The Immune Response

Question 1

After initial exposure to antibody

Answer 1

• after initial exposure there is a lag, inductive, or latent phases
• antibody production begins and the rate of production increases resulting in a logarithmic or exponential increase in antibody concentration
• peak antibody concentration is reached and the concentration reaches steady state
• the final stage is a decay or decline phase followed by an extended period of time when a small amount of antibody can be detected

Question 2

Secondary or memory response

Answer 2

• a shorter lag time
• higher rates of antibody synthesis
• highest peak of antibody titer
• longer persistence of antibody
• a predominance of IgG class molecules (instead of just IgM initially)
• higher affinity of antibody
• requires less antigen

Question 3

B-cells

Answer 3

• B- lymphocytes express surface immunoglobin
• each B cell is only able to express a single variable region or idiotype
• the total population of B cells makes up the repertoire of antibody specificities
• antigen is seen by B-cells and those cells with the complementary Ig sequence will respond
• with T cell help the Bcell will proliferate
• there is clonal expansion of the responsive cells

-as immune response continues there is an increase in affinity of the antibody produced- selective expansion

Question 4

Helper T cells

Answer 4

• surface antigen CD4
• Hapten-Carrier experiments-the helper T cell recognizes the protein carrier molecule while the B cell recognizes the hapten or sometimes the carrier
• T cells react with the antigen on the surface of the antigen presenting cell (APC) in response to antigen in the MHC and co-stimulatory molecules
• these T cells then proliferate and produce factors that stimulate B cells
• B cells respond to T cells and differentiate into plasma cells, produce IgGs,and sometimes go into memory B cells instead

Question 5

T-independent antigens

Answer 5

• generally polymeric molecules having a large number of repeating subunits that can perhaps cause a cross linking of the immunoglobulin on the B cells
• other T independent antigens are polyclonal activators of B cells that provide a mitogenic signal to the B cell that a T cell normally would

Question 6

Antigen presenting cells (APCs)

Answer 6

• initiate the interaction with antigen by endocytosis or phagocytosis
• this may be enhanced by interactiong with complement (C3b receptor mediated), with pre-existing antibody or with specific receptors that recognize pathogens
• after uptake the antigen is processed and presented on the surface of the presenting cell
• this is an immunogenic form of the antigen
• antigen is presented by cells that have MHC
• has to provide a second or co-stimulatory signal- such as B-7 which interacts with CD28 on T cell
• usually dendritic cells or langerhands cells

Question 7

Definition of APC

Answer 7

1) take up and process antigen
2) have MHC II antigen on surface
3) present the antigen with the MHCII antigen
4) provide a co-stimulatory signal (B7)