Introduction to innate Immunity in Human

Innate immunity is the body’s first line of defense against infections. It provides immediate, non-specific protection against a wide range of pathogens such as bacteria, viruses, fungi, and parasites. Unlike adaptive immunity, it does not rely on prior exposure or memory.

1. Pir Mehar Ali Shah Arid Agriculture University Rawalpindi Submitted by: Laraib Saleem & Hajra Bi Submitted to: Mam Aniee Class: BS Biology (Semester 5) Arid No: 23-Arid-1898 Subject: Microbiology

2. Innate Immunity

3. Innate Immunity Overview Also called natural resistance; acts nonspecifically in early immune response Recognizes pathogens through pattern recognition receptors (PRRs) PRRs detect pathogen-associated molecular patterns (PAMPs) PAMPs are unique to microbes, absent in host tissues Activates nonspecific immune cells, leading to pathogen clearance Initiates adaptive immune response activation Innate immunity: first line of defense, external and internal components Preformed, standardized, without memory, relatively nonspecific

4. External Innate Immunity: Natural Barriers Prevents pathogen penetration at body contact points Intact skin blocks most pathogens (exceptions: Treponema pallidum, Schistosoma mansoni) Skin secretes lactic acid, fatty acids lowering pH (bacteriostatic) Tears protect eyes physically and contain lysozyme against Gram-positive bacteria Mucus and ciliated epithelium in respiratory tract filter pathogens Stomach acidity kills organisms; normal flora inhibits pathogen attachment Similar protective mechanisms in urogenital tract

5. Internal Innate Immunity: Protection Inside the Body Activated when pathogens breach external defenses Main mechanisms: physiologic barriers, phagocytosis, inflammation

6. Physiologic Barriers Body temperature and oxygen tension inhibit pathogen growth Example: Chickens resist anthrax due to high body temperature Complement proteins cause cell lysis and boost phagocytosis Interferons inhibit viral replication in infected and neighboring cells

7. Phagocytosis in Innate Immunity Key defense through engulfing and destroying pathogens Conducted by mononuclear phagocyte system (monocytes, macrophages) Macrophages release cytokines (TNF-alpha, IL-1, IL-6) that trigger inflammation Neutrophils phagocytize microbes but do not present antigens Neutrophils produce defensins and cathelicidins with antimicrobial activity Dendritic cells clear infections and present antigens to T lymphocytes (link to adaptive immunity)

8. Additional Innate Immune Cells: NK and NKT Cells Natural killer (NK) cells kill virus-infected and tumor cells without prior exposure NK cells produce cytokines (interferon-y, TNF-a) activating other immune cells Natural killer T (NKT) cells combine NK and T cell functions, responding rapidly

9. Inflammation: Internal Innate Defense Mechanism Triggered by pathogen insult and chemical mediators Signs: redness, swelling, heat, pain, loss of function Involves clotting, increased blood flow, capillary permeability, and phagocyte influx Serves as a defense mechanism and tissue repair initiator

10. Innate and Adaptive Immunity Relationship Innate immunity acts rapidly to control infection If innate response fails, adaptive immunity activates later with specificity and memory Both systems cooperate: innate reduces workload, adaptive enhances effectiveness

11. Summary The immune system has two main functions: a. Recognition and defense against foreign substances. b. Immunosurveillance . Components of innate immunity are preformed, standardized, without memory, and nonspecific. Internal defenses: Temperature, Oxygen tension, phagocytosis, inflammation. Major cells: Neutrophils, macrophages, dendritic cells, NK cells, and NKT cells. Innate immunity sets the stage for adaptive immunity.