Exam 2 (Lecture 11) - Lymphocyte Circulation

Question 1

List two ways lymphocytes enter the lymphoid tissues from the bloodstream and compare the circulation of a naive lymphocyte and a memory lymphocyte.

Answer 1

1) Naive Lymphocyte
- wants to find its antigen
- will encounter antigen in lymphoid tissue dendritic cells
- gets into lymphoid tissues via HEVs (selectins and integrins)
- flow through lymph node and exits through efferent lymphatics (if it doesn’t encounter antigen)
- collect in the thoracic duct that goes into the cranial vena cava and into the bloodstream
- they repeat this process over and over until they encounter their antigen

2) Memory Lymphocyte
- effector cell needs to get to tissues where infection is
- exits bloodstream and goes out in the tissues
- if its antigen isn’t there it goes to the afferent lymphatics to lymph nodes
- exits through efferent to thoracic duct and into bloodstream
- can also exit through HEVs

Question 2

Describe high endothelial venules, function, surface molecules, and location.

Answer 2

Specialized blood vessels that support the migration of lymphocytes from the bloodstream into lymph nodes.

Normally found in secondary lymphoid organs (such as lymph nodes and Peyer’s patches).

Surface molecules: GlyCAM-1, ICAM-1, and CD34

Question 3

List the three professional antigen-presenting cells and give a brief explanation of how/when they present antigen.

Answer 3

APCs: present antigen on MHC I (because they are nucleated cells)
- Macrophages
- Dendritic cells (it can present to naive T cells); essential to activation of naive T cells
- Memory B cells

Question 4

Explain the difference between immature and mature dendritic cells.

Answer 4

Immature dendritic cell has to get the antigen to present (has to capture the antigen; lots of Fc receptors and C3b receptors to take antigen inside the cell).

Then, processes and presents on MHCII = mature dendritic cell.

Question 5

Explain what a Langerhans cell is, including where it is found.

Answer 5

Found in epidermis; collects antigens and then makes its way to lymphoid tissue and matures during this process.

Question 6

Describe how dendritic cells and follicular cells are different (ie origin, antigen presentation, and location).

Answer 6

1) Dendritic Cell:
- Originates in bone marrow
- Present antigen on MHC II
- Located in tissue (sentinel cells)

2) Follicular Dendritic Cell:
- Originates in the stroma/part of lymphoid tissue (NOT from pluripotent stem cells)
- Present antigen on the surface by trapping the antigen to give the B cell an opportunity to bump into it
- Located in follicles of lymphoid tissue (B cell area)

Question 7

List the three signals a naive T cell needs from the dendritic cell to respond.

Answer 7

1) Has to see peptide (MHC II); T cell receptor recognizes the peptide on MHC II
2) Cytokines
3) Co-stimulatory molecules (protection from autoimmune disease)

Question 8

Describe the difference in the humoral response for a T-independent B cell response and a T-dependent B cell response including the major differences in the antigens and the role the T cell plays in the different humoral response.

Answer 8

1) T-independent B cell:
- becomes plasma cell and produces IgM
- Ex: of T-independent antigen: lipids, CHOs, polysaccharides (when there’s no protein component, there’s no
T cell help

2) T-dependent B cell:
- T cell has to recognize a protein
- T cells help by secreting cytokines (then the cytokines initiate the isotype class switching, clonal expansion
and affinity maturation); you get IgG in the process

Question 9

Explain how the structure of the lymphoid tissue maximizes the opportunity for lymphocytes to meet antigen and interact with each other.

Answer 9

The structure of the lymphoid tissue is such that all of the lymphocytes are put into one area. This increases the chances of them meeting their antigen.