I am confused about I antigens. My book states that most adults carry the I antigen. I know that it is a cold agglutinin so not clinically significant, but a little bit later down in the paragraph it says that most adults have anti-I if tested at 4C. Is this true and if so why? Does that mean that if we performed our tests at 4C that we would mostly always get a positive because of this antigen. I know that this antibody is often the cause of cold agglutinin disease. How could we tell if this is the case if most people carry this antigen and this antibody. Help is appreciated in advance. thank you

I am confused about I antigens. My book states that most adults carry the I antigen. I know that it is a cold agglutinin so not clinically significant, but a little bit later down in the paragraph it says that most adults have anti-I if tested at 4C. Is this true and if so why? Does that mean that if we performed our tests at 4C that we would mostly always get a positive because of this antigen. I know that this antibody is often the cause of cold agglutinin disease. How could we tell if this is the case if most people carry this antigen and this antibody. Help is appreciated in advance. thank you

Hi tuffgrrrrl,

Yes, what you have read is true, although it is often quite difficult to detect the auto-anti-I, even at 4oC by standard serological techniques.

Some individuals do, however, have an auto-anti-I that can quite easily be detected at 4oC by standard techniques and, indeed, in the pathological condition known as CHAD, the auto-anti-I will have a much wider thermal amplitude (and, usually, but not always, a very high titre), reacting up to, and sometimes above, 30oC.

It is possible that this natural "cold" auto-anti-I is produced by the immune system as a pseudo-alloantibody during the time that the infant is I-i+, when the I antigen is just developing, and appears as a "foreign" antigen to the immune system (not that the immune system is particularly great at that time of life!), and that the low-grade IgM auto-anti-I persists from this time onwards.

Of course, this form of auto-anti-I is not, as you say, clinically significant, as it is usually weak, and reacts only in the cold, whilst the body is at, give or take, 37oC.

I hope that explanation is of some little help.

:confuse::confuse:

Hi friends,

Take care, the CAD fix complement, so the direct antiglobulin test is positive (mostly C3d) and clinical of intravascular hemolysis.

The anti-I/i clinically not significative, the DAT is negative.

hope this may be ussefull

Thank you for your response it really helped me. Your response was so basic and well worded.