Chapter 14 Microbiology

An Introduction to Host Defenses

Functions of the Immune System

• surveillance of body

• recognition of foreign material

• destruction of foreign entities

Innate defenses

present at birth, provide nonspecific resistance to infection

Adaptive immunity

specific, must be acquired

First line of defense

any barrier that blocks invasion at the portal of entry (usually physical)

Specificity of the first line of defense

non-specific

Second line of defense

protective cells and fluids; inflammation and phagocytosis

Specificity of the second line of defense

non-specific

Third line of defense

acquired with exposure to foreign substance; produces protective antibodies and creates memory cells

Specificity of the third line of defense

specific

Examples of the first line of defense

• physical barriers: skin, tears, mucus, coughing, sneezing

• chemical barriers: low pH, lysozymes, digestive enzymes

• genetic barriers: inherent resistance

Examples of the second line of defense

phagocytosis, inflammation, fever

Examples of the third line of defense

Immune cells (B and T lymphocytes, antibodies)

Type of membrane that lines the respiratory, digestive, reproductive, and urinary systems

Mucous membrane

Defense of the respiratory tract: First line

• mucous

• nasal hair

Lysozymes

enzyme that hydrolyzes the cell wall of bacteria

Lysozymes can be found in

tears

Sweat has a high concentration of

lactic acid and electrolytes

The skin’s pH leans more towards

acidic

In females, vagin a pH leans more towards

acidic

Genotype that provides immunity for people from malaria is best described as

heterozygous

Scientific name for malaria

Plasmodium falciparum

People lacking the Duffy blood group antigen cannot be infected with this disease

malaria (plasmodium falciparum)

Antigens

a substance that induces the production of antibodies- that is recognized as non-self by the immune system.

Example of antigen in microbiology

LPS on gram negative bacteria

Antibodies

proteins secreted by our immune cells that bind antigens

Types of white blood cells (WBCs)

leukocytes, lymphocytes

Leukocytes utilize this kind of immunity

innate immunity

Lymphocytes utilize this kind of immunity

adaptive immunity

Pathogen-associated patterns (PAMPs)

molecules shared by microorganisms

Pathogen recognition receptors (PRRs)

receptors on WBCs (ex. Neutrophils and macrophages) or epithelial cells for PAMPs, ex. Toll-like receptors (TLR)

Function of albumins in blood

regulate viscosity and osmolarity of the blood

Function of globulins in blood

including classes of antibodies

Function of fibrinogens in blood

clotting proteins

Functions of ions in blood

regulate pH and osmotic balance

Hematopoietic stem cells can develop into

• common lymphoid progenitor

• common myeloid progenitor

Common lymphoid progenitors develop into these immune cells

B and T lymphocytes

Common myeloid progenitors develop into these immune cells

• basophils, neutrophils, eosinophils (granulocytes)

• monocytes

Hematopoiesis

process to create RBCs

Stem cells

undifferentiated cells, precursor of new cells

Totipotent stem cells

can become any cell in the body

Totipotent stem cells can be found in

embryos

Multi-potent stem cells

can give rise to a limited number of cell types

Example of multi-potent stem cells

hematopoietic stem cells

Range of neutrophils

55-90%

First immune cell to arrive at site of infection

neutrophils

Range of eosinophils

1-3%

Eosinophil function

target eukaryotic pathogens, such as parasitic worms

Range of basophils

0.5%

Basophil function

release potent chemical mediators and IgE (antibody) in allergy responses

Immunoglobin associated with allergic responses

IgE

Function of mast cells

attract phagocytes to the site of infection

Range of monocytes, macrophages, and dendritic cells

3-7%

Examples of agranulocytes

• monocytes

• macrophages

• dendritic cells

Monocyte

earliest stage, pre-curser cell type to macrophages & dendritic cells

What describes the phagocytic capabilities of monocytes

less phagocytic

If an agranulocyte has higher phagocytic capabilities, that means

it can present antigens more efficiently

What describes the phagocytic capabilities of macrophages

more phagocytic

What describes the phagocytic capabilities of dendritic cells

highly phagocytic

Macrophages

final differentiation of monocytes

Range of lymphocytes

20-35%

Type of immunity for Natural Killer T cells

innate immunity

Function of Natural Killer T cells

kill pathogen infected host cells

Type of immunity for B and T lymphocytes

adaptive immunity

Type of adaptive immunity for B lymphocytes

humoral immunity

Type of adaptive immunity for T lymphocytes

cell-mediated immunity

Cytolytic T cells

kill foreign cells

Helper T cells

modulate immune functions

Site where erythrocytes are developed

bone marrow

Platelets

formed elements in circulating blood that are not whole cells

Functions of lymphatic system

1. Provides an auxiliary route for return of extracellular fluid to the circulatory system

2. drain-off system for the inflammatory response

3. renders immune surveillance, recognition, and protection against foreign material by trafficking immune cells

Areas where lymphatic capillaries don’t permeate

CNS, bone, placenta, thymus

Function of primary lymphatic organs

generates the lymphocytes and early immune cells

Examples of primary lymphatic organs

red bone marrow, thymus gland

Function of secondary lymphatic organs

site of educating lymphocytes and immune cells

Examples of secondary lymphatic organs

lymph nodes, spleen

Some of this type of white blood cells mature in red bone marrow

B cells

Thymus gland

Bilobed gland found in the thoracic cavity superior to the heart

Site of T cell maturation

thymus gland

Areas of body where lymph nodes are common

Armpit, neck, groin area

Lymph nodes are usually filled these kinds of immune cells

agranulocytes (B/T cells, macrophages, dendritic cells)

Spleen

• In the upper left region of the abdominal cavity

• Structurally similar to lymph node; filters circulating blood to remove worn out RBCs and pathogens

Gut associated lymphoid tissue (GALT)

specialized lymphoid tissue in the gastrointestinal tract to increase rate of processing intestinal antigens

This line of defense initiates inflammation

second line of defense

Steps to second line of defense

1. Recognition by innate immune cells

2. Initiate Inflammation

3. Phagocytosis of foreign microbe or infected cells

4. Complement to increase phagocytosis and lyse

microbial membranes

5. Interferon to alert a specific immune attack

Recognition by innate immune cells

• Pattern Recognition Receptors (PRRs)

• Binds Pathogen associated molecular patterns (PAMPs)

• Cells expressing PRRs then will secrete cytokines & chemokines, chemical signals to alert the immune system

Cytokines

alert the immune system to distinguish the type of infection

• ex: tumor necrosis factor

Chemokines

chemical signal that will induce chemotaxis or trafficking of immune cells to the site of infection

• ex: IL-8 will induce the migration of neutrophils

Inflammatory Response

signs and symptoms include:

• redness: increased circulation and vasodilation in injured area

• warmth: heat given off by blood flow

• swelling: fluid escaping into tissue; edema, WBCs, debris, etc

• pain/soreness: stimulation of nerve endings

Diapedesis

migration of cells out of blood vessels into the tissues

What initiates fevers

pyrogens targeting hypothalamus

Exogenous pyrogens

products of infectious agents

Endogenous pyrogens

liberated by monocytes, neutrophils, and macrophages during phagocytosis; interleukin-1 (IL-1) and tumor necrosis factor (TNF)

Benefits of fever

• Inhibits multiplication of temperature- sensitive microorganisms

• Impedes nutrition of bacteria by reducing the available iron

• Increases metabolism and stimulates immune reactions and protective physiological processes

Which immune cells are phagocytic?

Macrophages, neutrophils, and dendritic cells

Functions of the Complement System

1. recruit phagocytes by binding to pathogens

2. work with antibodies to opsinize pathogen surfaces and cause phagocytosis

3. working together complement proteins 1-9 to form a membrane attack complex

Opsonization

binding of antibodies or complement proteins to the surface of infected cells or directly to the microbes

Membrane attack complex

• pore that is formed upon activation via complement

• made in cell membrane of pathogens

• results in lysis

Types of complement pathways

• classic

• lectin

• alternative

Classic complement pathway

activated by the presence of antibody (made by plasma B cells) bound to microorganism

Lectin complement pathway

nonspecific reaction of a host serum protein that binds mannose (sugar) on bacterial surface