Anatomy and Physiology of the Immune System

Question 1

1. Define: leukocytes, mononuclear cells, polymorphonuclear cells, granulocytes, mast cells, plasma and serum.

Answer 1

leukocytes:
– nucleated, white blood cells. They are in the buffy coat.
mononuclear cells:
– leukocytes whose nucleus has smooth outline –> become monocytes and lymphocytes.

polymorphonuclear cells:
– cells that have lobulated nuclei (aka granulocytes) –> basophils (related to mast cells), eosinophils, and neutrophils.
Granulocytes: -cells with granules in their cytoplasm, see above.

mast cells:
– basophils, kind of, but found in tissue instead of plasma. Involved with type I immunopathology (immediate hypersensitivity)

plasma and serum:
– plasma = blood without the actual cells; serum = plasma without clotting factors.

Question 2

2. Sketch schematically a neutrophil; eosinophil; basophil; small lymphocyte; lymphoblast; plasma cell; monocyte. Include the characteristic features which are used to distinguish each cell type.

Answer 2

• Lymphocyte has round nucleus without much cytoplasm.
• Lymphoblast has a big nucleus but with a bit more cytoplasm.
• Plasma cells (differentiated B cells) have big nuclei with lots of protein product (ribosomes stain blue).
• Neutrophils have lobulated nuclei with granules.
• Eosinophils have lobular nuclei and orange granules.
• Basophils have lobular nuclei (harder to see) and dark blue-black granules.
• Monocytes have vacuoles, bigger nuclei, and lots of cytoplasm, some granules.

Question 3

3. 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/uL).

Answer 3

-Total WBCs = 4,500-10,500 per microliter of blood (x109).

• Neutrophils = 40-60% (1.8-8.8 x109).
• Eosinophils = 1-4% ( 0-0.66 x109).
• Basophils = 0.5-1% (0-0.22 x109) and monocytes = 2-8% (0.9-1.21 x109).

-Lymphocytes = 20-40% (0.8-5.5 x109). These counts may be higher in children.

Question 4

4. Name the major central and peripheral lymphoid organs.

Answer 4

Central organs:
-Where lymphocytes develop = bone marrow and thymus.

Peripheral organs:

• Where lymphocytes do their job = lymph nodes, spleen, tonsils, adenoids, and Peyer’s patches in the small intestine.
• Gut encounters so much foreign stuff, and patches line the intestine so they can rapidly decide if something is commensal or dangerous if they need to trigger an immune response.
• Functional structure of Peyer’s patches include specialized mucosal M cells = gatekeepers that ingest proteins and transport them to the abluminal side where DC’s can take the antigens to the B cell follicles and T cell zones.

Spleen:

• has red pulp contains lots of phagocytic cells and makes RBCs when necessary.
• Also filters particulates and stores monocytes.
• White pulp = cell islands.

Question 5

5. 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 5

• Lymphocytes move in blood to get to destination faster.
• Lymphatics dump into nodes that move towards heart, and culminate at thoracic duct that dumps into heart where lymph is added back into circulation.
• Lymph nodes have a hilum through which blood enters and exits, where you get crossing over between blood and lymph.
• Incoming lymph at the afferent lymph –> comes in at the periphery and percolates at the node, leaving via efferent lymph or in blood.
• Cortex = outside of lymph node (has lymphoid follicles) and deeper = deep or paracortex, which is dense with lymphocytes so antigens get shown to as many cells possible.
• Cells in cortex = B;
• cells in paracortex = T.
• Pattern of recirculation is when lymphocyte encounters cells lining postcapillary venules in the lymph nodes and the endothelial cells lining the venules are high and cuboidal –> have molecules on their surfaces that lymphocytes can interact with to leave blood and enter lymph.
• This allows lymphocytes to get distributed throughout the body –> immunological memory happens via activated cells that spread out beyond the wound site.

Question 6

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

Answer 6

• Antigen is something that interacts with the immune response;
• Immunogen is an antigen that can give rise to an immune response, actually creates it.
• Tolerogen = form of antigen that would not provoke an immune response and would prevent development of a future immune response.
• The part of an antigen that fits into the receptor on a B or T cell lymphocyte = the antigenic determinant/epitope.

Question 7

7. 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 7

-Lymphocytes have receptors, each for a specific antigen.
-T cell receptors = alpha and beta chains;
-B cell receptors = antibodies.
-Bind the antigenic determinant/epitope –> if correctly binds, cell is activated and proliferates.
-Cells can also differentiate into effectors (B cells –> blasts and plasma cells; helper T –> cytokines, killer T –> kill targets) and memory cells.
-Can’t just have epitope binding though –> the right accessory interactions between T cell and dendritic cell have to happen, as well as a good fit.
-Then T cell gets activated.
-This is important because don’t want to rapidly divide the wrong kind of cell, so need other signals beyond just antigen-recognition.
(Graph would theoretically look exponential.)

Clones = amplified immune response.