Unit 4 - Immune System PART N & O

Question 1

T-cell and B-cell receptors (TCRs and BCRs)…

Answer 1

are all made randomly via DNA cutting and recombination processes. So there is a small chance of producing TCR or BCRs that are self-reactive (i.e. react to self-antigen)

Question 2

Usually, antigen recognition by TCR and BCR leads to…

Answer 2

an immune response

Question 3

If self-antigen is recognized (i.e. if BCRs or TCRs can bind to self- antigen), the result is…

Answer 3

autoimmunity. E.g. Type-1-diabetes, body produces islet cell antibodies that destroy the insulin producing cells in the pancreas.

Question 4

Before attempting any other function, the immune system must accomplish 1 task 1st…

Answer 4

distinguish its own cells from foreign cells

Question 5

The lack of immune response by lymphocytes to cells of the body is known as…

Answer 5

SELF-TOLERANCE, & it begins during embryonic dev.

- the specificity of lymphocytes clones resides in the proteins that become cell surface receptors or antibodies

Question 6

When self-tolerance fails…

Answer 6

the body makes antibodies against its own components through T cell-activated B lymphocytes

• body’s attack on its own cells lead to AUTOIMMUNE DISEASES
• antibodies produced in autoimmune diseases are specific against a particular organ or tissue type

Question 7

Why does self-tolerance suddenly fail?

Answer 7

not 100% sure, but…

• autoimmune diseases often begin in association with an infection
• 1 potential trigger for autoimmune diseases is foreign antibodies that are similar to human antigens
• when the body makes antibodies to the foreign antigen, those antibodies have enough cross-reactivity with human tissues to do some damage

Question 8

During maturation,

Answer 8

T-cell clones and B-cell clones have their TCR or BCR tested against self-antigen. Cells whose TCRs or BCRs recognize self-antigen either destroyed or inactivated.

Question 9

During maturation, T-cell clones and B-cell clones have their TCR or BCR tested against self-antigen. Cells whose TCRs or BCRs recognize self-antigen either destroyed or inactivated.

Answer 9

1. Clonal deletion

2. Clonal inactivation (anergy)

Question 10

Clonal deletion

Answer 10

occurs in thymus (T-cells) bone marrow (B-cells) during fetal period up to a short time after birth. Can also occur in the peripheral tissues/circulation.

a. As T-cells and B-cells are produced, they are presented with self- antigens.
b. If there is no recognition by the TCR/BCR, those cells “escape” into circulation.
c. If self-antigen is recognized (i.e. binds to the TCR or BCR) then that clone undergoes apoptosis (dies) and so is deleted.

Question 11

Clonal inactivation (anergy)

Answer 11

occurs only in the tissues and circulation. Causes self reacting cells to become non-responsive.

Question 12

Allergy (Immediate Hypersensitivity)

Answer 12

Overactive response to an antigen

On first exposure, allergen activates pathways that create memory B cells and plasma B cells. The plasma B cells produce IgE antibodies.

IgE becomes bound to Mast cells.

Upon subsequent exposure, the allergen interacts with IgE antibodies on mast cells, and large amounts of histamine and other proinflammatory cytokines are released.

Creates a local inflammatory response in area of contact with allergen, and will observe redness, swelling, heat, itch, etc. (e.g. hives)

Question 13

Allergy

Answer 13

an inflammatory immune response to a nonpathogenic antigen

Question 14

Immediate Hypersensitivity

Answer 14

are mediated by antibodies & occur within mins of exposure to ALLERGENS