Emberin
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#1
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Would someone please be able to explain how clonal selection works in humoral immunity? Thanks!
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kkboyk
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(Original post by Emberin)
Would someone please be able to explain how clonal selection works in humoral immunity? Thanks!
B cells express antigen-specific receptors before antigens (each B-cells are unique and specific to only one type of antigen) are ever encountered in the body. These B-cells roam, and their receptors bind to infected body cells or an antigen itself which causes it to activate. After B cell activation, the B cells clone themselves undergo clonal expansion, but during each cellular division, random mutations occur that gradually increase the binding affinity for B cell-produced antibodies to antigens.
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SANTR
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(Original post by Emberin)
Would someone please be able to explain how clonal selection works in humoral immunity? Thanks!
Humour meaning 'body fluid'. Involves the production of antibodies which circulate in the fluid. There are 2 types of white blood cells, lymphocytes and phagocytes. B lymphocytes (B cells) can take in, by endocytosis, e.g. bacterial cells, the B cells process the bacteria cells and present its antigens on the B cell's cell-surface membrane. T lyphocytes with complementary shaped receptors to the antigens, bind to the antigens to cause the B cells to divide by mitosis into a group of identical B cells. The group of B cells all produce the same antibodies. A bacteria cell doesn't only have one type of antigen, it has several different antigens and each antigen stimulates a different B cell (as each B cell is only specfic to a particular antigen), thus resulting in different clones of B cells and members of the same clone produce the same antbodies.
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Emberin
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I think I understand a bit more, but I'm still a bit confused. This is what the textbook says:

"Activated T helper cells bind to a B cell APC. This is clonal selection - the point at which the B cell with the correct antibodies to overcome an antigen is selected for cloning"

I still a bit confused because I thought an APC just presented the antigens, but didn't play a part in actually producing the antibodies?
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Abistudyhard
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The antigen presenting cell doesn't directly produce antibodies, it is cloned by mitosis to produce plasma cells and memory cells, it those plasma cells which secretebthe antibodies. The information about the structure from the antibody is passed on during mitosis into the plasma cells so they can produce antibodies with the right specific shape
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