Kategorie B - Liegt zur Lizenzierung ohne Wasserzeichen in folgendem Format vor: 720x576. Die Einbettung mit Wasserzeichen ist kostenlos. English:Category B - full version without watermark 720x576 (check terms and conditions at ) The embed version with watermark is free of charge. Description: When a macrophage has eaten an invader, it presents an antigen fragment from the invader on its own surface, a process called antigen presentation. When the receptor of a helper T cell recognizes the antigen, the T cell is activated. Once activated, helper T cells start to divide and to produce proteins that activate B and T-killer cells. The killer T cell is specialized in attacking cells of the body infected by viruses and sometimes also by bacteria. The B lymphocyte cell searches for antigen matching its receptors. The second time an intruder tries to invade the body, B and T memory cells help the immune system to activate much faster.
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