Corona Daily 344: The Soldiers within Us

Two weeks ago, during my morning walk; I met V. and M., a young couple, good friends of mine. Hadn’t seen them for a few weeks. Walking without a mask, they looked cheerful. V and his family had been down with Covid-19 for a few days. All nine family members, including two young daughters, had now taken antibody tests. All tests were positive, the source of their joy.

“Antibody tests are more reliable,” V. said, “because they are blood tests, not swab tests. Now that all of us are positive, we are immune. Widespread antibody tests will allow people to resume their work. You test positive, and you start a normal life.”

Curious, I began researching antibodies and Covid-19 antibody tests. As someone with no medical education, I am not qualified to write on the subject. However, in coronavirus times, you will notice that nobody is an expert (or everybody is an expert). The novel coronavirus retains its novelty, and the scientific world continues to update facts and opinions.

Today and tomorrow, I aim to reproduce some stuff in simple-to-understand language. For a start, I recommend the paper “Understanding Antibody Testing for Covid-19” by the Jacofskys, a family of doctors. For those short of time, I give its précis here.

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When a foreign substance such as a virus attacks us, our immune system produces protective proteins. They are called antibodies (or immunoglobulin). After an infection, the cells producing virus-specific antibodies multiply and increase proportionally. These are the newly recruited soldiers within us who will be alert to stop the virus from attacking us again. This feature is called “immunological memory”. Like a smart policeman recognizing a criminal from a previous crime, and stopping him from committing another. One exceptional quality of our immune system is its ability to remember previous infections. This ability is also the foundation of vaccinations.

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Each antibody recognizes a particular virus, a phenomenon known as “antibody specificity”. An antibody that recognizes the mumps virus can’t recognize the measles virus and the other way round. A virus has multiple binding sites. Like in a football field, where different players mark different opponents, multiple antibodies are required to recognize multiple binding sites of a virus. Only when two different, but very similar, viruses have identical structures will cross-reactivity occur. (The hypothesis that Indians may be protected against Covid-19 by the BCG vaccines taken in childhood may not be true).

Immune memory is long-lasting. Measles infection memory in adults is so strong it would take 3000 years to decrease it by half. It is obvious humans can’t get measles two times.

Within an individual, the immune memory must be located throughout the body, to prevent attack from every side. Our blood does that job, by circulating antibodies. Natural killer (NK) cells within tissues remain “alert”, but not activated. They are ready to attack rapidly if reinfection occurs.

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Some infections are so powerful they can leave an impact beyond a generation. When an infection is lethal, individuals with genes that fight, resist and survive can transfer the immune memory to their children. Herd immunity in such a case is possible through natural selection, rather than vaccination or infection.

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The word “immunity” is understood differently by immunologists and lay people. For immunologists, immunity simply means the immune system has responded to a virus, for example by producing antibodies. Most others understand immunity as being protected from infection. Unfortunately, this colloquial use is not correct. Immunity depends on how effective, numerous and durable the antibodies are. More on that tomorrow.

Ravi