Cells & Tissues of Adaptive Immunity

Cells of the adaptive immune system all originate from…

common lymphoid precursor

Cells of the adaptive immunity

T & B cells

What is the unique characteristic of T & B cells?

Expression of antigen-specific receptors

B cell receptor (BCR)

A membrane bound Ig (antibody)

CD

Cluster of differentiation

Clusters of differentiation

Proteins or glycoproteins on surface of T & B cells that can act as markers for the specific cell type

How can we differentiate B & T cells in practice?

Stain for specific markers on each cell surface

Main marker for T cells

CD3 complex

Main markers for B cells

CD21, CD79 complex

Primary lymphoid tissues/organs

Organ of development of T & B cells

Key examples of primary lymphoid tissues/organs

-Thymus -Bone marrow -Bursa of fabricus -Ileal Peyer's patches

Key functions of primary lymphoid organs/tissues

-Develop lymphocytes from stem cell precursors -Generate diverse T & B cell receptors

Where do T cells develop?

Thymus

Where do B cells develop?

Bone marrow (most mammals) Bursa of Fabricus (birds) Ileal Peyer's patches (ruminants)

Maturation in primary lymphoid organs leads to…

expression of unique antigen-specific receptors by each T & B cell (generation of diversity)

What happens after T & B cells complete maturation?

Enter blood and recirculate between blood, secondary lymphoid tissues/organs, and lymph

Secondary lymphoid tissues/organs

Sites where T & B cells meet their specific antigens and immune responses occur - site of clonal selection and expansion

Secondary lymphoid tissue/organs are the site of initiation of…

adaptive immune response

Important secondary lymphoid tissues/organs

Lymph nodes Spleen Mucosa-associated lymphoid tissue (MALT) Tonsils

Difference between structure of lymph nodes and spleen and structure of MALT

Lymph node and spleen are encapsulated and MALT is not

Clonal selection

Antigen "selects" the T/B cells that have the correct antigen receptor and receptor binds, which activates expansion

Expansion

Following clonal selection, more of the particular T or B cells are created to respond to the pathogen

Lymph nodes are the site of clonal selection for antigens delivered from the ______

tissues

Spleen is the site of clonal selection for antigens delivered from the ______

blood

MALT IS the site of clonal selection for antigens delivered at the ______

mucosal sites

Thymus

Lobulated organ in cranial mediastinum

Thymus structure

Network of epithelial cells filled with macrophages and developing T cells

Cells in the cortex of the thymus

Cortical epithelial cells

Cells in the medulla of the thymus

Medullary epithelial cells

Bone-marrow derived cells in the thymus

Macrophages, dendritic cells, and T cell precursors

Functions of cortical and medullary epithelial cells

Help with development of T cells

___________ are sites where immune cells are present in high concentration

Lymph nodes

Where are B cells present in the lymph node?

Cortical area/lymphoid follicles

Where are macrophages present in the lymph node?

Medullary area

Where are T cells present in the lymph node?

T-cell area

Where are dendritic cells present in lymph nodes?

T-cell area and medullary area

Germinal centers

Location of B cell expansion in the lymph node

If a lymph node has germinal centers, it is always considered a…

secondary lymphoid tissue

Function of HEVs in lymph nodes

Entry point for lymphocytes into lymph node from the blood

What action takes place within the spleen due to immune response?

The spleen can enlarge (splenomegaly)

Types of MALTs

-Nasal associated lymphoid tissue (NALT) -Gut associated lymphoid tissue (GALT) -Bronchial associated lymphoid tissue (BALT)

Examples of NALTs

Tonsils and adenoids

Examples of GALTs

Peyer's patches, appendix

Site of immune transport across the gut lumen in the GALT

M cells