Immuno: A&P of Immune Sys

Question 1

Define: leukocytes

Answer 1

WBCs (nucleated cells of the blood)

Question 2

Define: mononuclear cells

Answer 2

Leukocytes with smooth, rounded nuclei. When pathologists look at tissue, can’t tell if round nuclear cell is lymphocyte or monocyte (immature mac), so it’s described as mononuclear cell

Question 3

Define: PMNs

Answer 3

Cells whose nucleus is lobulated, also called granulocytes because they have (usually) rather prominent cytoplasmic granules. They are: eosinophils, basophils, and neutrophils

Question 4

Define: mast cells

Answer 4

Granulocyte containing many granules rich in histamine and heparin. Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being intimately involved in wound healing and defense against pathogens.

Question 5

Define: plasma and serum

Answer 5

Whole blood - cells = plasma

plasma - clotting factors = serum

Question 6

List the normal adult white cell count and differential percentages. From these, calculate absolute counts for the different cell types (as cells of that type /μL).

Answer 6

Normal adult total white cell count: 4.5 - 11 x 109/L
Neutrophil count: 1.8 - 8.8 x 109/L (40-80%)
Lymphocyte count: 0.9 - 5.5 x 109/L (20-50%)
Basophil count: 0 - 0.22 x 109/L (0-2%)
Eosinophil count: 0 - 0.66 x 109/L (0-6%)
Monocyte count: 0.09 -1.21 x 109/L (2-11%)

Question 7

Name the major central and peripheral lymphoid organs.

Answer 7

Central: bone marrow and the thymus (where lymphocytes develop). In mammalian embryo, bone marrow function is first found in the yolk sac and then in the liver

Peripheral: lymph nodes, spleen, Peyer’s patches and mesenteric lymph nodes of the gut, tonsils and adenoids (where mature cells are organized to trap and respond to foreign invaders)

Question 8

Describe the recirculation of lymphocytes from blood to lymph and back; include in your discussion the specialized features of lymph node blood vessel endothelium that permit recirculation.

Answer 8

• A lymphocyte in the blood encounters the cells lining certain PCVs in the peripheral lymphoid tissues, especially lymph nodes.
• These endothelial cells are unusual not flat as is the usual case, but high and cuboidal.
• Recirculating lymphocytes may bind to and pass between the endothelial cells into the lymph node, where they may stay, or move eventually into the lymph which drains from that lymph node to the next in the chain.
• Lymph works its way into the largest lymph channels such as the thoracic duct near the heart; from there it is emptied into the venous blood and the circulatory loop can start over again.
• Thus there are two lymphocyte circulations, blood and lymphatic, in which lymphocytes cross from blood to lymph at the nodes, and from lymph back to blood at the heart.

Question 9

Define antigen, and compare it to immunogen. Define antigenic determinant and epitope.

Answer 9

Antigen: anything that can be recognized by the immune system
Immunogen: anything that can actually stimulate an immune response
Antigenic determinant = epitope = the part of an antigen that fits into the receptor is the antigenic determinant or epitope

Question 10

Discuss lymphocyte activation by antigen with respect to: receptor binding, proliferation, differentiation. Draw a graph showing relative time on one axis and relative lymphocyte numbers on the other, in response to antigen administration.

Answer 10

Receptor binding: the fit between receptor and the antigen it sees must be good (specific) enough, several nearby receptors must be simultaneously bound by antigen, and other cell surface molecules must be involved too (accessory interactions or costimulation). Once the cell is correctly activated it begins to proliferate.
Proliferation: Lymphocytes can divide as fast as every 6 hours, so in just a few days you have thousands of cells specific for the antigen that got the process started. These cells also differentiate
Differentiation: into effectors that do the job (B cell blasts and plasma cells that release antibodies into the blood; helper T cells that pour out cytokines; killer T cells that induce their targets to die) and into memory cells that recirculate efficiently and are very easily triggered by another exposure to antigen.

Question 11

Distinguish between “humoral” (antibody-mediated) and cell-mediated immunity in terms of: the types of lymphocytes involved, the nature of the molecules they release when activated, the types of inflammatory cells they preferentially involve.

Answer 11

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Question 12

Discuss the DC’s path through a LN

Answer 12

Arterioles enter at the hilum, and split up into capillaries which drain into venules (the ones with the high cuboidal endothelium); veins exit at the hilum.

Lymph channels enter at the periphery. Lymph flows into the subcapsular sinus, percolates through the substance of the node and leaves in efferent lymphatics via the hilum.

►The node’s outer region is called the cortex, and it is full of tightly packed (but highly motile) lymphocytes arranged in follicles.

Frequent very dense areas with many dividing cells can be seen in the cortex; ►these are called germinal centers and represent visible evidence of an immune response.

The deep or paracortex is a little less dense, but still has huge numbers of lymphocytes.

Dendritic cells that arrive in the afferent lymph tend to gather at the interface between the cortex (mostly B cells, arising from the bone marrow) and the paracortex (mostly T cells, arising from the thymus).

Follicular helper T cells (Tfh) migrate from the deep cortex into the follicles where they help B cells get activated.