1-28 The Immune Response

Question 1

What are the phases of the primary immune response?

Answer 1

• Lag phase: AKA inductive/latent phase; no antibody can be detected
• Log phase: exponential increase in antibody concentration
• Steady state: peak antibody concentration
• Decay phase: declining antibody concentration
• Lastly, extended period of time when a small amount of antibody can be detected

Question 2

How is the secondary immune response different from the primary immune response?

Answer 2

• Shorter lag time
• Higher rates of antibody synthesis
• Higher peak of antibody titer
• Longer persistence of antibody
• Predominance of IgG class molecules
• Higher antibody affinity
• Requires less antigen

Question 3

What is the role of B-cells in the immune response?

Answer 3

The total population of B-cells, each with their own idiotype, make up the repertoire of antibody specificities. They recognize antigens and harness T-cells to proliferate the B-cells with the complementary Ig sequence (clonal expansion).

As the immune response continues, there is an increase in the affinity of antibodies being produced.

Question 4

What is the role of helper T-cells in the immune response?

Answer 4

T-cells recognize antigens and different parts of antigens than B-cells; most T-cells react to protein or peptide antigens. In response to antigen (+MHC) and co-stimulatory molecules, T-cells proliferate and produce factors that stimulate B-cells.

Some T-cells’ factors are responsible for the switch from IgM production to IgG production.

Question 5

What are T-independent antigens?

Answer 5

Antigens that can possibly cause B-cell immunoglobulin to cross-link. Generally polymeric, with large numbers of repeating subunits.

Others are polyclonal activators of B-cells; they provide a mitogenic signal that would have been provided by T-cells.

Question 6

What are the necessary features of antigen presenting cells (APCs)?

Answer 6

• Must take up and process antigen
• Must have MHC class II antigen on its surface
• Must present the antigen with the MHC class II antigen
• Must provide a co-stimulatory signal (B7)

Without a co-stimulatory signal, APCs cannot induce immunity.