Leukocyte Migration and Trafficking

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24 Questions

What is the primary purpose of leukocyte trafficking in the body?

To provide systemic protection through continual circulation

In which locations do lymphocytes constantly re-circulate?

Blood, spleen, and tertiary lymphoid tissues

How frequently can a complete circulation circuit of lymphocytes be performed in the body?

1-2 times per day

What is the function of secondary lymphoid organs such as lymph nodes?

Filtering of blood-born antigens

How do lymphocytes enter secondary lymphoid organs such as lymph nodes?

Via efferent lymphatic and blood vessels

What is the main purpose of the spleen in leukocyte trafficking?

To filter antigens coming from peripheral tissues

What must leukocytes do in order to transit the bloodstream?

Bind to endothelial cells lining the walls of blood vessels

Which factor significantly increases the chance of lymphocytes contacting antigens?

$1 in 105$ chance of contact

Where do lymphocytes enter through in the spleen to filter antigens coming from peripheral tissues?

Blood vessels

What ensures proper localization of lymphocytes in secondary lymphoid organs like lymph nodes?

Adhesion molecules and chemokines

How does immunity depend upon the continual circulation of leukocytes through the body?

To provide systemic protection

What happens when leukocytes bind to endothelial cells lining the walls of blood vessels?

They can transit the bloodstream

Which type of protein binds to selectins and other mucins on lymph node endothelium?

Mucins

What type of molecules are responsible for the initial contacts between leukocytes and endothelial cells?

Selectins

Which type of molecules bind to ICAMs along vascular endothelium?

Integrins

What controls chemotaxis, activation, and adhesion of leukocytes?

Chemokines

Where do naïve B and T cells circulate between according to different chemokine interactions?

Lymphoid tissues and lymphatics

What induces intracellular signals for pathogen killing and adaptive immune response alerting?

PRRs

Which immune cells migrate to sites of infection through blood and lymphatics?

Neutrophils

What ensures systemic protection by moving throughout the organism to find pathogens, reach lymphoid organs, and peripheral tissues?

Leukocyte trafficking

Where do effector lymphocytes exit via in order to reach inflamed tissues through blood?

Lymphatics

What possesses four conserved cysteine residues and controls chemotaxis, activation, and adhesion of leukocytes?

Chemokines

What do innate immune responses recognize in order to induce intracellular signals for pathogen killing and adaptive immune response alerting?

PAMPs

Which type of cells migrate to sites of infection through blood and lymphatics besides effector lymphocytes?

Granulocytes

Study Notes

  • Endothelial cells express 'cell adhesion molecules' (CAMs) such as selectins, integrins, and mucins.
  • Lymphocytes, granulocytes, and monocytes have receptors for these CAMs.
  • Leukocytes move towards chemokines according to their receptor expression patterns.
  • MUCINS: glycosylated proteins which bind to selectins and other mucins on lymph node endothelium.
  • SELECTINS: initial contacts between leukocytes and endothelial cells, bind specific carbohydrates (mucins).
  • INTEGRINS: heterodimers that bind to ICAMs along vascular endothelium.
  • CHEMOKINES: small peptides (90-130 Aa) controlling chemotaxis, activation, and adhesion of leukocytes, major regulators of leukocyte traffic, possess four conserved cysteine residues.
  • Lymphocytes circulate between secondary/tertiary lymphoid tissues and exit blood by extravasating at high-endothelial venules (HEVs).
  • Lymphocyte distribution: naïve B and T cells are guided by different chemokine interactions to distinct microenvironments.
  • Innate immune responses: recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs), induces intracellular signals for pathogen killing and adaptive immune response alerting.
  • Adaptive immune responses: effector lymphocytes exit via lymphatics and reach inflamed tissues through blood, expressing adhesion molecules and chemokine receptors, specific expression patterns regulate homing of effector lymphocytes.
  • Immune cell behavior in peripheral tissues: effector lymphocytes, neutrophils, and other immune cells migrate to sites of infection through blood and lymphatics.
  • Leukocyte trafficking: ensures systemic protection by moving throughout the organism to find pathogens and reach lymphoid organs and peripheral tissues.

Test your knowledge of leukocyte migration and trafficking processes, including the involvement of adhesion molecules, chemokines, and lymphocyte re-circulation in homeostatic and antigen entry conditions.

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