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