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