2.2

What are lymphoid organs responsible for?

Lymphocyte development, maturation, activation, and recirculation

What is lymphocyte recirculation?

The continuous movement of lymphocytes through blood, lymph, and lymphoid tissues

Where does hematopoiesis take place?

Bone marrow

What is hematopoiesis?

The production of blood cells

Where do B lymphocytes mature?

In the bone marrow

What occurs during B lymphocyte maturation?

Creation of a BCR that does not have affinity for self-antigen (host cells)

What does BCR stand for?

B cell receptor

What happens if B cells strongly recognize self-antigen?

They are eliminated or inactivated

Why is B cell selection important?

To prevent self-reactivity and autoimmunity

What do mature B cells do?

Bind antigen and produce antibodies

What are antibodies?

Proteins produced by B cells that bind specific antigens

What do immunological receptors have for antigens?

An “affinity”

What determines affinity?

Physical shape and chemical bonds present

What results from high-affinity binding?

Longer and more robust immune responses

What mediates immune complex formation?

Forces between antigens and antibodies/receptors

Why is B lymphocyte selection necessary?

To become mature B cells

What is an anergic B cell?

A B cell that becomes functionally inactive/unresponsive

What happens to self-reactive B cells?

They may become anergic or undergo apoptosis

Where do thymocytes mature?

In the thymus

What is a thymocyte?

An immature T cell

What types of cells are abundant in the thymus?

• T cells

• Dendritic cells/macrophages

• Epithelial cells

Which region of the thymus has more cells?

Cortex

Which region of the thymus has fewer cells?

 Medulla

What is the role of the thymus?

T cell maturation and selection

How are T cells presented antigen?

Via MHC molecules

What does MHC stand for?

Major Histocompatibility Complex

What does MHC Class I present antigen to?

CD8+ T cells

What does MHC Class II present antigen to?

CD4+ T cells

What kind of cells become CD8+ T cells?

Cytotoxic T cells

What kind of cells become CD4+ T cells?

Helper T cells

What is positive selection?

A thymic selection process ensuring TCR interaction with self-MHC

What does TCR stand for?

T cell receptor

Where does positive selection occur?

Between thymocytes and cortical epithelial cells expressing MHC

What is the purpose of positive selection?

• Ensures T cells recognize self-MHC

• Produces CD4+ or CD8+ cells

What happens to T cells that interact with self-MHC?

They are positively selected for and survive

What happens to T cells that cannot recognize self-MHC?

They die by neglect

What is negative selection?

Elimination of self-reactive T cells

Where does negative selection occur?

Between thymocytes and dendritic cells/medullary epithelial cells expressing self-antigen

What is the purpose of negative selection?

Prevents self-reactivity

What happens to T cells that strongly recognize self-antigen?

They are destroyed

Negative selection is similar to what other process?

B cell selection

What is thymic involution?

Shrinking of the thymus with age

What happens to thymic activity during involution?

T cell production decreases

What 2019 study/topic was referenced?

Reversal of epigenetic aging and immunosenescent trends in humans

What is immunosenescence?

Decline of immune function with age

What are lymph nodes?

Secondary lymphoid organs that filter lymph

What is the main function of lymph nodes?

Trap pathogens and activate immune cells

What fluid enters lymph nodes?

Lymph

What immune cells are commonly found in lymph nodes?

B cells, T cells, dendritic cells, and macrophages

What is the spleen?

A secondary lymphoid organ that filters blood

What is the main function of the spleen?

Removal of pathogens and old blood cells from blood

What type of circulation does the spleen monitor?

Blood circulation

What does MALT stand for?

Mucosa-associated lymphoid tissue

What is the role of MALT?

Protect mucosal surfaces from pathogens

What are Microfold (M) cells specialized in?

Endocytosis

What happens to pathogens encountered in MALT?

• Directly eliminated
  OR

• Transported to nearest lymph node for further processing

What does GALT stand for?

Gut-associated lymphoid tissue

Where are Peyer’s patches found?

Lining of the small intestines

Peyer’s patches are part of what?

GALT

What does BALT stand for?

Bronchus-associated lymphoid tissue

What does NALT stand for?

Nasal-associated lymphoid tissue

What does LALT stand for?

Larynx-associated lymphoid tissue

What does O-MALT stand for?

Organized mucosa-associated lymphatic tissue

What structures are part of O-MALT?

Tonsils (Waldeyer’s tonsillar ring)

What does CALT stand for?

Conjunctival-associated lymphoid tissue

What does SALT stand for?

Skin-associated lymphoid tissue

What does VALT stand for?

Vulvo-vaginal-associated lymphoid tissue

What does TALT stand for?

Testes-associated lymphoid tissue

What does D-MALT stand for?

Diffuse mucosa-associated lymphatic tissue

What is diffuse MALT?

MALT not organized as a separately identifiable mass, tissue, or organ

Difference between B cell maturation and T cell maturation?

B cells mature in bone marrow

T cells mature in thymus

Difference between positive and negative selection?

• Positive selection keeps cells that recognize self-MHC

• Negative selection destroys cells that strongly recognize self-antigen

Difference between MHC Class I and II?

• MHC I → CD8+ T cells

• MHC II → CD4+ T cells

Difference between cortex and medulla of thymus?

• Cortex has more cells

• Medulla has fewer cells