Lymphoid Organs & Lymphocytes

1. Thymus

2. Peyer's patches

3. Bone marrow

4. Bursa of fabricius (in birds)

What are the primary lymphoid organs?

1. Tonsils

2. Spleen

3. Lymph nodes

4. Peyer's patches

5. Bone marrow

What are the secondary lymphoid organs?

Primary lymphoid organs

Sites of lymphocyte development

Secondary lymphoid organs

Sites where lymphocytes respond to antigens

Produce mature, naive lymphocytes

What is the overall purpose of primary lymphoid organs?

V(D)J recombination

______________ produces an extensive repertoire of antigen recognition sites

B and T cell receptors

V(D)J recombination occurs where?

Bone marrow or thymus

What is the anatomic site of development immature lymphocytes and earlier precursors?

Thymus

Site of maturation of T lymphocytes

T cells, antigen presenting cells

In the thymus, the cortex contains __________ and the corticomedullary region/medulla contain _____________

T

T or F: Thymus regresses around puberty

Naive

Immunocompetent thymocytes are released into the blood as ____________ helper T or killer T cells

Thymus

Where does positive and negative selection occur?

Negative selection

Removes thymocytes that are capable of strongly binding with "self" MHC peptides

Autoimmune diseases

Negative selection prevents what?

Positive selection

Double positive T cells bind cortical epithelial cells expressing class I or class II MHC plus self peptides with weak antigen recognition, hence the ability to elicit an appropriate response

MHC-restricted non-self reactive

Positive selection causes cell proliferation of what kind of mature T cells?

1. Bone marrow

2. Bursa

3. Ileal Peyer's patches

What is the site of maturation of B lymphocytes in neonatal and adults?

Provide environment for antigen recognition by naive lymphocytes

What is the overall purpose of the secondary lymphoid organs?

Lymph nodes

This organ's structure ensures maximal proximity between lymphocytes and antigen presenting cells

B cells

What type of cells are in high concentration in the middle of a germinal center?

T cells

What type of cells are in high concentration in the marginal zone of the germinal center?

Spleen

Site of immune response to antigens in the blood

Red pulp

Part of spleen that filters blood and serves as a RBC storage area

White pulp

Part of spleen that the immune response occurs at

Mucosa associated lymphoid tissue (MALT)

Site of immune response to antigens along mucous membranes

Bronchus associated lymphoid tissue (BALT)

Lymphoid nodule associated with the respiratory tract

M cells

Specialized cells that transfer foreign antigens through the subendothelium to dome cells

Subepithelial dome

Lies underneath endothelium and contains dendritic cells which will go present antigens to lymphocytes in Peyer's patches

Cutaneous immune system

Process through which immune system responds to antigens penetrating stratified squamous epithelium

Langerhanns cells

What are the surveillance cells of the skin that present antigens?

Adhesion molecules and chemokines

Lymphocyte recirculation is governed by what?

High endothelial venule

Specialized post-capillary vascular epithelium present within lymph node paracortical region, point of entry for lymphocytes in blood into LN

Selectins and integrins

High endothelial venules have an upregulation of what?

Push lymphocytes out into the lymph node

What do selectins and integrins of the high endothelial venules do?

T cells

For most species what is the major lymphocyte?

CD4 (helper T cells)

For most species are CD4 or CD8 higher?

Bone marrow

Development of B cells occurs where?

Thymus

Development of T cells occurs where?

B and T lymphocytes

_______________________ are the only cells that recognize and respond specifically to antigens

Immunophenotype

Processes that identifies cells based on the types of antigens or markers on the surface of the cell

Secrete antibodies

What is the main function of B cells?

Secrete cytokines

What is the main function of helper T cells?

Kill abnormal cells

What is the main function of cytotoxic T cells?

Native

What type of antigen is recognized by B cells?

Processed peptide

What type of antigen is recognized by helper T cells?

Processed peptide

What type of antigen is recognized by cytotoxic T cells?

Helper T cells

CD4 is associated with what type of T cell?

Cytotoxic T cells

CD8 is associated with what type of T cell?

I

CD8 T cells bind to class _____ MHC molecules

II

CD4 T cells bind to class _____ MHC molecules

Cell mediated immunity

TH1 cells upregulate what?

Antibody production

TH2 cells upregulate what?

T

T or F: Receptor/ligand phenotypes can vary with lymphocyte maturation and activation status

F

T or F: Species will have the same receptor/ligand phenotypes on lymphocytes

Progenitor

A single _____________ cell gives rise to a large number of lymphocytes, each with different specificity

Tyrosine kinase phosphorylation

What is the key mechanism for lymphocyte cell activation?

Flow cytometry

What method is used to measure and classify lymphocytes?

Two dimensional plot

The pattern seen on a flow cytometer screen when analyzing lymphocyte populations stained with two different fluorescence conjugated antibodies; it is usual to label each population with a different colored dye

Histogram

Intensity of fluorescent labeling increases left to right with two distinct peaks (unlabeled and labeled) with the area under the peak being a measure of the size of each cell subpopulation

T

T or F: Flow cytometry is useful as a diagnostic tool