Innate Immunity – Complement, Innate Immune Cell Activation and Antigen Presentation

Question 1

what are the two types of receptors on an innate immune cell?

Answer 1

1. phagocytic receptors - (scavenger receptors, mannose receptors)
2. Activation receptors- (toll like receptors)

Question 2

describe the process of antigen processing

Answer 2

1. During the process of phagocytosis proteins broken down to peptides
2. Peptides displayed on the surface
3. Present Peptides to T cells
4. Inform T cells what pathogen was detected

*Phagocyte = Antigen presenting cell*

Question 3

Know what APC, MHCClass2, Antigen and TCR refer to

Answer 3

Question 4

Describe the process of MHC Class 2 presentation

Answer 4

• Also known as Class II pathway
• Pathogens, toxins, fragments that have been ingested/phagocytosed
• Proteins digested to peptides in the phagolysosome
• MHC class II in the endosome and endosome fuses with phagolysosome
• Loaded onto MHC class II in the phagolysosome

Question 5

MHC peptide complexes are recognized by what kind of cell?

Answer 5

T cells

TCR recognises presented peptides, binds and becomes activated

Communicating about the pathogen to the adaptive immune arm

Question 6

What cells perform MHC Class 1 presentation?

Answer 6

all cells

Question 7

Describe the MHC class 1 presentation

Answer 7

• Also known as Class I pathway
• Cells infected by virus or intracellular bacteria
• Detected by host cells
• Virally produced proteins digested by proteasome
• Peptides transported into the endoplasmic reticulum
• Loaded onto MHC class I in ER

Question 8

What determines whether the antigen associates with MHC class 1 or 2?

Answer 8

–Depends on route by which antigen enters the cell

• Intracellular – infects target cell – any cell a target - MHC class I
• Extracellular – phagocytosed – only phagocytic cells involved – MHC class II

Question 9

Differentiate MHC Class 1 and MHC class 2

Answer 9

•MHC class I

found on all cells

• Presents material from intracellular organisms – viruses/bacteria/tumour proteins
• As all nucleated cells can be infected – MHC class I can be found all cells
• Upregulated during infection

•MHC class II

found on professional antigen presenting cells – macrophages, dendritic cells

• Presents material from phagocytosed bacteria/viruses
• Upregulated when APCs activated

Question 10

MHC class 1 and 2 are encoded by what genes?

Answer 10

they are encoded by HLA genes

Question 11

Describe the MHC diversity

Answer 11

the genes that encode for MHC class 1 and 2 are polygenic AND polymorphic

therefore, each individual has a unique set of MHCs with different ranges of peptide-binding specificites

They need different ranges of peptide recognition to fight all forms of infection

Question 12

What is responsible for marking your own cells as ‘self’?

Answer 12

MHC class 1 found on all cells - marks you own cells as ‘self’ therefore your immune system won’t attack them

Question 13

How do we prevent rejection of donor cells using our knowledge of MHC class 1 and 2 system ?

Answer 13

–T cells recognising non-self MHC

• Donor MHC class I cells not recognised by recipient cytotoxic T cells and killed immediately
• Donor Antigen presenting MHC Class II cells are attacked by recipient T helper cells and antibodies made
• Prevention – HLA typing- this way we can choose a donor most suitable
• Immunosuppressive drugs (T cells mainly)

Question 14

What were the results of the ‘sweaty T shirt experiment’

Answer 14

•Women preferred smell of men with different MHC molecules – pheromone driven

•

•MHC and olfaction – MHC can present pheromone peptides – peptides presented determines attraction

Question 15

If a pathogen breaches the epithelium, what works immediately?

Answer 15

Proteins in lymph/blood

• Complement
• Antibodies from previous encounters

then activation of innate immune cells - inflammation, phagocytosis, and antigen presentation

Question 16

what is the complement system?

Answer 16

a series of proteins
with high plasma concentration that fights infection
- innate immune mechanism- non specific

•

•Plasma contains 20+ proteins that circulate in the blood: complement (C) proteins:

–that ‘complement’ antibody action

–Complement proteins synthesised in liver

–Inactive proteins until activated by recognising bacteria/pathogen

–Cleaved by a protease to active form

–Majority once activated cleave and activate another part of the cascade

Question 17

What are C3a,b,and C5 responsible for immunologically?

Answer 17

C3a= inglammaotry response - proteins promote an inflammtory reponse - mast cells are degranulated causing increased vascular permeability - cause vasodilation, vascular permeability, chemoattraction and homing

C3b= opsonisation = C3b is left on the microbial cell wall (as opsonin) and is recognised by phagocytes who quickly eat the cell

C5= lysis = pops the cell by forming a multiprotein complex with C5-C9 and assembles on the surface of the pathogen to form a big whole. cell death occurs via loss of cell integrity

Question 18

what is the classical and alternative pathway for complement activation?

Answer 18

classical pathway = triggered by formation of the antibody antigen complex

Alternative pathway- where a component of complement binds to pathogen surface thus tagging it for destruction

Question 19

describe the general immune system response from the instant a pathogen enters …