Question

“An individual receives a vaccine that is composed of a killed virus, which includes just the viral antigens left over. Describe the events that follow, leading to antibody production in the patient. Describe all the players involved in this humoral immune response, and their interactions with each other”

Answer 1

After you have been vaccinated, some of the cells that are responsible for protecting you against disease — your B lymphocytes — detect the antigens in the vaccine. The B lymphocytes will react as if the real infectious organism was invading your body. They multiply to form an army of identical cells that are able to respond to the antigens in the vaccine. The cloned cells then evolve into one of 2 types of cells:

• plasma cells; or
• memory B cells.

The plasma cells produce antibodies (Y- or T-shaped molecules), which are trained specifically to attach to and inactivate the organism you are being vaccinated against.

This response from your immune system, generated by the B lymphocytes, is known as the primary response. It takes several days to build to maximum intensity, and the antibody concentration in the blood peaks at about 14 days.

Your body continues making antibodies and memory B cells for a couple of weeks after vaccination. Over time, the antibodies will gradually disappear, but the memory B cells will remain dormant in your body for many years.

The memory B cells (as the name implies) keep a memory of the organism that you were vaccinated against. If you are ever exposed to that organism, the dormant memory cells will recognise it straight away, and rapidly start multiplying and developing into plasma cells. Because the plasma cells have already been trained to produce antibodies against the organism, they are able to produce a large number of antibodies very quickly (within hours).

The antibodies attach to the invading organisms and prevent them from attacking your healthy cells. And because the antibodies are produced so quickly, they are able to fight the disease before you even get sick.

This accelerated and more intense immune response generated by the memory B cells is known as the secondary response. It is faster and more effective because all the preparations for the attack were made when you were vaccinated.

The humoral immune response takes place in blood and lymph:

B Cell Activation

B cells must be activated by an antigen before they can fight pathogens. First, a B cell encounters its matching antigen and engulfs it. The B cell then displays fragments of the antigen on its surface. This attracts a helper T cell. The helper T cell binds to the B cell at the antigen site and releases cytokines that “tell” or signal the B cell to develop into a plasma cell.

Plasma Cells and Antibody Production

Plasma cells are activated B cells that secrete antibodies. Antibodies are large, Y-shaped proteins that recognize and bind to antigens. Plasma cells are like antibody factories, producing many copies of a single type of antibody. The antibodies travel throughout the body in blood and lymph. Each antibody binds to just one kind of antigen. When it does, it forms an antigen-antibody complex. The complex flags the antigen-bearing cell for destruction by phagocytosis.

Memory Cells

Most plasma cells live for just a few days, but some of them live much longer. They may even survive for the lifetime of the individual. Long-living plasma cells are called memory cells. They retain a “memory” of a specific pathogen long after an infection is over. They help launch a rapid response against the pathogen if it invades the body again in the future.