Intro to Acquired Immunity

Question 1

What is the function of secondary lymphoid organs?

Answer 1

To concentrate antigens that are introduced through common portals of entry such as the skin, respiratory tract, and GI tract.

Question 2

Antigen that is present in the blood will typically initiate an adaptive immune response in what secondary lymphoid organ?

Answer 2

The spleen

Question 3

Describe which the responding lymphocytes, their effector mechanisms, how the effectors will be transferred, and overall function of the effectors, will be to the following 3 microbes: extracellular microbes, phagocytosed microbes in macrophages, and intracellular microbes (including viruses)

Answer 3

Extracellular microbes: B lymphocytes, secreted antibody, transferred by serum, overall function is to neutralize and opsonize thus blocking and eliminating an infection

Phagocytosed microbes in macrophages: Helper (CD4) T lymphocytes, secrete cytokines, transferred by cells, overall function is to activate macrophages to destroy phagocytosed microbes

Intracellular microbes: Cytotoxic (CD8) T lymphocytes, triggering of death ligand or perforin/granzyme, transferred by cells, overall function is kill infected host cells and eliminate reservoirs of the infection

Question 4

What are B cells stimulated by?

Answer 4

B cells respond to both protein and non-protein antigen but depending on the subset of B cells they will respond preferentially

Question 5

How are T Helper lymphocytes responsible for mounting and executing an adaptive immune response?

Answer 5

They make cytokines that regulate afferent (generation) and efferent (effecting response) arms of the response. They are specifically involved in stimulating the production of antibodies as well as generation of cell mediated immune responses

Question 6

What is the component that forms that molecular basis for antigen-specificity on the B cells and T cells. How do the structures and specificities differ between the two?

Answer 6

B Cells: have surface Ig which is composed of 2 heavy chains and 2 light chains with an antigen binding region in the hypervariable region of both the light chains and the heavy chains and constant region just in the heavy chains. They have ~10^9 specificities

T Cells: have T-cell receptor (TCR) composed of a heterodimer of alpha and beta chains both of which have variable (located at N-term), constant regions, and a transmembrane domain with very little cytoplasmic domain. They have ~10^11 specificities

Question 7

Why do transplants not work well or require the use of immunosuppresents?

Answer 7

This is because TCR can only recognize antigen being presented to it within the context of the person’s own and unique MHC.
MHC has a polymorphic residue that TCR must recognize in order for it to detect the antigen being presented to it

Question 8

Most (~85% of TCRs) are made of the alpha and beta chains however a small amount of T lymphocytes contain a TCR made of other chains. Describe these chains and how they differ from the the alpha/beta TCRs and where the T lymphocytes may function.

Answer 8

Minority of T lymphocytes have the gamma/delta heterodimer TCR. It has a much more limited diversity in antigen specificity and can recognize non-peptide antigens without MHC.
This may be important first line of defense in the skin and gut

Question 9

What are 3 types of specific immunity and their corresponding subclasses?

Answer 9

1. Active (something you made yourself): either natural (via infection) or artificial (via vaccination)
2. Passive (someone else gave you the immunity): either natural (via transplacental or colostral/breast milk transfer of antibody) or artificial (administration of pooled Ig
3. Adoptive: transfer of immune cells (this is mostly done experimentally on mice)

Question 10

Specificity is the basis of what theory?

Answer 10

Clonal selection theory

Question 11

Though the antigen-specificity variability for alpha/beta TCR is ~10^11 this does not mean they recognize that many antigens. How many antigens can a T lymphocyte recognize?

Answer 11

About 1 billion or 10^9

Question 12

What are the 8 cardinal features of an adaptive immune response? Give a brief description for each

Answer 12

1. Specificity: Immune response is specific for distinct antigens
2. Diversity: Total number of antigen specificities is very large
3. Adaptability: Able to respond to antigens not previously encountered in nature
4. Memory: Exposure of immune system to foreign antigen enhances its ability to respond again with a secondary response being faster, larger, and qualitatively different
5. Clonal Expansion: Increase in the number of antigen-specific lymphocytes to keep pace with pathogen during an infection
6. Specialization: Generation of an optimal response for defense against different microbes
7. Self Limitation (Contraction and Homeostasis): Immune response decreases over time, effector cells are short lived, contain regulatory feedback elements
8. Discrimination of self from non-self

Question 13

What is the frequency of lymphocytes for any given specific antigen?

Answer 13

Approximately 1 in 1 million

Question 14

For a primary adaptive immune response how long does it take to mount and how long till it peaks?

Answer 14

5-10 days to mount the response and about 14 days till it peaks

Question 15

What are the 4 tenants of the Clonal Selection Theory?

Answer 15

1. Every individual contains numerous clonally derived lymphocytes
2. Each lymphocyte has an antigen receptor specific for a single antigen
3. These are present prior to exposure to antigen
4. Antigen selects a pre-existing clone and activates it