Overview of the Immune System

Immune System

Network of cells, tissues, organs, & soluble factors that work together to protect the body from invading pathogens

Humoral components are found in the…

blood plasma

Cellular components are found in the…

buffy coat (WBCs)

Humoral components of the immune system

Proteins & glycoproteins: antibodies, complement, cytokines

Cellular components of the immune system

WBCs: neutrophils, lymphocytes, monocytes, basophils, eosinophils

Key immune organs

-Thymus -Lymph nodes -Spleen -Bone marrow

Immunology

Study of immune system, immune response to infectious diseases/tumors, & diseases that occur as a result of inadequate functioning of the immune system

3 layers of defense in the body

1. Physical, chemical, & microbiological barriers
2. Innate immunity
3. Adaptive immunity

Mechanical barriers of the skin

-Epithelial cells joined by tight junctions -Longitudinal flow of air or fluid

Mechanical barriers of the gut

-Epithelial cells joined by tight junctions -Longitudinal flow of air or fluid

Mechanical barriers of the lungs

-Epithelial cells joined by tight junctions -Movement of mucus by cilia

Mechanical barriers of the eyes, nose, & oral cavity

-Epithelial cells joined by tight junctions -Tears -Nasal cilia

Chemical barriers of the skin

-Antimicrobial peptides -Fatty acids

Chemical barriers of the gut

-Antimicrobial peptides -Low pH -Antimicrobial enzymes

Chemical barriers of the lungs

-Antimicrobial peptides -Pulmonary surfactant

Chemical barriers of the eyes, nose, & oral cavity

-Antimicrobial peptides -Antimicrobial enzymes in tears & saliva

Microbiological barriers of the skin, gut, lungs, & eyes, nose, & oral cavity

Normal microbiota

Epithelial tissue

A body tissue that covers all internal and external surfaces of the body

What firmly attaches epithelial cells to one another, forming a barrier?

tight junctions

Epithelial cells continuously…

shed & replace

Impaired barrier function in the respiratory tract

-Impaired mucus production (dehydration) -Impaired ciliary function (primary ciliary dyskinesia, infectious agents causing damage to cilia, environmental toxicants)

Impaired barrier function in the GIT

-Impaired peristalsis (post-sx, torsion) -Epithelial damage (ulceration) -Microbiota imbalance (antibiotic therapy, dietary changes)

Impaired barrier function in the eye

Epithelial damage (corneal abrasions, ectopic lashes, dry eye/KCS)

Impaired barrier function in the skin

-Epithelial damage (wounds, lacerations, ulcers, sx, IVC) -Excessive washing - removes fatty acids -Atopic/allergy dermatitis

Innate immunity key components

phagocytes, complement, & cytokines

The activation of innate immune components leads to…

inflammation

Key components of the adaptive immunity

Antibodies (humoral immunity) T cells (cell-mediated immunity)

The activation of adaptive immune components leads to…

memory response

Relationship between innate and adaptive immunities

Innate is required to activate adaptive and adaptive enhances mechanisms of innate

What is the key difference between the innate and adaptive immune systems?

The way that pathogens are recognized

Pathogen recognition in innate immune cells

Have receptors that recognize common molecular features of groups of pathogens & damaged host cells or tissue

Pathogen recognition in adaptive immune cells

Have receptors that recognize unique molecular features of each different pathogen

Speed of response in innate immunity

Rapid (inborn)

In innate immunity, pathogens/damaged cells are recognized through…

cellular receptors and soluble serum proteins

Innate immunity destroys cells through…

innate immune cells and soluble components

Receptor-mediated responses by cells

1. Signal perception via ligand binding to receptor
2. Intracellular signal transduction
3. Cellular response

Innate immunity cells

-Neutrophils -Monocytes -Macrophages -Mast cells -Eosinophils -Basophils -Dendritic cells -NK cells

Innate immunity soluble factors

-Complement -Cytokines -Interferons

Roles of the innate immune system in pathogen defense

-Control infection during time needed to engage adaptive immune system -Activates & directs adaptive immune system

Adaptive immune cells

-B lymphocytes -T lymphocytes

Adaptive immune soluble factors

-Antibodies -Cytokines

Speed of adaptive immunity

Delayed response - at least 5 days to develop response to a pathogen for the first time

Specificity of adaptive immunity

Highly specific to the pathogen-derived antigens

Antigen recognition in adaptive immunity is done by…

antigen-specific receptors of B & T lymphocytes

Antibodies & activated T cells perform what function?

mediate destruction of pathogen

Development of B & T memory cells allows…

generation of a rapid and effective response if that same antigen is ever re-encountered

Antigen

Molecule that is specifically recognized by B or T cell antigen receptors

Types of pathogens

-Bacteria -Fungi -Viruses -Parasites

Extracellular pathogens

Present outside the cell

Intracellular pathogens

Present within the cell (viral replication)

Bacteria

Single cell prokaryotes

2 types of bacteria

gram positive and gram negative

Cell wall of gram positive bacteria

Thick peptidoglycan layer around cytoplasmic membrane

Staining of gram positive bacteria

Retains stain upon treatment with alcohol or acetone

Examples of gram positive bacteria

Clostridium, Staphylococcus, Streptococcus

Cell wall of gram negative bacteria

thin peptidoglycan layer around cytoplasmic membrane and outer membrane with LPS

Staining of gram negative bacteria

Loses stain upon treatment

Examples of gram negative bacteria

E. coli, salmonella, bordetella

Capsule

Protective outermost layer of polysaccharide surrounding some bacteria

Fungi

Eukaryotic pathogens

2 forms of fungi

Yeasts (unicellular) & molds (multicellular)

Fungi structure

Cytoplasmic membrane surrounded by a cell wall containing chitin & zymosan

Virus structure

Core of nucleic acid surrounded by protein coat (capsid), possibly with a lipid envelope surrounding capsid (larger viruses)

Virus infection mechanism

Virus protein/glycoprotein binds host cell surface receptors (Host cells with receptor for the virus are susceptible to infection)

Parasites

Invertebrates that require host to reproduce

2 groups of parasites

Protozoan (unicellular) & metazoan (multicellular - worms/helminths)

Examples of parasites

Protozoan - Toxoplasma gondii Metazoan- Dirofilaria immitis (heartworm)