5.12 - Active, passive, natural and artificial immunity

Active immunity

• Long-lasting adaptive immunity that is acquired when the body is exposed to antigens

• The body develops memory B and T cells from the immune response, allowing for a stronger, faster immune response when the antigen is encountered again

• Takes time to acquire immunity

Passive immunity

• Temporary immunity that boosts the body’s defence for a short period of time

• Instead of undergoing an active immune response, an organism receives antibodies produced by another organism, meaning memory cells are not produced

• Immunity is acquired immediately

Natural passive immunity

A natural process where antibodies are produced by another organism and passed to a recipient who has not gone through an adaptive immune response

Examples of natural passive immunity

• Transfer of antibodies from mother to foetus across the placenta

• Transfer of antibodies from mother to baby through breastfeeding

Artificial passive immunity

• A recipient receives an injection of antibodies that have been produced by another organism

• The injection is usually called antiserum, which is a fluid portion of the blood that contains antibodies

• Antibodies bind to the antigen, neutralising or inhibiting them, which gives the body time to mount an adaptive immune response

Example of artificial passive immunity

• A person bitten by a snake is likely to die from the venom before their body can mount an adaptive immune response to the antigen

• Antivenom is produced by injecting a horse with venom, causing it to produce antibodies without experiencing adverse effects. These antibodies are extracted and used to make antivenom.

• Antivenom is injected into the recipient, providing them with antibodies that neutralise the antigens

Natural active immunity

• The person gets sick naturally and mounts an adaptive immune response against the antigen

• Memory cells are developed which allows for a faster, stronger immune response when the antigen is encountered again

Example of natural active immunity

• A person encounters chicken pox as a child, causing them to undergo an adaptive immune response, producing B cells and T cells to kill the chickenpox antigens

• Memory B and T cells remain in the body after the infection, allowing for a faster, stronger immune response if chickenpox antigens are encountered again

Artificial active immunity

A vaccination that causes an adaptive immune response to produce memory cells

Vaccinations are artificially made injections that contain:

• Altered microorganisms

• Attenuated (weakened) microorganisms

• Dead microorganisms

• Inactivated forms of proteins or toxins (subunits)

• RNA that codes for antigenic proteins that are produced in body cells and displayed on MHC-I markers

Live attenuated vaccines

• Involves a living microbe that has been weakened in the lab

• Usually provides long-lasting immunity because it produces a stronger adaptive immune response

• It produces multiple types of B memory cells due to the multiple antigens present

• Can cause disease in individuals with weak immune systems

Inactivated vaccines

• Involves dead microbes killed by heat, radiation or chemicals

• Contain multiple antigens

• Weaker response than live attenuated vaccines and therefore require boosters

Subunit vaccines

• Only contain parts of the microbe

• Single antigen, multiple antigens, detoxified toxins

• Safer and more stable than live vaccines and easier to store

• Require multiple doses to strengthen the immune response

RNA vaccines

• The vaccine contains mRNA code that codes for the antigenic protein of the pathogen

• mRNA enters body cells and produces the antigenic proteins which are expressed on MHC-I markers

• Safer for patient, cheaper and faster to produce-

Herd immunity

Herd immunity is a form of immunity that occurs when a significant portion of a population is vaccinated, providing protection for individuals who have not developed immunity

• The more people vaccinated, the less chance of an infectious disease spreading throughout a population

• Herd immunity is essential for protecting people who cannot be vaccinated or have suppressed immune systems