Resistance
Ability to ward off disease
Susceptibility
Lack of resistance to a disease
Nonspecific resistance
Defenses against any pathogen
Specific resistance
Immunity, resistance to a specific pathogen
First line of defense
- Skin membranes
- Normal microbiota
Second line of defense
- Phagocytes
- Inflammation
- Fever
- Antimicrobial substances
Mechanical Factors: Skin
- Tightly packed cells in epidermis packed with keratin
- Shedding of skin and microbes
Mechanical Factors: Mucous Membranes
- Not as effective as skin
- Cilliary escalator: Microbes trapped in mucous and transported away from the lungs
- Lacrimal apparatus: washes eye
- Saliva: washes microbes off
- Urine and Vaginal secretions: flow out
Chemical Factors: Skin
- Fatty acid in sebum (low pH of 3-5)
- Lysozyme: perspiration, tears, saliva, tissue fluids
- Gastric juice (low pH of 1.3-3.0)
- Transferrins in blood find iron
Microbial antagonism/Competitive exclusion
Normal microbiota with pathogens
Phagocytosis
- Ingestion of microbes/ particles by a cell
- Performed by phagocytes
Leukocytes
White blood cells
Granulocyte
Large granules in cytoplasm visible under a light microscope
Agranulocyte
Have granules, but not visible under light microscope
(Nonsensical naming)
Types of Granulocytes
- Neutrophils (60%-70%)
- Basophils (0.5%-1%)
- Eosinophils (2%-4%)
Neutrophils
- "First responders at crime scene"
- Highly phagocytic and motile
- Leave blood, enter tissue that is infected and destroys microbes and foreign particles
Basophils
- Role is unclear
- Release histamine
Eosinophils
- Attach to outer surface of parasites and discharge peroxide ions that destroy them
Types of Agranulocytes
- Monocytes
- Lymphocytes
Monocytes
- "Detective if first responders can't handle it"
- Phagocytic as mature macrophage
Lymphocytes
- "Military, the last defense, most strong and most harmful"
- T cells and B cells
- Are not phagocytic
- Key role in specific immunity
Differential White Cell Count
% of each type of WBC in a sample of 100 WBC
Action of Phagocytic cells
- Neutrophils and monocytes will migrate to infected area
- Granulocytes dominate initially
- Monocytes mature into macrophages and dominate after progression of infection
Chemotaxis
- Chemical attraction
- Microbial products
- Components of WBC
- Peptides from complement
Adherence
- Attachment of MO
- M proteins and capsules prohibit attachment
- Opsonization: enhancement of phagocytosis by coating with certain proteins
Inflammation
- Redness
- Swelling
- Heat
- Pain
Vasodilation
- Increased blood flow
- Increased permeability of BV
- Prostaglandins & Leukotrienes
Margination
Phagocytes stick to inner surface of BV
Emigration
Diapedisis-Phagocytes move out of BV and into tissues
Fever
- Above 37 C
- Hypothalamus releases prostaglandins to set high temp
- Body increases metabolism
- Gram - endotoxin cause phagocytes to release interleukin 1
- When IL-1 is eliminated, body temp falls
Advantages of fever
- Increased productivity of T-lymphocytes
- Increased effect of interferons
- Increased tissue repair
Anti-Microbial Substances
- Complement
- Phagocytosis
- Interferon
Complement System
Three PWs
- Classical
- Alternative
- Lectin
Serum proteins involved in lysis and phagocytosis of bacteria
Interferons
- Interfere with viral multiplication
- Host cell specific but not virus specific
- Disadvantages: only effective for short periods of time, when injected there are serious and sometimes toxic side effects, does not affect cells already infected