Cell Adhesion

Question 1

Cell adhesion is manifested in (5)

Answer 1

• immune response in inflammation
• formation of blood clots
• cell proliferation (growing + dividing)
• artificial tissue assembly
• polymeric device implant

Question 2

Immune response examples

Answer 2

1. important role in leukocyte extravasion»>
   movmement of leukocytes out of the circulatory system and towards the site of tissue damage/infection
2. adhesion between cyto-toxic T cell and target cell

Question 3

Name & briefly describe experimental ways to measure cell adhesion

Answer 3

1. 2 micropipettes (mp) - measuring conjugation & separation of a cytotoxic T cell & target cell, 1 rigid mp 2 flexible mp
2. Microscope - study deformation of cell adhered on the flat substrate under flow
3. Flexible micropipette - use displacement transducer to pull cell away from substrate & use position sensor to measure how much force is generated between substrate + cell
4. Long focal microscopy systems - poor resolution

Question 4

AFM Microscopy description

Answer 4

1. microbead attached to flexible cantilever beam
2. cell on top of substrate
3. lower cantilever beam to make contact with cell and indent cell to measure
4. instead of microbead could use another cell to measure the cell adhesion
5. once cells/microbead in contact, reverse direction of the cantilever

Question 5

Which type of cell has a higher elastic modulus than healthy cell

Answer 5

Diseased cell - cytoskeleton distribution is distorted and not uniform, preferential alignment occuring

Question 6

Ligand-receptor binding for cell adhesion

Answer 6

1. Binding of a chemical species with another which has complementary structure
2. come in closely matched pairs
3. binding of a ligand receptor changes its shape/activity allowing it to transmit a signal or directly produce a change inside a cell

Question 7

What was found when measuring the breakage of molecular binding between cells measured by AFM

Answer 7

smaller distance required to separate 2 diseased cells

Question 8

What are the two phases of cell adhesion?

Answer 8

1. Contact

2. Separation

Question 9

Describe the contact phase for healthy cells

Answer 9

• cytoskeleton uniformly distributed in cells

- more molecule binding on the surface

Question 10

Describe the contact phase for diseased cells

Answer 10

• preferentially aligned cytoskeleton

- less molecule binding on surface

Question 11

What 2 things occur when pulling speed is increased?

Answer 11

• maximum unbinding force increased

- more energy required to separate cells

Question 12

Optical tweezers for cell adhesion

Answer 12

• force output slightly lower than AFM

- combined with mp adhesion to measure adhesive strength of receptor-ligand bonds

Question 13

What is an example of specific interaction in cell adhesion?

Answer 13

Ligand-receptor interaction

Question 14

What is an example of non-specific interaction in cell adhesion?

Answer 14

1. Van der waals attraction
2. Double-layer repulsion
3. Thermal membrane fluctuation