T Cell at Work

2 important questions on T Cell at Work

How can B7 bind with CD28 in virgin T cells if the affinity of CTLA-4 is much higher?

B7 can bind with CD28 in virgin T cells, because then there is much more CD28 relative to CTLA-4, which is not present. Experienced T cells start expressing more CTLS-4, so the B7 which first bound to CD28, now binds to CTLA-4.

Although IgA is an antibody, which can bind with pathogen. Why does the immune system not become activated?

The Fc part of IgA does not bind with Fc receptors of immune cells. Therefore, the immune system does not become activated.

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