MELS502 Week 1 - Immune System

Immunology

ranch of biology that studies the immune system and immunity?

Main features of immune system

Innate immune system, adaptive immune system, organs and tissues, communication, immunological memory, self vs non-self recognition

Which arm of immunity possesses immunological memory?

Adaptive immunity

What are the primary lymphoid organs where lymphocytes mature?

Bone marrow and thymus

List four secondary lymphoid organs.

Lymph nodes, spleen, tonsils, mucosa-associated lymphoid tissue (e.g., Peyer’s patches)

What fluid, similar to plasma but lower in protein, circulates in lymphatic vessels?

Lymph

Approximately how many litres of tissue fluid are returned to the blood daily via the lymphatic system?

About 3 L per day

Which vessels drain excess interstitial fluid and return it to venous blood?

Lymphatic vessels

Into which larger duct does lymph from the right upper quadrant of the body drain?

Right lymphatic duct

Where does lymph from the rest of the body ultimately empty?

Thoracic duct

What is the major haematopoietic tissue producing all formed blood elements?

Red bone marrow

Which type of bone marrow is inactive and rich in fat?

Yellow bone marrow

Where in bones is marrow located?

In the medullary (hollow) cavities

Which primary lymphoid organ is bilobed and sits anterior to the heart?

The thymus

What are the two main histological regions of a thymic lobule?

Cortex and medulla

In which thymic region does negative selection of self-reactive T cells mainly occur?

The medulla

Hormones secreted by the thymus to promote T-cell maturation

Thymosin, thymopoietin, thymulin

Through which vessels does lymph enter a lymph node?

Afferent lymphatic vessels

What lymph-filled space lies directly beneath the lymph-node capsule?

Subcapsular sinus

Where are B-cell follicles located in a lymph node?

In the outer cortex

What lighter-staining area forms inside a secondary follicle following antigenic stimulation?

Germinal centre

Which zone of a lymph node is rich in T cells?

Paracortical (deep cortical) area

Clinically important superficial lymph-node groups routinely palpated

Cervical, axillary, inguinal, epitrochlear, iliac/para-aortic nodes

Largest secondary lymphoid organ in the body?

The spleen

What splenic region destroys aged red blood cells?

Red pulp

What structure surrounds arterioles and is rich in T cells within the spleen?

Periarteriolar lymphoid sheath (PALS) in white pulp

Defensive functions of the spleen

Phagocytic removal of microbes/old RBCs; immune activation against blood-borne antigens; tissue repair; blood reservoir)

Which lymphoid tissues form the pharyngeal lymphoid ring?

Pharyngeal (adenoid), palatine (pair), lingual, and tubal (pair) tonsils

What percentage of whole blood volume is plasma?

About 55 %

Which plasma protein is most abundant and helps maintain osmotic pressure?

Albumin

Name the three major categories of formed elements in blood.

Erythrocytes, leukocytes, and platelets

Define haematopoiesis.

The formation and development of mature blood cells from multipotent haematopoietic stem cells

Where does adult haematopoiesis primarily occur?

Red bone marrow

Which two broad progenitor lineages arise from pluripotent haematopoietic stem cells?

Common myeloid progenitor and common lymphoid progenitor

Give three cell types derived from the myeloid lineage.

Erythrocytes, platelets, neutrophils, eosinophils, basophils, monocytes, dendritic cells, mast cells (any three)

Which cytokine is critical for lymphocyte development, especially B and T cells?

Interleukin-7 (IL-7)

How are leukocytes classified based on granules and nuclei?

Granular vs. agranular; polymorphonuclear vs. mononuclear

Which white blood cell type normally accounts for 60–70 % of circulating leukocytes?

Neutrophils

What term describes an elevated white blood cell count?

Leukocytosis

Give two possible causes of leukopenia.

Bone-marrow disorders, severe infection, autoimmune disease, chemotherapy, etc.

What laboratory technique is commonly used to identify abnormal blood cell populations in suspected leukemia?

Flow cytometry

What is the key challenge the immune system faces with respect to naïve lymphocytes and antigen recognition?

Only a very small fraction (≈1 in 100,000–1,000,000) of naïve lymphocytes specific for any given antigen must locate that antigen

Name two mechanisms by which secondary lymphoid organs help overcome this challenge.

Concentrate antigens at common entry sites and facilitate recirculation of naïve lymphocytes for antigen encounter

What is the primary function of lymph-node reticuloendothelial (phagocytic) cells?

To remove microorganisms and other particles from lymph via phagocytosis

Bone marrow is found in which bones?

Long (femur, humerus) and flat (pelvis, sternum, ribs) bones

Aids negative selection of self-reactive T cells in medulla

Epithelial cells, Hassall’s corpuscles