Histology Third Parcial exam Immune system review material

approximately what fraction of circulating lymphocytes are T cells?

About 75% (course estimate).

how long does thymic selection take?

About two weeks 

what fraction of the spleen is white pulp?

20%

What percentage fail positive selection?

About 80% 

what percentage survive both selection stages?

2%

what proportion of immune cells is associated with MALT?

70%

Can routine light microscopy reliably distinguish B from T lymphocytes?

No; immunohistochemical markers are used.

a maternal example of passive immunity

Maternal antibodies transferred across the placenta to the fetus

How are Hassall corpuscles linked to Treg development?

They influence local dendritic cells through factors promoting regulatory T-cell development.

How are parental HLA alleles expressed?

Codominantly: alleles inherited from both parents are expressed.

How can stressed cells become NK targets despite having MHC I?

They express activating stress-associated ligands.

How do helper T cells coordinate immune responses?

They produce cytokines and provide cell-contact help.

How do thymocytes that fail selection die?

By apoptosis.

Closed Splenic Circulation

blood remains within endothelium-lined channels

Open Splenic Circulation

blood enters splenic stroma/cords

Open vs Closed Splenic Circulation

Blood remains in closed while blood enters in open

How does FDC antigen display differ from APC presentation to T cells?

FDCs display intact antigen to B cells; APCs present peptide-MHC complexes to T cells.

How does healthy-cell MHC I influence NK-cell killing?

It engages inhibitory receptors and helps prevent killing.

Describe the appendix's relationship to intestinal flora

It provides a “sample” of intestinal flora

How does thymic supporting stroma differ from that of lymph nodes and spleen?

The thymus has thymic epithelial cells, while the nodes and spleen have reticular-fiber networks.

How many different HLA molecules can a heterozygous person typically express per locus?

Two: one encoded by each parental allele.

How many lymph nodes are there in the body?

400-450

Name the three professional APC types listed.

Dendritic cells, macrophages, and B lymphocytes.

Name three cell types supported by helper T cells.

B lymphocytes, macrophages, and cytotoxic T cells.

Name three organized MALT examples.

Tonsils, Peyer patches, and the vermiform appendix.

early B-cell stages in order

Pro-B → pre-B → immature B → mature naive B.

Through which compartments do lymphocytes patrol?

Connective tissue, blood, and lymph.

What are the main functions of regulatory T cells?

Maintain self-tolerance and suppress excessive immune responses.

What are the spleen's two major pulp components?

White pulp and red pulp.

What cell type forms Hassall corpuscles?

Thymic epithelial cells.

What defensive role is emphasized for gamma-delta T cells?

Frontline defense at epithelial surfaces.

What do APCs display to conventional T cells?

Peptide fragments bound to MHC molecules.

What do M cells specialize in?

Capturing and transporting particles and microorganisms to underlying immune cells.

What does a CD4/CD8 double-positive thymocyte express?

Both CD4 and CD8.

What does a conventional TCR recognize?

A peptide together with its MHC molecule.

What does ADCC stand for?

Antibody-dependent cellular cytotoxicity.

What does CD stand for?

Cluster of differentiation

What does CD16 recognize during ADCC?

The Fc portion of antibodies coating a target cell.

What does HLA polymorphism mean?

Many different alleles exist in the population at an HLA locus.

What does HLA stand for?

Human leukocyte antigen.

What does MALT stand for?

Mucosa-associated lymphoid tissue.

What does MHC restriction mean for conventional alpha-beta T cells?

They recognize antigen in association with MHC molecules.

What does PALS stand for?

Periarteriolar lymphoid sheath.

What does positive selection preserve?

T cells able to recognize self-MHC appropriately.

What does SHM stand for?

Somatic hypermutation.

What fluid do lymph nodes filter?

Lymph

What fluid does the spleen filter?

Blood

What happens to an internalized antigen before MHC presentation?

It is broken down into peptide fragments.

What is a naive lymphocyte?

A lymphocyte that has not yet encountered its specific antigen.

What is active immunity?

The recipient develops their own immune response after infection or vaccination.

What is NK-cell “missing-self” recognition?

Reduced or absent MHC I removes an inhibitory signal and can favor killing.

What is passive immunity?

Protection from transferred antibodies rather than the recipient's own response.

What is the alternative name for CD40 ligand?

CD154 (CD40L).

What is the chance that two siblings inherit the same two parental HLA haplotypes?

25%

What is the goal of negative T-cell selection?

Eliminate strongly self-reactive T cells.

What is the leukocyte common antigen marker?

CD45.

What is the main effect of CTLs on a recognized target cell?

They induce apoptosis.

What is the origin of follicular dendritic cells?

Mesenchymal origin.

What is the role of high endothelial venules?

Entry of circulating lymphocytes from blood into lymph nodes.

What is the role of thymic macrophages?

Phagocytose thymocytes marked for elimination.

What is the usual source of MHC I peptides?

Proteins synthesized within the cell (intracellular/endogenous antigens).

What is the usual source of MHC II peptides?

Internalized extracellular material processed after endocytosis or phagocytosis.

What kind of immunity do B cells and plasma cells provide?

Humoral Immunity

What long-lasting cell populations are shown after vaccination?

Memory B cells and memory T cells.

What may be visible inside thymic macrophages?

Engulfed lymphocytes with pyknotic nuclei.

What MHC class is specifically mentioned for stellate thymic epithelial cells?

MHC ll

What presentation process occurs in lymph nodes?

Antigen presentation

What three B-cell outcomes are promoted by CD4 help in the figure?

Plasma-cell differentiation, affinity maturation, and class switching.

What tolerance process is a major thymic function?

Central tolerance, which helps prevent autoimmunity.

What two chains form MHC II?

One alpha chain and one beta chain.

What two components form MHC I?

An alpha chain with three domains and beta-2 microglobulin.

What two important B-cell outcomes follow antigen-dependent activation?

Memory B cells and antibody-secreting plasma cells.

What two organizational patterns can MALT have?

Diffuse scattered tissue or organized lymphoid aggregates.

What two threats do lymph nodes help prevent from disseminating?

Microorganisms and tumor cells.

When does thymic involution become prominent?

Around/After Puberty

Where are Hassall corpuscles found?

The thymic medulla.

Where are high endothelial venules located?

Paracortex.

Where are Peyer patches located?

Mucosa and submucosa of the ileum.

Where do activated dendritic cells migrate to initiate adaptive responses?

Lymph nodes

Where do B lymphocytes mature?

Bone marrow

Where do follicular dendritic cells display antigen to B cells?

Germinal centers

Where do many gamma-delta T cells reside?

In epidermal and mucosal epithelia.

Where do mature lymphocytes migrate to encounter antigen?

Secondary lymphoid organs

Where do T lymphocytes mature?

Thymus

Where does positive T-cell selection primarily occur?

Thymic cortex

Where is the thymus located, and how many lobes does it have?

in the mediastinum; has two lobes

Which adaptive branch is antibody-mediated?

Hummoral immunity

Which aging blood cells are removed by the spleen?

Old Red Blood Cells (erythrocytes)

Which cells are listed in lymph-node medullary cords?

B cells, plasma cells, and macrophages.

Which cells generally express MHC I?

All nucleated cells.

Which coreceptor characterizes cytotoxic T cells?

CD8

Which coreceptor characterizes helper T cells?

CD4

Which cortical epithelial cells form the cytoreticulum?

Stellate thymic epithelial cells.

Which cytokine identifies the Th17 lineage?

IL-17.

Which cytokine supports activated cytotoxic T-cell proliferation?

IL-2

Which cytokines are listed for Th1 differentiation?

IFN-gamma and IL-2.

Which cytokines are listed for Th2 differentiation?

IL-4 and IL-5.

Which death-receptor pathway is depicted for CTLs?

Fas ligand (FasL) binding Fas on the target cell.

Which differentiated B-cell descendants actively secrete antibodies?

Plasma cells

Which epithelial cells form the blood-thymus barrier in the slide?

Squamous thymic epithelial cells