Antibodies and vaccination

Hinge region: gives the antibody flexibility, so its two arms can bind around an antigen.

Antigen-binding sites: the variable regions at the tips of the arms; their amino acid sequence folds into a specific 3D shape, so each antibody binds one type of antigen.

Functions of antibodies: attach to bacterial flagella, making the bacteria less active and easier for phagocytes to engulf; cause agglutination (clumping) of bacteria, reducing the chance of spread; punch holes in bacterial cell walls, so the cells burst as they take in water by osmosis.

Antibodies also coat bacteria (opsonisation), making phagocytosis easier because phagocytes carry receptor proteins for antibodies; combine with toxins to neutralise them (antitoxins); and bind to viruses and toxins so they cannot enter or damage cells.

Hybridoma method: B cells that divide by mitosis do not secrete antibodies, and plasma cells that secrete antibodies do not divide. Fusing a plasma cell with a myeloma (cancer) cell gives a hybridoma that does both — it divides indefinitely and secretes one specific antibody, a monoclonal antibody.

Monoclonal antibodies in diagnosis: locating blood clots; locating cancer cells, which carry different cell-surface proteins; identifying the exact strain of virus or bacterium causing an infection, which speeds up treatment.

Monoclonal antibodies in treatment: in breast cancer the antibody binds to cancerous cells and marks them for destruction by the immune system; in rheumatoid arthritis (an autoimmune disease) it binds to proteins secreted by T cells that damage cartilage in joints, blocking their action.

Active Immunity: Your body actively produces its own antibodies and memory cells in response to an antigen. This leads to long-term protection.

• Natural active immunity: Acquired through direct exposure to a pathogen and subsequent recovery from the infection (e.g., getting chickenpox).

• Artificial active immunity: Acquired through vaccination, where antigens are introduced without causing illness.

Passive Immunity: Your body receives pre-formed antibodies from an external source. This provides immediate but short-lived protection as no memory cells are formed.

• Natural passive immunity: Acquired when antibodies are transferred from mother to child across the placenta or via breast milk.

• Artificial passive immunity: Acquired through the injection of antibodies, often for immediate protection against toxins or venoms (e.g., tetanus antitoxin, antivenom).

Vaccination involves introducing a harmless form of a pathogen (e.g., attenuated live pathogen, killed pathogen, isolated antigens, or toxoids) into the body.

This exposure stimulates a primary immune response, where B cells are activated, differentiate into plasma cells (to produce antibodies), and crucially, form memory B and T cells.

The primary response is typically slower and produces fewer antibodies than a secondary response.

Upon subsequent exposure to the actual pathogen, these memory cells trigger a much faster, stronger, and more prolonged secondary immune response, rapidly producing a high concentration of specific antibodies to neutralise the threat before symptoms develop.

Vaccination not only protects individuals but also contributes to 'herd immunity' within a population. This occurs when a sufficiently large proportion of the community is immune, making it difficult for the disease to spread, thereby protecting those who cannot be vaccinated (e.g., infants, immunocompromised individuals).

Vaccination programmes can fail to protect people who suffer from malnutrition: without enough protein they cannot make antibodies or clones of lymphocytes.