An antibody is a protein made by the immune system.ย  When the body senses something foreign inside it (usually a germ), many parts of the immune system begin to act against it.ย  One part processes it, learns to recognize it, makes antibodies to capture it, & also remembers it.ย  That’s our immune recall, so the next time the same germ enters, the immune system can make thousands of antibodies immediately, to stop it on the spot.

Natural immunity occurs when a germ enters us.  Artificial immunity is the same immune system response, but to a vaccine, which uses either a part of a dead germ, or very weak live one.  Since actual germs provide a stronger stimulus than a vaccine, we may need ongoing booster shots so our immune recall can keep remembering it.

We use antibodies a lot in blood tests, to diagnose diseases.  Sometimes there’s just one test for a condition, but there may be two or three.  And tests may mean something different for different diseases.  For example:

1.ย  Rubella (“German Measles”).ย  A virus that causes serious birth defects during pregnancy.ย  We test all pregnant women for it.ย  If it’s “positive” (or “reactive”), it means they’re immune, usually because they were vaccinated with “MMR,” though immigrants from poor countries may be immune from having had the actual disease.ย  But if a pregnant woman has a fever and rash, we see if the antibody found is mainly the IgG type (meaning immune) or the IgM (meaning current infection, which would be real bad, but now seems eliminated in the U.S.).

Other diseases where IgG antibody means immune, & IgM means current infection, include Measles, Hepatitis A, Varicella, West Nile, and many other viruses.  For bacteria like Lyme Disease, IgG means previously infected, but the antibody doesn’t protect you from getting it again.

2.  HIV.  Here there’s no IgG or IgM, just one antibody.  If it’s positive, it means somebody passed the virus to you.  But the antibody isn’t strong enough to destroy the virus, so if your HIV antibody test is positive, you have HIV infection.

3.ย  Hepatitis C.ย  Also no IgG or IgM here, so a positive result means you were passed the virus.ย  But about 20% of people get cured by themselves, which has to be determined by a PCR test for viral load (if negative, or “undetectable,” then you’re cured).

4.ย  Covid-19.ย  IgM and IgG both turn positive about 3-4 weeks after getting infected, weโ€™re not sure how long they last. ย They donโ€™t mean at all that youโ€™re immune or protected.ย  Thereโ€™s rarely a good reason for an individual to get tested (Covid tests by PCR are extremely important).

Then there are antibody tests to diagnose a variety of auto-immune diseases, when the body attacks itself.ย  But lots of people test positive who may never get the disease.ย  So we only order those antibody tests if a patient has signs and symptoms of the illness we’re looking for.

In certain cases, antibodies can be manufactured, and injected into people.  Usually it’s done as an attempt to treat or cure a disease.  Sometimes it’s done for prevention.

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