Explain why an Rh-negative person does not have a transfusion reaction on the first exposure?

Explain why an Rh-negative person does not have a transfusion reaction on the first exposure to Rh-positive blood but does have a reaction on the second exposure. What happens when an ABO blood type is mismatched for the first time?
Answer:
We have some imune cells in our body called Memory cells( like memory B cells and Tcells)
when somebody is Rh+ it means he has the Rh antigene and when somebody is - means he don't.
on the first transfusion when a blood with Rh antigene to a person that doesn't have this kind af antigene the imune system respond but in a mild way. it produces antibodies and this Abs attach to the surface of memory cells, but we dont have acute responce because the antibody rate in our blood is not very high. on the second transfution the cells react fast and strong and the symptoms appear! :) hope it is enough!

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An Rh negative person does not have the D Ag on the RBC. Also the plasma lacks Ab against the Ag. On first exposure to Rh + blood the immune system is stimulated to produce Ab against the D Ag and memory cells are stored. On second exposure the memeory cells start producing the Ab rapidly without any latent period. Now is when we get transfusion reactions. When Abo blood is mismatched for the first time, we do have the Ab in the plasma i.e., Ag A on the RBC, Ab B in the plasma %26 so on. So immediate transfusion reactions occur- clumping of RBCs, blocking of capillaries, pain %26 tightening in the chest.

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Antibodies against the D antigen are not naturally occurring.
We call these "unexpected antibodies". The only way to develop an Anti-D is to be exposed to this antigen. Therefore, the immune system cannot react until the second and subsequent exposures. Because of bacteria with very similar antigens on their cell surfaces, people that lack A and/or B antigens naturally form antibodies against them. We call these "expected antibodies", and mismatching even the first time can be deadly.

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