Immune System, Microanatomy

Bean-shaped, encapsulated, highly organized structures.

Lymph nodes

There are about how many lymph nodes in the human body?

450 lymph nodes

Lymph nodes are grouped mainly in areas where lymphatics converge to form larger trunks:

1. Neck

2. Axilla

3. Groin

4. Lung hila

5. mesentery of the bowel

6. paraarotic areas

The lymph nodes process:

antigen from interstitial fluid that arrives at the node in the lymph

The functional components of the lymph node:

1. Cortex

2. Paracortex

3. Medulla

This portion of the lymph node is where B cell activation and clonal expansion to produce large numbers of B lymphocytes reactive to specific antigens. PRODUCTION OF MEMORY B LYMPHOCYTES.

Cortex of lymph node

This portion of the lymph node is where T cell activation and clonal expansion to produce large numbers of T lymphocytes, reactive to specific antigens. PRODUCTION OF T LYMPHOCYTES

Paracortex of lymph node

This portion of the lymph node is where plasma cell maturation and secretion of antibodies.

Medulla of lymph node

this lymph is where the effector T cells and plasma cells leave the nodes, then recirculate to the damaged or infected tissue.

Efferent lymph

This area of the lymph system is where water and electrolytes from the lymph that perculate through the node are returned to the blood circulation.

High endothelial venules

What are the three structural components of the lymph node?

1. Stromal compartment

2. Lymphatic/sinus compartment

3. Vascular compartment

This compartment of the lymph node is packed with lymphocytes and APCs

Stromal

this compartment of the lymph node acts as sieve for antigen.

lymphatic/sinus compartment

this compartment of the lymph node delivers lymphocytes to the lymph node along with the usual nutrients.

vascular compartment

this structure can be found throughout the medulla.

trabeculae

Plasma cells and their precursors:

plasmablast

What is the structure like of the medulla of the lymph node?

Branching medullary cords, separated by irregular medullary sinuses

(where B lymphocytes complete the final stages of maturation to form plasma cells)

Lymphoid tissue is distributed at many mucosal surfaces throughout the body, such as:

1. Gastrointestinal tract (GALT)

2. Bronchial tree (BALT)

3. Oropharynx (Waldeyer ring)

Mucosa-associated lymphoid tissue is arranged one of two ways:

1. Diffuse population

2. Non-encapsulated organized aggregations

What are some examples of non-encapsulated organized aggregations of mucosa-associated lymphoid tissue?

tonsils

Peyer’s patches

Deeply invaginates the tonsil, forming blind-ended:

tonsillar crypts

The base of the tonsil, separated from underlying muscle by a dense collagenous:

hemicapsule

The tonsillar parenchyma has:

numerous lymphoid follicles with germinal centers

The palatine tonsils form the waldeyer ring, along with:

lingual

pharyngeal

tubal tonsils (adenoids)

The luminal surface of the palatine tonsil is:

stratified squamous non-keratinized epithelium

These are a part of the GALT and the largest lymphoid aggregates:

Peyers patches

This antibody is the main one secreted in the gut of the lumen, protects against pathogens, and reaches the gut in the bile as well.

IgA

These antibodies are secreted into the lamina propria to protect the surface from organisms:

IgG and IgM

These antibodies triggers the release of histamine from mast cells (largely present in the lamina propria)

IgE

this acts as an integrated unit with a separate route of lymphocyte circulation in parallel with the peripheral lymphoid circulation.

MALT

This is the largest lymphoid organ

spleen

The spleen receives a rich blood supply via the:

splenic artery

The spleen is drained by the splenic artery into the:

portal vein

What is the function of red pulp of the spleen?

filter the blood to remove particulate matter

remove damaged and aged erythrocytes

recycling of iron to the BM

What is the function of the white pulp of the spleen?

mounts an adaptive immune response against blood borne infective agents

White pulp is also known as:

Malpighian corpuscles

Additional function of the spleen:

hematopoiesis in the normal fetus

in adults, certain diseases

Malignant tumors of the immune system:

leukemias

lymphomas

In transplantations, the immune system of the recipient reacts mainly against the MHC complexes,

Human leukocyte antigens (HLA)

this stain demonstrates the H. pylori organisms in the mucus layer at the surface of the epithelium

Cresyl violet

T cells are deficient due to thymic aplasia (absent), causing severe viral and fungal infections. The cell-mediated arm of the immune system is defective.

Di George syndrome

____ deficiency are more prone to infections of respiratory and GI tracts, like hypogammaglobulinemia and frequent bacterial infections.

IgA

X-linked agammaglobulinemia is also known as:

Bruton’s

Acquired immunodeficiency can be caused by:

drug-induced immunodeficiency

deliberate immunodeficiency for organ transplant recipients to avoid rejection

mild immunodeficiency

what occurs in primary immunodeficiency?

1. Both T and B lymphocytes are severely deficient

2. Patients subject to many infections

3. most severe forms are fetal in INFANCY

T cell types:

T helper cells

Cytotoxic T cells

Regulatory T cells

Memory T cells

Gamma delta T cells

Helper T cells will secrete this to help other cells perform their effector functions:

interleukins

Interleukins secreted by helper T cells provide help to:

B cells

Cytotoxic T cells

Macrophages

Helper T cells express surface markers, like:

CD2

CD3

CD4

Helper T cells are divided into subgroups:

TH1-cell mediated reaction

TH2-humoral (antibody mediated) response

TH17-Modify and augment certain types of acute inflammation

these T cells will kill virus-infected and some cancer cells.

Cytotoxic T cells

Cytotoxic T cells express surface markers, like:

CD2

CD3

CD8

Cytotoxic T cells require interaction with Th cells to become activated and proliferate, to form clones of:

effector cells

These T cells suppress immune responsiveness to self-antigens (autoimmunity) and will switch off reponse when antigen is removed.

Regulatory T cells

Regulatory T cells express surface markers, like:

CD4

CD25

FOXP3

These cells are developed from activated T cells, providing rapid reaction force for subsequent encounter with the same antigen (basis of vaccination)

Memory T cells

These T cells are a subset of T cells, a heterodimer. Populates the epithelium of the GI tract, CD8 positive

Gramma delta T cell

B cells are derived from precursors in the:

bone marrow

B cells synthesize large amounts of antibody (immunoglobulins), such as:

IgG

IgA

IgD

IgM

IgE

Immunoglobulin molecules are anchored in the:

plasma membrane of B cells

When the antigen-binding region binds to the antigen, the B cell will then become:

activated

B cells are involved in what kind of immunity?

Humoral immunity

IgM:

first antibody produced in primary immune response, activates complement

IgG:

Most prevalent antibody in the human body, primarily produced in secondary immune response and provides long term immunity

IgA:

Can be found in breast milk, tears, mucus, and saliva. Protects mucosa from infection from microorganisms

IgE:

Involved in type hypersensitivity reactions, parasitic infections, autoimmune processes and venom protection

IgD:

Role not completely understood

Immune response phases:

1. Recognition

2. Activation

3. Effector

This bone marrow produces all of the circulating and tissue resident blood cells, including the immature T and B lymphocytes. It is the site of B lymphocyte maturation.

Red bone marrow

The highly cellular cortex of the thymus functions as:

where T lymphocytes mature

The less cellular medulla of the thymus functions as:

develops the self-tolerance by deletion of self-reactive clones of T cells

the thymus produces various peptides with hormonal characteristics, such as:

thymulin

thymoproietin

thymosins

The thymus has several different cell types, including:

Epithelial cells (mechanical framework for lymphocyte population)

Cortical epithelial cells (promote T cell differentiation)

The epithelium of the thymus will form a sheath around blood vessels, creating a barrier to the entry of antigenic material into the thymus parenchyma, found in the cortex.

Blood-thymus barrier

The thymus is divided into two distinct zones:

1. basophilic outer cortex

2. inner eosinophilic medulla

These are immature and mature T cells, packed in the thymic cortex. Maturing cells will migrate from the cortex and into the medulla.

thymocytes

Lymphoma of the stomach (MALT) almost always have an infection with:

Helicobacter pylori

Where the effector T cells and plasma cells leave the nodes

Efferent lymph

Where water and electrolytes from the lymph that percolate through the node are returned to the blood circulation

high endothelial venules