Immune tissues

Question 1

Lymphoid tissues

Answer 1

Any tissue where clusters of lymphocytes can be found

Question 2

Primary lymphoid tissues

Answer 2

The site of immune cell development and education

In adults they include the thymus and bone marrow

In the foetus, the primary lymphoid tissue is the liver

Question 3

Thymus

Answer 3

The thymus is the site of education for T-cells

Thymocytes enter the thymus from the blood, before undergoing a complex differentiation process, moving from the cortex to the medulla as they do so

Thymic nurse cells facilitate T-cell development

Question 4

T-cell differentiation

Answer 4

1. Thymocytes enter the thymus at the corticomedullary junction
2. They then travel to the subcapsular cortex where they proliferate and begin to express the TCR
3. The cells then begin to express BOTH CD4 and CD8, before going through a round of positive and negative selection
4. The thymocytes are then mature and express EITHER CD4 or CD8

Question 5

T-cell positive selection

Answer 5

The T-cells must bind to MHC-peptide complexes

This is facilitated by cortical thymic epithelial cells

Question 6

T-cell negative selection

Answer 6

T-cells must ignore self antigens

This is facilitated by medullary thymic epithelial cells

Question 7

Bone marrow

Answer 7

The bone marrow is the site of development for blood cells and the site of the pool of haematopoietic stem cells

It is the site of education for B-cells

Question 8

B-cell differentiation

Answer 8

Less well understood, assumed to follow the some method as T-cell development

B-cells must pass a round of positive and negative selection before they are released into the blood

Question 9

B-cell positive selection

Answer 9

The B-cells must bind to and respond to survival factors

Question 10

B-cell negative selection

Answer 10

The B-cells must ignore self antigen molecules

Question 11

The lymphatic system

Answer 11

The lymphatic system is a transport system for leukocytes

Movement occurs via adhesion molecules, smooth muscle movement, residual arterial pressure and back-flow prevention valves

Question 12

Secondary lymphoid tissues

Answer 12

The secondary lymphoid tissues are the site of immune response initiation

They include the spleen, lymph nodes and MALT

Question 13

Lymph nodes

Answer 13

Found throughout the body

Have a cortex (containing mostly B-cells) and a paracortical area (containing mostly T-cells)

Facilitates encounters between antigens and lymphocytes

Question 14

Spleen

Answer 14

Filters the blood directly

Has immunological and non-immunological roles

The red pulp filters old and damaged erythrocytes

The white pulp facilitates encounters between antigens and lymphocytes

Question 15

Mucosa-associated lymphoid tissue

Answer 15

MALT describes zones containing high concentrations of T-cells and B-cells in mucosal membranes

Question 16

GALT

Answer 16

Gut-associated lymphoid tissue is found in the intestinal epithelium and includes Peyer’s patches

It is seen as aggregates of lymphoid cells

M-cells transport suspected antigen across the epithelium towards these aggregates