Basic Immunology Lecture 1: Barriers to Infection PDF

# Basic Immunology (Lecture 1) ## Barriers to Infection **College of Medicine** **Al-Maarefa University** ## Immunology: - Study of the immune system and its disorders. ### Basic Immunology ### Clinical Immunology ## Immunity - The main function of immunity is to prevent and fight against: *...

# Basic Immunology (Lecture 1) ## Barriers to Infection **College of Medicine** **Al-Maarefa University** ## Immunology: - Study of the immune system and its disorders. ### Basic Immunology ### Clinical Immunology ## Immunity - The main function of immunity is to prevent and fight against: * Infection caused by different microbes (outside invaders). * Tumors (immune surveillance = scanning of body cells to detect and kill corrupted cells such as tumor cells (inside cellular abnormalities)). ## The immune system has two lines of defense: - **Innate (non-specific) immunity**. - **Adaptive (specific) immunity**. ## Innate Immunity Characters of innate immunity: - **First line of defense.** - **Rapid onset defense**: Present as an intrinsic response since birth. - **Generalized**: The same for all microbes (not specific). - **Limited specificity**. - **No role of memory immune cells** in this response. - **Same response** on re-exposure to antigens. - **Block entry of microbes and eliminate microbes** which succeeded to enter the host. ## Components of innate immunity 1. **Barriers to infection**: (physical, mechanical, chemical and biological barriers). 2. **Innate immune cells**. 3. **Cytokines** (chemical mediators produced by some immune cells and somatic cells). 4. **Acute phase proteins**. 5. **Complement** (alternative, Lectin) pathway. 6. **Phagocytosis**. 7. **Inflammation**. ## Adaptive Immunity Characters: - **Second line of defense.** - **Delayed**: Develops as a response to infection. - **Specific** for each microbe/antigen. - **Stronger immune response** on re-exposure tot the same antigen. - **Depends on memory cells**. ## Components of adaptive immunity: 1. **Adaptive immune cells** (memory T and B cells). 2. **Major blood proteins**: **Antibodies**: Specific. 3. **Complement** (classical) pathway. 4. **Other cytokines**. ## Barriers to Infection: ### A - The Physical Barriers: 1. **Skin**: - The outermost layer of epidermis (stratum corneum) is composed of tightly packed layers of squamous cells which protect against invasion of microbes. - Stratum corneum cells are continuously detached to remove colonizing microbes. 2. **Mucous membranes**: - Lines all of the body's cavities such as the GIT & respiratory tract and the genitourinary system. - This epithelium contains goblet cells that secrete mucus and so traps microbes. ### B - Mechanical Barriers: 1. **Respiratory tract**: - The hair-like rhythmically beating cilia of the epithelia lining the respiratory tract passages remove secretions with trapped microbes. - Mucus production and alveolar macrophage. 2. **Urinary tract**: - Washing of sterile urinary tract by sterile urine during micturition (flashing action of urine). 3. **Eye**: - Washing of eye by tears during eye led movement (blinking). 4. **Intestine tracts**: - Intestinal peristalsis removes microorganisms that can't colonize the intestine. ### C - Chemical Barriers: 1. **Skin**: - **Skin sweat**: * Has acidic pH of 5.5. * Contains **lysozyme**: Splits bacteria peptidoglycan in cell wall. * **Nucleases**(RNases and Dnases) destroy the microbial genetic material (nucleic acid). * **Short unsaturated fatty acids**: Toxic for bacteria. * **Defensins** (Alpha and Beta): Act on bacterial cell membrane. 2. **The stomach and gastrointestinal tract**: - **Saliva** contains **lysozyme**: Splits bacteria cell wall. - The highly acidic environment of stomach (pH of 1 to 3) kills most ingested microbes. - **Defensin (alpha) and cryptidin** destroys pathogens. - The digestive enzymes such as **pepsin**. - **Beta-Defensin** is present in the respiratory tract. 3. **Eye (lacrimal secretions)**: - Tears contain IgA and lysozymes. ### D - Biologic Barriers (commensal microbes = normal flora): - Considered as an important part of natural defense. - Protect human body cavities from colonization with exogenous pathogenic organisms. #### How commensal microbes inhibit pathogenic colonization? 1. - **Production of bacteriocins (antibiotics).** 2. - **Competitive depletion of essential nutrients.** 3. - **Production of toxic by-products** (vaginal lactic acid pH 4). 4. - **Stimulation of natural antibodies.** ## Establishment of Infection: Microorganisms could invade human natural barriers and cause disease considering the following factors: 1. **Pathogenic dose**: - The minimum number of organisms required to establish an infection. 2. **Microbial Verulence**: - Microbial extracellular structures, proteins, enzymes and toxins that increase the microbial pathogenic ability. 3. **Port of Entry**: - Ingestion. - Inhalation. - Direct penetration. 4. **Host Immunity**: - Age extremes have weak immunity. ## Thank you!