Do you mean antibodies? Antibodies are the proteins that mark antigens (foreign material) as non self and tag it for destruction.

Everyone has a different library of antibodies/immunoglobulins. If you are comparing two people, one may have antibodies to antigens the other does not have (think vaccinated vs non vaccinated unexposed.) The two may also have structurally distinct antibodies but target the same antigen (like two people who get the same illness and develop an immune response and recover. There are also some antibodies that are the same between people, (like between a mother and neonate with antibodies that cross the placenta or are carried in breast milk.)

That’s my simplest explanation.

An antigen is just a word for something your immune system recognizes, like pieces of virus or bacteria, to help it determine what is foreign and needs to be killed/removed. So no, we often have very different antigens in our bodies, since we don’t all have the same viruses or bacteria in our bodies.

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Sorry I realise I forgot to add an important bit. Do we all have the same self antigens?

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No, we do not all have the same self-antigens. Self-antigens are proteins or other molecules that are present on the surface of our cells and are recognized as being "self" by the immune system. These self-antigens are typically unique to an individual and are used by the immune system to distinguish the body's own cells from foreign cells.

Self-antigens can include proteins such as major histocompatibility complex (MHC) molecules, which are present on the surface of almost all cells and play a critical role in the immune system's ability to recognize and attack foreign invaders. MHC molecules are highly variable and are thought to have evolved to provide a diverse range of self-antigens that can be recognized by the immune system.

In addition to MHC molecules, other self-antigens may include proteins and molecules on the surface of cells, such as cell surface receptors and enzymes. These self-antigens are also unique to an individual and help the immune system to recognize and distinguish the body's own cells from foreign cells.

If that's the case then at least do we have highly similar self antigens? Otherwise how would autoantibody tests work, there must be common ones. Or am I missing more of the picture? Are epitopes unqiue as well? I assume so if antigens are

Yes, humans have highly similar self-antigens, but there is still some variation between individuals. This is why autoantibody tests are not always completely accurate and may require further testing to confirm a diagnosis.

Epitopes are the specific parts of an antigen that are recognized by the immune system, and they can be either unique or shared between different antigens. In the case of self-antigens, the epitopes are typically highly conserved, meaning that they are similar among individuals. However, there can still be some variation in the epitopes, which can affect the immune system's ability to recognize self-antigens and may contribute to the development of autoimmune disorders.

Damn complexity. Thank you for the information, exactly what I'm looking for for but wasn't what I expected.

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Also antigen-specific antibodies, how come some stay and how come some go?

Antigen-specific antibodies are produced by the immune system in response to the presence of a specific antigen, such as a virus or bacteria. The production of antibodies is a natural process that helps the body to defend itself against infection and disease. Some of the antibodies produced in response to an antigen will remain in the body for a long time, providing ongoing protection against future exposures to the same antigen. Other antibodies may not persist for as long and may be cleared from the body over time. The length of time that an antibody remains in the body can depend on a variety of factors, including the specific characteristics of the antigen and the immune system of the individual.

Wait 1 more implication then, could that explain the reason for some people being seronegative for autoimmunity?

But it’s so interesting that some go and some stay. Is it because our cells can only hold so much “data”?

Correct. The reason for some people being seronegative for autoimmunity can be due to the variation in epitopes, or the specific parts of an antigen that are recognized by the immune system. If the immune system does not recognize the specific epitopes on a self-antigen, it may not produce antibodies against it, resulting in a negative test result. Additionally, the presence of autoantibodies does not always indicate the presence of an autoimmune disorder. Some individuals may produce autoantibodies as a result of normal immune system function, and they may not develop any clinical symptoms. Therefore, it is often necessary to confirm a diagnosis of an autoimmune disorder through other means, such as a thorough medical history, physical examination, and additional testing.

Very interesting. Thank you for the knowledge once again

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Thanks for all the assist on answering these questions! I was not fully committed to breaking down MHC proteins and how antibodies are made. Immunology isn’t my biomedical subject specialty.

I think SimShade made a beautiful recap but there is something that may be useful to add. I am an MD but not an immunologist so someone could sure be more accurate. It is true that there may be some variability in our self molecules/proteins/antigens (due to SNPs and other reasons). However the main parts (those with an active function such as enzymatic activity, receptor function etc) are usually conserved among individuals and sometimes among species. A lot of variability is found in the MHC molecules that have a key role in antigen recognition and presentation. This can explain in part why autoimmune disease develop more frequently in some individuals and the association with the HLA aplotype. Moreover, often when autoantibodies develop against some self-antigens (ex. anti-insulin antobodies or anti-TPO antibodies etc) there are different antibodies against different epitopes of the same molecule (polyclonal response). This is probably one of the main reasons why the tests for autoimmunity are quite accurate (because we usually don’t test for epitope specific antibodies even if it can be done using some specific tests). I hope this helps but a very useful test is: “Cellular and Molecular Immunology” by Abbas et al.

You gave me information I didn't even know I wanted:thank you!

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