Innate & Acquired Immunity

What is innate immunity?

Non specific and the bodies first line of defence against foreign bodies.

Why is innate immunity referred to as non-specific?

As it is able to protect the body against foreign cells or substances without having to recognise their specific identity.

Does innate immunity require previous exposure to a pathogen or its products?

No as it is able to recognise a general, conserved property that mams the invader as forgein.

Is this a learnt or inherited ability?

Inherited

Body surfaces function in innate immunity?

Initial line of defence against microorganisms as they can’t penetrate intact body surfaces.

What are skin glands able to do?

Secrete anti-microbial molecules such as mild acids and enzymes.

What does mucus do for immunity?

Due to its sticky nature it can trap invaders and it is also microbial.

Name two more ways that the body can innately protect itself from foreign bodies

• Stomach acid

• tear fluid, sweat and urine flushes out

What are phagocytes?

cells capable of phagocytosis

What is phagocytosis?

A type of endocytosis in which a cell engulfs particulate matter and destroys it via proteases and oxidising compounds.

Where are phagocytes found?

Within body fluids and within various tissues & organs.

What are the most common phagocytes in vertebrates?

A type of blood cell called leukocytes

Where are leukocytes derived from?

Hematopoietic stem cells in bone marrow

Name the 6 main types of leukocytes

1. neutrophiles

2. eosinophils

3. monocytes

4. macrophages

5. basophils

6. natural killer cells

Are there any more types of cells involved in innate immunity?

Yes, dendritic cells and mast cells are derived from bone marrow.

Name the subtypes of innate immune cells

Granulocytes and monocytes

Describe neutrophiles

• Phagocytise and kill bacteria.

• Mediate inflammation.

• Normally first cell to arrive

Describe eoisinphils

• Release chemicals that kill parasites.

• Phagocytise certain parasites.

• Participate in allergic responses.

Describe monocytes

Develop into macrophages

Describe macrophages

• Phagocytize microbes

• mediate inflammation

• present antigens to adaptive immune cells (T cells)

Describe basophils

Enter tissues at the site of injury and secrete heparin (anti-clotting factor) and histamine

Describe natural killer cells

Attack generous features in cancerous cells and virus infected cells

also part of adaptive immunity.

What are dendritic cells

• Properties like macrophages

• main antigen presenting cell

Give examples of leukocytes that are classified as granulocytes

• Neutrophil

• basophil

• eusophil

Give examples of leukocytes that are classified as monocytes

• monocyte

• macrophage

Describe mast cells

• Secrete histamine in inflammatory responce

• participate in allergic reactions

What is inflammation

An innate local response to infection of injury.

What are the functions of inflammation

Allows the elimination of foreign invaders, clears area of dead cells and sets stage for tissue repair

Destroys and inactivates pathogens.

What are the key cells involved in inflammation

• neutrophils

• macrophages

• dendritic cells

• mast cells

How is inflammation induced and regulated

Chemical mediators including a family of proteins called cytokines

Where are cytokines secreted

• immune cells

• fibroblasts

• endothelial cells of blood vessels

Step 1 of inflammation

1. An injury such as a splinter introduces bacteria under the skin.

2. inflammatory signals produced by injured tissue:

mast cells secrete histamine

neutrophils and endothelial cells secrete nitric oxide to induce vascular change

Step 2 inflammation

3. Capillaries dilate and become leaky

• increased blood flow to area increases delivery of beneficial proteins and leukocytes

• increased vascular permeability allows plasma proteins to enter interstitial fluid.

4. Fluid and neutrophils exit the capillaries and enter the site of the wound.

Step 3 inflammation

5. Once phagocytes enter the area and encounter microbes, they release inflammatory mediators (e.g. cytokines) that bring even more phagocytes.

6. Neutrophils and macrophages engulf and destroy bacteria.

7. Capillaries return to normal, and infection is brought under control.

8. Imperfect tissue repair = scar tissue

What does PAMP stand for

Pathogen- associated molecular patterns (PAMPs)

What does innate immunity depend on?

The recognition of features common to many types of pathogens. (PAMPs)

How is recognition accomplished in innate immunity

Recognition is accomplished by toll like receptors on membranes of immune cells e.g. macrophages and dendritic cells.

Role of TPs in innate immunity

TPs recognise and bind to pathogens with PAMPs.

E.g. microbial lipids and carbohydrates such as lipopolysaccharide (LPS), Viral and bacterial nucleic acids pr bacterial flagellum.

What are PAMPs

• PAMPs are conserved molecular features that are vital to the survival of the pathogen.

• a PAMP on a pathogen binding to a TLR on an immune cell will lead to immune cell activation.

What is adaptive immunity

• Requires exposure to foreign substances known as antigens.

• specific

what is an antigen

any molecule that the host doesn’t recognise as itslef

What are the 2 types of acquired immunity

1. cell mediated immunity

2. humoral immunity

what is humoral immunity

where plasma cells secrete antibodies that bind to antigens

What is cell mediated immunity

Cytotoxic T cells directly encounter and destroy infected, cancerous and transplanted cells

Name and describe the type of cells involved in the adaptive immune response

Type of leukocyte called lymphotypes:

1. Helper CD4 T cells

• CD4 T cells assist in activating cells

2. Cytotoxic CD8 T cells

• CD8 T cells directly kill infected cells

(cells involved in cell mediated immunity)

3. B cell

4. plasma cell

• secrete antibodies

(cells involved in humoral immunity)

5. NK cells

• similar to T cells but also perform non-specific actions

where can lymphocytes be found

• in blood

• mainly in groups of organs/tissues that constitute the lymphatic system

what is the lymphatic system composed of

Lymphatic system is a network of lymphatic vessels and lymphoid organs with circulating lymphocytes

Name the 2 groups of organs in the lymphatic system

1. primary lymphatic organs

2. secondary lymphatic organs

Role of primary lymphatic organs

Where B and T cells mature

• B cells = bone marrow

• T cells = thymus

role of secondary lymphatic organs

Where lymphocytes activate and replicate

Where do lymphocytes circulate

Lymphocytes circulate in blood, but most reside in the lymphatic organs

Why do lymphocytes circulate

Circulating the lymph increases the chance that they will encounter their antigen

Describe T cells and cell mediated immunity

• T cell receptors for antigens have specific regions that differ from one T cell clone to another.

• receptors remain embedded into the plasma membrane and are not secreted like antibodies

• cannot combine with antigen unless complexed on major histocompatibility complex molecule (MHC)

What is the major histocompatibility complex (MHC)

• MHC are cellular identify tags and are genetic markers of self.

Name 2 types of MHC

1. MHCII Class II

2. MHC Class I

Where is MHCII class II found

MCHII class II is found only on antigen presenting cells (APCs) such as macrophages, B cells, and dendritic cells (DCs).

• CD4 on helper T cells binds to MHC class II

Where is MHC class I found

MHC class I is found on all cells in the body except erythrocytes

• CD8 on cytotoxic T cells binds to MHC class I

Step 1 of antigen presenting cells presenting antigens to CD4 helper T cells.

Microbe (e.g. bacteria) is phagocytized by macrophages or DC and digested into fragments or epitopes.

Step 2 of antigen presenting cells presenting antigens to CD4 helper T cells.

Fragment -MHC complex is transported to cell surface.

Step 3 of antigen presenting cells presenting antigens to CD4 helper T cells.

• specific helper T cell binds to complex with CD4 protein helping link

• this is essential to helper T cell activation, but co-stimulatory molecules are also required.

• APC also secretes cytokines -IL-1 and TNF to stimulate attached helper T cell.

What is the role of an activated helper T cell in adaptive immunity

Activated helper T cells can stimulate cytotoxic T cells to proliferate.

• helper T cell binds to macrophages that has phagocytized the same type of virus

• helper T cell then proliferates and binds to cytotoxic T cells.

• The helper T cell can also secrete IL-2 and other cytokines that stimulate other helper T cells and cytotoxic T cells to divide.

What is the role of cytotoxic T cells

• cytotoxic T cells bind to virus infected cells.

• cytotoxic T cells secrete proteases and perforin, which inserts into the plasma membrane of the virus infected cell to form channels. The cell takes up water and proteases and bursts.

What activated B cells in humoral immunity

Activated by a antigens and helper T cells

What do B cells proliferate into in humoral immunity

Proliferate into plasma cells that make antibodies

Role of B cells in humoral immunity

Major defence against bacteria, viruses, and other microbes in the extracellular fluid, and against toxins.

What are the antibody immunoglobulin (Ig) protein family composed of

each composed of:

• two heavy chains

• two light chains

Describe the regions in the immunoglobulin protein family

• variable region - varies among different B cells, and this is what specifically recognises antigen.

• constant region - is a Fc domain identical for given class

Name the 5 classes of immunoglobulins found in mammals

IgM, IgG, IgE, IgA, IgD

Step 1 of activated B cells and humoral immunity

• Antigen binds to a B cell displaying a specific immunoglobulin.

• binding of antigen stimulates only this specific B cell to divide.

  this is clonal selection

Step 2 of activated B cells and humoral immunity

• Multiple cell divisions result in a clone of this specific type of B cells.

• progeny of this lymphocyte/ B cell all express the same receptor.

Step 3 of activated B cells and humoral immunity

Cloned B cells differentiate into plasma cells, which secrete antibodies; recognising the original antigen.

These antibodies can inactivate the pathogen.

How can antibodies made by plasma cells inactivate pathogens

• Opsonisation - antibody marks pathogen for phagocytosis by immune cell.

• forms complexes destroyed by phagocytes

• block binding sites so viruses cannot invade.

What happens when an antigen binds to a B cell displaying a specific immunoglobulin

Clonal selection: Stimulates only this specific B cell to divide.

What do cloned B cells differentiate into in humoral immunity

plasma cells, which secrete antibodies that recognise the original antigen.

How is excessive immune response prevented

• Effector plasma cells and cytotoxic cells die by apoptosis to prevent excessive immune response.

• Some T and B cells persist as memory cells, awaiting future infection by the same pathogen.

What is the role of natural killer cells (part innate, part adaptive immunity)

• can also destroy virus infected and cancerous cells by secreting toxic chemicals

• recognises general features of virus infected or cancerous cells as part of non-specific immunity.

• Can be linked to target cells by antibodies

Are both, innate and adaptive immune responses interlinked

yes

Give an example of innate and adaptive immunity being interlinked

Upon influenza viral infection in the lung

• innate immune cells = MCHII+ = macrophages and dendritic cells

• adaptive immune cells = B cells and T cells