelled or swallowed.

Chemical Barriers

• The acidic environment of the stomach and vagina kills many pathogens.
• Lysozymes in saliva, tears, and other secretions break down bacterial cell walls.
• Sudden pH changes from the stomach to the intestines act as additional hostile conditions for microbes.

Biological Barriers

• The body’s natural microbiota (such as gut and vaginal flora) compete with pathogens for space and resources, preventing their colonization.
• These resident microbes may also secrete substances that are toxic to pathogens.

Disruption of Barriers

• Conditions like cystic fibrosis or primary ciliary dyskinesia impair mucociliary clearance, leading to chronic respiratory infections.