Lecture 24: Immune/Lymphatic System I

Question 1

Innate Immunity

Answer 1

“Born with it”; lacks immune specificity and memory, inflammatory response

Question 2

Acquired Immunity

Answer 2

Takes longer to develop and develops in response to antigens; more powerful than innate immunity and displays specificity and memory

Question 3

Passive Immunity

Answer 3

Temporary immunity due to donated antibodies; ex: transplacental passing of maternal antibodies to fetus

Question 4

Active immunity

Answer 4

Long lasting/permanent immunity due to self-exposure to antigen; results in memory T cells and B cells specific for antigens

Question 5

Primary lymphoid organs

Answer 5

Thymus and Bone marrow: precursor cells mature into immunocompetent cells; each cell is programmed to recognize a specific antigen; lymphocytes originate here

Question 6

Secondary lymphoid organs

Answer 6

Lymph nodes, spleen, tonsils; trapped antigens stimulate clonal expansions of mature T and B cells; lymphocytes reside here

Question 7

Primary lymph follicle/nodule

Answer 7

Spherical, tightly packed accumulations of virgin B cells and dendritic reticular cells that have NOT been exposed to antigens

Question 8

Secondary lymph follicle/nodule

Answer 8

Derived from PRIMARY follicles that HAVE been exposed to foreign antigens; these are not present at birth; Structurally: contain a corona (dark, peripheral region composed of densely packed B lymphocytes) and germinal center (central lighter stained region w/ B lymphocytes, memory B cells, plasma cells, dendritic reticular cells which function as antigen-presenting cells)

Question 9

Diffuse vs. Aggregated Lymphatic Tissue

Answer 9

Diffuse=scattered clusters of cells located in the connective tissue stroma; ex: MALT/BALT/GALT

Aggregated=beneath and in contact with epithelium; ex: Peyer’s patches (ileum) and tonsils

Question 10

Antibodies (Immunoglobulins)

Answer 10

5 classes: IgA, IgD, IgG, IgM, IgE; 2 heavy/2 light chains, Fab fragment responsible for diversity, Fc fragment determines class of antibody

Question 11

Major Histocompatibility Complex (MHC)

Answer 11

Main function: Presentation of antigenic peptides to T-cells; 2 classes

Question 12

MHC I

Answer 12

Expressed on surface of all cells EXCEPT trophoblast and RBCs; CD8+ T cells recognize peptide fragments of foreign proteins bound to MHC I

Question 13

MHC II

Answer 13

Expressed on surface of B cells and antigen-presenting cells; CD4+ T cells recognize fragments of foreign protein fragments bound to MHC II

Question 14

CD4+ T cells

Answer 14

Recognize antigens bound to MHC class II molecules; Helper cells: assist CD8+ cell differentiation and B cell differentiation

Question 15

CD8+ T cells

Answer 15

Cytolytic T-cells: bind to antigen presenting cell and undergo mitosis; release perforins (punch holes in cell membranes) and Fas ligand (cause apoptosis)

Recognize antigens bound to MHC class I molecules, mediators of cellular immunity

Question 16

CD16+ T cells

Answer 16

“Natural Killer” NK T cells: activated by tumor cell antigens and release cytokines: Interleukin-2, Interferon-gamma, macrophage activating factor, chemotactic factor, tumor necrosis factor

Question 17

What is the most important opsonin in the complement cascade?

Answer 17

C3b = makes antigen attractive to macrophages

Question 18

What are the results of the Complement cascade?

Answer 18

Activation of the membrane attack complex (MAC) on pathogen leading to perforations/lysis, production of opsonins (coatings that make antigens more palatable to phagocytes), release of chemokines which attract phagocytes to areas of infection/inflammation

Question 19

Parenchyma

Answer 19

Consists of cells that typically pack areas of lymphoid organ (mostly lymphocytes)

Question 20

Stroma

Answer 20

Consists mostly of reticular fibers and cells, including undifferentiated cells and fixed and free macrophages

Question 21

Hilus of lymph node

Answer 21

Entry/exit point for vessels - sets up circulation pattern

Question 22

Capsule of lymph node

Answer 22

dense collagen fibers, some elastic fibers and smooth muscle fibers

Question 23

Cortex of lymph node

Answer 23

Outer area is bone marrow affiliated and contains lymph follicles; Follicles contain B cells, follicular dendritic cells, migrating dendritic cells, Secondary = mantle, germinal layer, Primary = lack mantle and germinal center

Deep area: contains T helper cells, macrophages, and HEVs

Question 24

Medulla of lymph node

Answer 24

Irregular arrangement of loose medullary sinuses and dense medullary cords; sinuses lined with macrophages, cords consist of blood vessels/lymphoblasts/plasma cells; site of lymphocyte reentry into lymph stream; thymic-dependent areas in subcortical and deep medullary region