Immunity (medicine)

Understanding Immunity: A Journey Through Time

Imagine a world where you could walk through the forest without fear of being poisoned, or where your body could recognize and fight off any invader with ease. That’s what immunity is all about – it’s like having a personal army within you that protects against threats.

The Basics of Immunity

Immunity in biology refers to the state of being resistant or insusceptible to pathogens and infectious diseases. It’s like having a fortress protecting your body from invaders, but this fortress has two layers: innate immunity and adaptive immunity. The innate immunity acts as the first line of defense, providing a semi-specific response against pathogens. Think of it as the initial wall that stops most intruders before they can even get close.

Ancient Solutions to Modern Problems

Over 2000 years ago, people used Mithridate and Theriacum Andromachi to cure poisoning. These concoctions were like ancient vaccines, providing a form of immunity against toxins. The term ‘immunes’ was also found in the epic poem ‘Pharsalia,’ suggesting that even back then, people recognized the concept of being immune.

Medieval and Early Modern Innovations

The miasma theory, which suggested that diseases were caused by bad air, was widely accepted until the 19th century. However, it wasn’t until the discovery of germs/microbes that people began to understand how communicable diseases spread. Ilya Mechnikov developed a full theory of immunity in 1882, laying the groundwork for what we know today.

The Birth of Vaccination

Immunization has existed for over 1000 years, with the Chinese practicing a form of immunization around 1000 AD. Lady Mary Wortley Montagu introduced inoculation into the west in 1721, and Edward Jenner developed the smallpox vaccine in 1798. These were monumental steps that changed the course of human history.

Passive vs Active Immunity

Passive immunity can occur naturally or be induced artificially through antibody transfer. For example, a mother’s antibodies are passed to her fetus starting around the third month of gestation via an FcRn receptor on placental cells. This is like giving your child a head start in life by passing some of your protective abilities.

Artificially acquired passive immunity involves transferring antibodies through human or animal blood plasma, pooled human immunoglobulin, or monoclonal antibodies. It’s used to treat immunodeficiency diseases and certain acute infections but has a short duration and risks of hypersensitivity reactions.

Active Immunity: The Power Within

Active immunity occurs when B cells and T cells are activated by a pathogen, resulting in memory cells that can mount a strong secondary response if the pathogen is detected again. This is like training your body to recognize an invader so it knows exactly what to do when it sees one.

Naturally acquired active immunity happens as a result of surviving an infection and developing immunological memory. Artificially acquired active immunity, on the other hand, can be induced by vaccination, which stimulates a primary response against an antigen without causing symptoms of the disease.

Vaccines: The Modern Arsenal

There are four types of traditional vaccines:

• Inactivated vaccines composed of killed micro-organisms.
• Live, attenuated vaccines composed of weakened micro-organisms.
• Toxoids composed of inactivated toxic compounds.
• Subunit, recombinant, polysaccharide, and conjugate vaccines composed of small fragments or pieces from a pathogenic organism.

Newer types of vaccines include Outer Membrane Vesicle (OMV) vaccines containing the outer membrane of a bacterium and genetic vaccines delivering nucleic acid that codes for an antigen into host cells. These are like advanced weapons in your body’s arsenal, designed to fight off specific threats with precision.

Hybrid Immunity: The Future

Hybrid immunity is a combination of natural immunity and artificial immunity, which has been shown to be effective against SARS-CoV-2 variants. This approach combines the best of both worlds – the body’s innate defenses with the targeted responses provided by vaccines.

The Genetic Basis of Immunity

Immunity is determined genetically, with genomes encoding antibodies and immune response genes. There are many genes required for specific immune responses, such as Tumor Necrosis Factor (TNF), which is required for defense against tuberculosis. The condition is therefore called Mendelian susceptibility to mycobacterial disease (MSMD) and variants of it can be caused by other genes related to interferon production or signaling.

So, the next time you get a vaccine or passively receive antibodies from your mother’s milk, remember that these are just modern versions of ancient solutions. The journey of immunity is a fascinating one, filled with history and innovation. And as we continue to develop new vaccines and understand our immune systems better, we’re getting closer to a world where diseases are not just managed but conquered.