Lecture 1 - Immune System and Barriers to Infection

Innate Immune Response

Immune cells exhibit antimicrobial function immediately after infection, and in the same way during re-infection, every time

Adaptive Immune Response

Immune cells exhibit antimicrobial function after infection more slowly, but in a more protective, longer-lasting way

Pathogen

A microbe that causes disease in its host

Infection

When a microbe invades the body and multiplies

Disease

Tissue damage because of infection (clinical manifestations)

Pathogenesis

Molecular and cellular events that cause tissue damage and disease

What is the pathogenicity of a microbe defined by?

The microbe and immune resposne

Four major functions of the immune system

1. Prevent or limit infection

2. Identify/eliminate damaged cells

3. Prevent inadvertent damage to host

4. Prepare for future exposure to previous pathogen

Major Histocompatibility Complex I (MHC I) proteins

Helps our immune system recognize whether cells are “self”

• Every nucleated cell in our body expresses this

3 lines of defense against pathogens

1. Barriers

2. Innate Immune Response

3. Adaptive Immune Response

Physical barriers

Block pathogen from entering the body

• Skin, epiglottis, eyelids

Mechanical barriers

Actions that remove microbes and debris

• Shedding of skin cells, sneezing, coughing

Chemical factors

Proteins and other compounds produced by the body that inhibit or kill microbes

• Gastric juices, sebum

Normal microbiome

Microorganisms that are not pathogenic and are found all over the human body

How do normal microbiome compete with pathogens?

1. Compete for nutrients

2. Produce toxic substances

3. Stimulate host immune system

4. Take up space

What are the two main tissue systems with critical barrier function?

Skin & mucous membranes

How do most pathogens get into the body?

Mucous membranesP

Primary lymphoid tissues

Sites where immune cells are produced

• Thymus - T cells mature

• Bone marrow - T cells made here

Secondary lymphoid tissues

Sites where the adaptive immune cells are localized with antigens

• Spleen

• Lymph nodes

Where are all immune cells made?

Bone marrow

Where do T cells mature?

Thymus

Lymphatic system

Consists of specialized vessels that drain fluid from tissues

• Lymph nodes are interspersed along these vessels

Spleen

Initiates adaptive immune responses against pathogens that enter through the blood

Lymph nodes

Initiates adaptive immune responses against (most) pathogens that enter through skin or mucous membranes