Week 2: Innate Immunity versus Adaptive Immunity

Question 1

Function of the Immune System

Answer 1

Main function is to protect body from pathogens that can make you sick

Destroy abnormal cells (cancerous)

Question 2

Immune System Has two systems in order to protect against pathogens:

Answer 2

1. Innate immune system (made up of barriers and innate cells)
2. Adaptive immune system (B Lymphocytes and T Lymphocytes)

Antigens are foreign substances recognized by the immune system.
They can be infectious agents like viruses or non-infectious substances.
Examples include bee venom or drugs.

Immune response is activated when antigens are recognized.

The immune system has innate and adaptive systems.
Innate: barriers and white blood cells.
Adaptive: B and T lymphocytes.
B cells activate the humoral immune system.
T cells activate the cell-mediated immune system.

Question 3

Properties of Innate Immune System

Answer 3

INNATE = present since birth
No memory (non-adaptive)

Immediate response

Non-specific

Uses Pattern Recognition Receptors (PRRs)

Has first and second lines of defense

Recognizes self from nonself

Prevents infection and deeper tissue penetration

Responds to any pathogen

First line: physical barriers, secretions
Second line: white blood cells, complement system

Question 4

Portals of Entry (pathogens)

Answer 4

skin
GI tract
respiratory tract
urogenital

Question 5

GI Tract Portal of Entry

Answer 5

• gastrointestinal tract: can swallow gastric secretions into the respiratory tract = aspiration pneumonia
• the gastrointestinal tract is generally decal oral contamination, so something that has been on the hands then our hands touch our face and get into the GI tract (bacteria through foods too

Question 6

Urogenital Tract portal of entry

Answer 6

• urogenital tract – the pathogens cause infection by either local invasion of the skin or mucus membranes – this is usually through sexual contact or by ascending infections where organisms can ascend through the urethra to infect the bladder or renal pelvis

Question 7

Physical Barriers

Answer 7

• Skin (tight junctions of epithelial cells) – largest barrier
• Mucous Membranes (globlet cells produce mucous, ciliated epithelial cells sweep it away)

Question 8

Chemical Barriers

Answer 8

• Acidic environments
• Lysozyme
• Microflora – GI system

Question 9

Microflora associate with epithelial cells that line all pathogen entry points:

Answer 9

GI: coliforms, enterococcus spp, anaerobic bacteria

Genital Tract: Lactobacillus spp, candida in women

Mouth/Upper Resp: strep, Haemophilus, Neisseria, actinomyces, trichomonads, anaerobic bacteria

Skin: Staph, strep, pityrosporum, anaerobic bacteria

Question 10

Leukocytes

Answer 10

are white blood cells include neutrophils, monocytes, macrophages, eosinophils, basophils

Question 11

Dendritic cells

Answer 11

are bone marrow-derived leukocytes, and mast cells are another type of white blood cell found in connective tissues

Question 12

Natural killer cells

Answer 12

are white blood cells called lymphocytes they have a role in the innate immune system, as well as the adaptive immune system as well,

remember, the B cell and T cells are also lymphocytes…

Question 13

Neutrophils

Answer 13

• First responders
• Live in blood

are the early responding cells of the innate system, and are the predominant white cells in the blood.

Question 14

Macrophage

Answer 14

• Arise from blood monocytes
• Can consume larger particles

arise from blood monocytes, and they participate in phagocytosis of larger particles that neutrophils may be unable to handle.

Question 15

Immature dendritic cells

Answer 15

An important intermediary between the innate and adaptive immune system

• Dendritic cells are important intermediary cell between the innate and adaptive immune system. An immature dendritic cell is able to be involved in phagocytosis, whereas a mature dendritic cell helps to initiate the adaptive immunity response. So the DC role & function depends on maturation state

Question 16

Defensive cells

Answer 16

are white blood cells called phagocytes that “eat” unwanted invaders of the body, as well as dead or damaged cells.

Question 17

Phagocytes

Answer 17

• Phagocytes are nonspecific and will get rid of pathogenic organisms, as well as dead or damaged cells or unwanted debris found in the body
• Function: To kill extracellular pathogens by phagocytosis

Question 18

Recognition and adherence:

Answer 18

Neutrophils and macrophages have PRRs (like Toll receptors) that bind to PAMPs on microbes.

Phagocytosis is triggered:
Pathogen binds to phagocyte.
Phagocyte engulfs pathogen, forming a phagosome.
Phagosome fuses with lysosome (phagolysosome), containing antimicrobial molecules and enzymes.
Microbe is killed and digested.

Result: kills pathogen!

Question 19

Eosinophils

Answer 19

• Defense against parasitic infections
  o Able to digest much larger particles
• Also have role in allergic reactions
• Eosinophils are another type of leukocytes. Their main role is defense against parasitic infections, as their able to digest much larger particles, and they also have a role in allergic reactions

Question 20

Lymphocyte – Natural Killer

Answer 20

Natural Killer (NK) cells:
Constantly monitor body for abnormal cells.

Kill intracellular viruses and some cancer cells.

Contain cytoplasmic granules with toxic enzymes.

Inject enzymes into abnormal cells, inducing apoptosis.

Viruses need host cells for reproduction.

NK cells identify and destroy infected and tumor cells.

They distinguish normal from abnormal cells via receptors.

Normal cells express MHC-1, inhibiting NK cell activation.
Infected cells lack MHC-1, activating NK cell to destroy them.

Question 21

Defence Proteins

Answer 21

Complement system - 30 or more plasma and cell surface proteins that work in concert to fight invading microorganisms through
o Opsonization → phagocytosis
o Inflammation
o Lysis

• The complement system is so named because it is complementary to the antibody response of the adaptive immune system

Question 22

Cytokines→→→→Pro-Inflammatory response

Answer 22

Main types of Cytokines:
- Chemokines
- Interferons (IFN)
- Interleukins (IL)
- Tumor Necrosis Factor (TNF)

Cytokines are key in innate immunity.

They form an integrated signaling network.

Roles include inflammation and immune response.

Proinflammatory cytokines: Chemokines and interferons.

Chemokines attract leukocytes via chemotaxis.

Interferons combat viral infections.

Question 23

Properties of Adaptive Immunity

Answer 23

Adaptive Immunity:
Distinguishes specific microbes.
Develops memory for faster response.

Two types: Humoral and Cell-mediated.
Humoral Immunity:
Involves antibodies from B cells.
Antibodies produced by plasma cells.

Cell-mediated Immunity:
Destroys invading microorganisms.
Aids B cells in antibody production.

T-cell immunity:
Important against intracellular pathogens.

B cell immunity:
Eliminates extracellular pathogens.

Can’t differentiate self from microbial antigens (→ autoimmune disorders).

Question 24

Humoral Immunity

Answer 24

B Cell Function:
Produces antibodies against extracellular pathogens.

Origin:
Arise in fetal liver and bone marrow.
Mature in bone marrow, enter circulation, stored in lymphoid tissues (spleen, lymph nodes).

BCR:
B Cell Receptor = Immunoglobulin molecule.
Antibodies:
Also known as Immune Globulin (Ig).

Acronym “GAMED”

Question 25

Role of Antibodies

Answer 25

Help eliminate extracellular pathogens via

1. Neutralization – block pathogen receptors that are used to gain entry into a cells or tissues
2. Phagocytes express surface receptors that bind Antibodies, called Fc receptors, which triggers phagocytosis.

Question 26

IgM

Answer 26

“It’s Got Me” – acute infection

Prominent in the primary antibody response. Main function is to neutralize pathogens

Question 27

IgA

Answer 27

Found in bodily secretions such as tears, saliva, intestinal mucus, milk, prostatic fluid, and other secretions. Therefore, its main function is mucosal immunity on surfaces of the GI and respiratory tract that protect against the entrance of bacteria. It also therefore provides passive immunity to a newborn breast feeding as maternal IgA is the most predominant Ab in colostrum and breast milk.

Question 28

IgG

Answer 28

The most abundant antibody – its most important feature is that it is able to cross the placenta and protect the fetus resulting in PASSIVE immunity for the fetus that generally lasts for 3 months after birth. It is prominent in the secondary immune response. Its main function is to enter infected tissue via inflammation to neutralize pathogens and enhance phagocytosis.

Question 29

IgE

Answer 29

Participates in immediate hypersensitivity a type of allergic reaction in which a specific allergen, as well as some parasitic infections as it activates mast cells. Does not function in neutralization of phagocytosis.

Question 30

IgD

Answer 30

Mostly remain bound to naïve B cells – main function is to act as a B cell receptor (bind antigens. It’s Ab function is unknown

Question 31

Cell-Mediated Immunity

Answer 31

Deals with INTRAcellular bacteria, viruses, and any bacteria that are out of the reach of antibodies and have escaped phagocytosis

T Cells arise in the bone marrow  migrate to the Thymus to undergo several steps of maturation

TCR (t cell receptors) , CD4 and CD8 co-receptors

Helper T cells and Cytotoxic T cells

Question 32

Main Defenses in T cell Immunity

Answer 32

• T Helper Cell (CD4+)
• Cytotoxic T Cells (CD8+)