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Flashcards in Immune tissues Deck (16)
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Lymphoid tissues

Any tissue where clusters of lymphocytes can be found


Primary lymphoid tissues

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



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


T-cell differentiation

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


T-cell positive selection

The T-cells must bind to MHC-peptide complexes

This is facilitated by cortical thymic epithelial cells


T-cell negative selection

T-cells must ignore self antigens

This is facilitated by medullary thymic epithelial cells


Bone marrow

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


B-cell differentiation

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


B-cell positive selection

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


B-cell negative selection

The B-cells must ignore self antigen molecules


The lymphatic system

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


Secondary lymphoid tissues

The secondary lymphoid tissues are the site of immune response initiation

They include the spleen, lymph nodes and MALT


Lymph nodes

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



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


Mucosa-associated lymphoid tissue

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



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