Antibodies and vaccination

Biology AS · Immunity. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

Test this topic free All Biology AS topics

The idea

An antibody is a globular glycoprotein made by plasma cells. It has four polypeptide chains, two heavy and two light, held together by disulfide bonds. The variable regions form two binding sites with a shape complementary to one antigen. The constant region is the same in every antibody of one class.

Monoclonal antibodies are identical antibodies from one clone of cells. They are made by fusing plasma cells with myeloma cells to give hybridoma cells, which divide and secrete one antibody.

Immunity is active when your own body makes the antibodies and memory cells, and passive when you receive antibodies made elsewhere. A vaccine contains antigens and gives artificial active immunity.

Rules to remember

Antibody actions: agglutination (clumping pathogens), neutralising toxins, blocking pathogens from entering cells, and marking pathogens for phagocytes.
Hinge region: gives flexibility, so the two sites can bind antigens at different distances apart.
Hybridoma method: inject a mouse with the antigen, take plasma cells from its spleen, fuse them with myeloma cells, select and clone the hybridoma that makes the antibody wanted.
Monoclonal antibodies in diagnosis: labelled antibodies show where an antigen is, as in pregnancy tests. In treatment: they bind to one target, such as a receptor on cancer cells.
Active immunity: slow to start, memory cells made, long-lasting. Passive immunity: immediate, no memory cells, short-lived.
Natural: by infection, or from mother across the placenta or in milk. Artificial: by vaccination or by injection of antibodies.
Herd immunity: when most people are immune, the pathogen is rarely passed on, so the unvaccinated are protected too.

Common mistake

Saying a vaccine contains antibodies. A vaccine contains antigens; the body makes its own antibodies and memory cells in response.

Worked example

A child catches chickenpox, recovers, and does not catch it again when exposed years later. What type of immunity is this?

The child's own lymphocytes responded to the antigens and made antibodies and memory cells, so it is active.
The antigens entered by a normal infection, not by vaccination, so it is natural.
Memory cells last for years, which explains the protection later.

Answer: Natural active immunity.

Ask about this

Type what you are stuck on. The helper finds the explanation, worked examples and the notes to read, free and instant.

Read the full notes

Full-course notes

Keep going

← The immune system Take a Biology AS test