a. In the following graph, at time A the host was injected with tetanus toxoid. Show the response to a booster dose at time B.
b. Draw the antibody response of this same individual to exposure to a new antigen at time B.

Verified step by step guidance

1. Step 1: Understand the context of the problem. The host is first injected with tetanus toxoid at time A, which will initiate a primary immune response. This involves activation of naive B cells, production of IgM antibodies initially, followed by class switching to IgG antibodies, and formation of memory B cells.
2. Step 2: For part (a), consider what happens at time B when a booster dose of the same antigen (tetanus toxoid) is given. The immune system will mount a secondary (anamnestic) response. This response is faster, stronger, and predominantly involves IgG antibodies due to the presence of memory B cells formed during the primary response.
3. Step 3: To draw the antibody response for part (a), start with a smaller, slower rise in antibody levels after time A (primary response), then at time B, show a rapid and higher increase in antibody levels representing the secondary response. The curve after time B should peak higher and faster than after time A.
4. Step 4: For part (b), the individual is exposed to a new antigen at time B. Since this is a new antigen, the immune system will mount a primary response similar to the initial injection at time A. This means a slower rise in antibody levels, starting with IgM and then IgG, with no memory cells to speed up the response.
5. Step 5: To draw the antibody response for part (b), show a slow and gradual increase in antibody levels starting at time B, similar in shape and timing to the primary response seen at time A, but independent of the previous tetanus toxoid response.

Key Concepts

Primary and Secondary Immune Responses

The primary immune response occurs when the immune system first encounters an antigen, producing antibodies slowly and at lower levels. The secondary (or booster) response happens upon re-exposure to the same antigen, leading to a faster and stronger antibody production due to memory B cells formed during the primary response.

Tetanus Toxoid and Vaccination

Tetanus toxoid is an inactivated toxin used as a vaccine to stimulate immunity without causing disease. It primes the immune system to recognize tetanus toxin, enabling a rapid and enhanced antibody response upon subsequent booster doses or exposure to the actual toxin.

Antibody Response to New Antigens

When the immune system encounters a new antigen for the first time, it mounts a primary response characterized by a lag phase before antibody production begins. This response is slower and produces fewer antibodies compared to a secondary response, as memory cells specific to the new antigen have not yet been formed.