Adaptive immunity

What are the functions of the lymphatic system?

• Returns interstitial fluid to circulation

• maintains pressure through drainage

• circulates immune cells

• exposes antigens to immune cells.

Name the main lymphoid tissues.

1. Tonsils

2. thymus

3. spleen

4. lymph nodes

What are lymph nodes and where are they located?

Bean-shaped, encapsulated nodes along lymphatic and large blood vessels in thorax and abdomen.

Describe the thymus.

Grows until puberty, then regresses but never fully disappears.

What does the spleen do?

• Filters aged RBCs and pathogens,

• contains lymphocytes

• structure varies across species.

How is lymph formed and what does it contain?

• Formed from blood contents exiting into interstitial space

• mostly water, salts, ~5% protein, WBCs, debris, pathogens, lipids.

What’s unique about lymphatic vessels?

One-way flow, high density in "dead-end" tissues to prevent backflow, drain into veins near heart, absent in CNS.

What are the types of naturally acquired immunity?

• Active: from infection

• Passive: maternal antibodies.

What are the types of artificially acquired immunity?

• Active: vaccination

• Passive: injection of immune serum.

What makes acquired immunity "specific"?

Targets specific antigens and retains memory for faster future responses.

Which cell produces antibodies?

Plasma cells (activated B cells).

What is humoral immunity based on?

Antibody activity by B cells.

What is cell-mediated immunity based on?

T cell activity.

Who produces cytokines?

All immune cells; also epithelial, endothelial cells, and adipocytes.

What % of WBCs are lymphocytes and what are their roles?

• ~30%; involved in antigen recognition

• antibody production

• cytotoxicity

• memory

• regulation

What is the function of the Bursa of Fabricius?

Site of B cell development in birds; required for antibody production.

Where do B cells originate and mature?

Originate in bone marrow; mature in lymphoid tissues like spleen and lymph nodes

What are the two types of B cells formed after activation?

Plasma cells and memory B cells.

What are the 6 steps of the humoral immune response?

1. Antigen recognition

2. B cell activation

3. Clonal selection

4. Antibody production

5. Antibody-antigen binding

6. Immunologic memory.

What can antibodies do to antigens?

Opsonize, neutralize, and form immune complexes.

What is the structure of an antibody?

• Y-shaped protein: 2 heavy chains

• 2 light chains.

• Constant region (same per isotype)

• variable region (antigen-specific).

What is IgG’s role?

Most abundant, protective against microbes/toxins, crosses placenta for newborn immunity.

Where is IgA found and what does it protect?

Secretions (saliva, milk, tears), mucosal surfaces.

What does IgE do?

Involved in allergic responses and defense against parasites.

What is IgM’s role?

First antibody produced in response; activates complement.

What does IgD do?

B cell receptor; involved in B cell activation.

What is required for T cells to recognize antigens?

Antigen must be presented with MHC proteins.

What do cytotoxic T cells do?

Kill virus-infected or cancerous cells by releasing toxins like perforin and granzymes.

What is the role of helper T cells?

Regulate immune responses by interacting with presented antigens.

What do regulatory T cells do?

Suppress B and T cell activity when response is no longer needed.

What do memory T cells do?

Remain in body to quickly respond to future antigen exposures.

Which cells initiate inflammation?

Mast cells and basophils (via histamine, prostaglandins).

Which cells are early responders to infection?

Neutrophils.

What do eosinophils do?

Phagocytose antigen-Ab complexes; involved in allergies.

What are macrophages' roles?

Phagocytosis and antigen presentation.