0:00:01.161,0:00:03.361
Antibodies are proteins that play an

0:00:03.474,0:00:05.824
integral role in the complex system of

0:00:05.983,0:00:08.293
specific immunity. They bind to and

0:00:08.571,0:00:10.681
inactivate foreign proteins called

0:00:10.939,0:00:13.429
antigens. Each type of antibody binds to

0:00:13.570,0:00:17.480
one kind of antigen molecule. B-cells are

0:00:17.617,0:00:19.797
one of the two types of white blood

0:00:19.872,0:00:23.872
cells that make antibodies. When a

0:00:24.221,0:00:27.101
bacterial cell enters the bloodstream,

0:00:27.160,0:00:29.800
proteins on its surface act as antigens

0:00:29.890,0:00:32.260
and trigger a response by the immune

0:00:32.397,0:00:34.877
system. These antigens will bind to the

0:00:34.929,0:00:36.729
unique B cells that have the

0:00:36.820,0:00:38.980
corresponding antibodies on their

0:00:39.067,0:00:41.247
surfaces. These B cells now divide.

0:00:44.124,0:00:46.724
Some continue to divide producing many

0:00:46.884,0:00:50.030
plasma cells. Plasma cells secrete large

0:00:50.069,0:00:52.309
quantities of antibodies into the

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bloodstream. This division of only the

0:00:54.785,0:00:58.085
appropriate B cells is called clonal

0:00:58.085,0:00:59.130
selection.