Types of immunity

Immunity can be specific and non-specific:

Specific Immunity

In this study session, we will focus on specific immunity, which is the type generated by immunisation. Specific immunity is produced when the immune system reacts with specifically against one particular type of infectious agent. Specific immunity can be naturally acquired, or artificially acquired - in both cases through either "active" or "passive" mechanisms. In this section, we will briefly distinguish between these four types of specific immunity.

Non-Specific Immunity

Non-specific immunity (also known as innate immunity - "innate" means "already formed at birth") includes protection from infectious agents by mechanical barriers, such as intact skin or the mucus membranes lining the inside of our nose, mouth, lungs, reproductive system and gut. It also includes the actions of some kinds of white blood cells that can engulf ("eat") or kill a wide range of infectious agents, without distinguishing between them.

Types of Specific Immunity

I. Naturally Acquired Immunity

Naturally acquired immunity occurs "naturally" without any intervention from a health professional. The difference between the "active" and the "passive" forms depends on whether the immune person makes the antibodies themselves (actively), or gets them from someone else (passively).

Naturally acquired active immunity

Naturally acquired active immunity occurs after an infection activates the person's immune system. For example, non-immunized children who develop measles and recover from the illness, get better because they have made an effective immune response against the measles virus. As a result, they acquire protection from measles for the rest of their lives (i.e. they are immune to measles). They have naturally acquired active immunity because the protection developed naturally in their bodies, without a vaccine being given.

The immunity is active because the children produced their own antibodies and memory cells, which specifically attack any invading measles viruses they meet in the future.

Naturally acquired passive immunity

Naturally acquired passive immunity occurs when a mother gives her own antibodies to her baby, transferring them from her blood to the fetal blood across the placenta, or giving them to the baby in her breast milk. The immunity created by these maternal antibodies is naturally acquired from the mother (without any medical intervention). During the first few months of a baby's life, until the mother stops breastfeeding, her antibodies provide passive protection to the baby against infectious agents that the mother has encountered during her own life. The term "passive" is used because the baby didn't produce the antibodies itself. The active production of antibodies by the immune system of the baby takes several years to develop properly.

Do you know that the tetanus vaccine given to a mother during antenatal care will also protect the newborn infant from tetanus for the first few weeks or months of its life? This is because the maternal antibodies against tetanus bacteria cross the placenta and get into the fetus.

II. Artificially Acquired Immunity

In artificially acquired immunity the person must be artificially and intentionally exposed to foreign antigens (actively), or given someone else's antibodies (passively), in order to generate a protective immune response.

Artificially acquired active immunity

Artificially acquired active immunity is protection produced by intentional exposure of a person to antigens in a vaccine, so as to produce an active and lasting immune response. The antigens in the vaccine stimulate the immune system to produce antibodies and memory cells which are specifically directed against the antigens in the vaccine. After the immunisation, if the living infectious agents with the same antigens that were in the vaccine get into the person's body, the correct antibodies are already present, and they bind to the infectious agents. The memory cells generate a rapid immune response from the rest of the immune system, and the infectious agents are quickly attacked and destroyed, often before symptoms of the disease can develop.

Artificially acquired passive immunity

Artificially acquired passive immunity is protection acquired by giving a person an injection or transfusion of antibodies made by someone else. These antibodies neutralise the infectious agents in the usual way, but the protection lasts only a few weeks because the antibodies gradually break down and are not replaced. In artificial passive immunisation there is no involvement of the person's own immune system.