What is Antibody M?

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  • Written By: M. Marquardt
  • Edited By: A. Joseph
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  • Last Modified Date: 13 November 2019
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Antibody M is another name for immunoglobulin M (IgM). It is an antibody found in B cells, one of the cells that play a large role in the human immune system. When a foreign body, or antigen, infiltrates the body, antibody M is the first antibody to appear.

Antibodies help the immune system identify possible dangers, such as bacteria or viruses. Though most antibodies have a similar base structure, each type has a distinct formation of amino acids at its tip. The unique tip configuration matches a similar formation of a specific antigen. If an antibody locks with its specific antigen, the body is alerted to the presence of a foreign body, prompting the immune system to move into action.

Antibody M is useful in medicine because it can bind to many different antigens, even those of a disease that has never before appeared in the body. Typically, ait appears during the initial stage of almost every infection. Doctors can take samples of a patient’s blood to test for this substance, therefore confirming an infection even if other symptoms are not present.


Another interesting property of antibody M is that it cannot cross the wall of a human placenta. This trait is useful for doctors monitoring the growth of a fetus in the womb or a baby after it is born. If a sample of fluid from the womb is found positive for this antibody, it implies that the fetus has an infection. Being able to know the condition of a baby before birth is key to a healthy labor and delivery.

When there is too much antibody M circulating in the body, it is known as hyper IgM syndrome. It is a rare genetic condition that can severely impair the immune system. When a person has the syndrome, his or her body produces too many copies of antibody M, many of which are of poor quality. The antibodies are not functioning properly, so that person is more susceptible to infection as well as autoimmune disorders. The syndrome also might make the person more likely to develop cancer at an early age.

Research into antibodies began in 1890, but it took nearly 100 years for specific antibodies to be identified. During the 1960s, antibody M was one of the first distinguished as unique, along with antibody G. In 1972, Rodney Porter and Gerald Edelman were awarded the Nobel Prize in Physiology or Medicine for their work discovering the chemical structure of antibodies.


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Post 7

I have just been in hospital and been told to carry a card showing I have the Anti-M in my blood. This is for information if I need a blood transfusion. I am not pregnant and not likely to be at my age, but was quite alarmed when this arrived on my door mat. What does this mean for me?

Post 6

I am about to give birth to my fourth child with my other children being ages 1, 2,and 3. None of my OB/GYNs ever told me I had Antigen M until two days ago during my 30 week check-up. I've never heard of this so naturally I had to look it up and I am so shocked. My three year old has cancer (T-Cell ALL) and I can't help but wonder if this has something to do with it?

Post 5

I have had two healthy children and I have this antibody. I developed it in a rare case where my partner is rhesus negative but I am positive and our two children are both negative as well. It would seem that I am now suffering from IgM syndrome.

Post 4

I am 11 weeks pregnant and found out that I have M-antigens. My OB doc wanted my husband to be tested,and his test came back positive as well.

My doctor has ordered no other tests to be done until I have my 18 week ultrasound done, and to see what that shows. I have done all kinds of research online and have found horror stories of this antibody and the things it a can do to my baby.

I've been monitoring the baby's heartbeat almost every day and it had been in the 170-178 range and the couple of ultrasounds I have had done, the baby looks good. Hopefully everything continues to go well. I'm scared but am trying to think positive.

Post 3

@epiphany5 - Thank you for posting this article. I am pregnant and my doctor just told me that I might have traces of antibody M in my body. I am still waiting on more test results to determine if these antibodies are actually present.

I was first made aware of these possible antibodies about a week ago. Since then, I have been doing a lot of online research on antibody M. I had no idea what it was before my doctor brought it up to me.

I have found out that a lot of women experience having these antibodies in their system while pregnant. Most testimonials I have read from pregnant women said that their doctors monitored the growth of their babies more closely because these antibodies were found.

All of the women said that their babies were born healthy, so I figured that I should have nothing to worry about. Reading your story further eases my mind.

Post 2

This is a really thorough article. I am currently an undergrad studying the human immune system in my anatomy classes. The information you wrote about matches perfectly with what my professor has lectured.

My professor has done an extensive amount of research on antibodies, including antibody M. In class, he used to call antibody M the smartest antibody of them all. He compared them to bulldogs, protecting the body from unwanted invaders. I always thought that this comparison was an accurate one.

One reason he called antibody M smart is because of how it forces the body to react to a bad blood transfusion. When a patient undergoes a transfusion that does not match well with their body

, antibody M forces the red blood cells to clump together. When doctors detect these clumps, they can assume that the blood from the transfusion is not compatible with the patient's system.

It is amazing how intelligent the human body can be. I love sharing my amazement with others!

Post 1

You certainly learn a lot about the human body when you are pregnant, or at least I did! I just gave birth to a healthy baby girl. I know all too much about the changes a woman's body goes through when she is carrying a child.

During my pregnancy, the doctor extracted fluid from my belly every time I went in for a checkup. One time, the doctor informed me that my baby's placenta might have an infection in it. He said that tests showed traces of Antibody M, which apparently would normally not show up in the placenta. He gave me some antibiotics to heal the infection, and my baby and I turned out fine.

I really

did not understand why the presence of Antibody M in my baby's water sack meant that she had an infection in there. My doctor tried to explain it to me, but I was confused. Reading this article has definitely helped me to understand. Thanks for writing it.

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