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Humoral or antibody-mediated immunity involves production of antibodies against foreign antigens. Antibodies are produced by a subset of lymphocytes called B cells. B cells that are stimulated will actively secrete antibodies and are called plasma cells. Antibodies have a role in defending against bacteria, bacterial toxins, and viruses that circulate freely in body fluids, before they enter cells. Also, antibodies cause certain reactions against transplanted tissue.

Cell mediated immunity involves specialized set of lymphocytes called T cells that recognize foreign antigens on the surface of cells, organisms, or tissues. T cells regulate proliferation and activity of other cells of the immune system: B cells, macrophages, neutrophils, etc… They defend against bacteria and viruses that are inside host cells and are inaccessible to antibodies, cancer cells, transplanted tissue, fungi, protozoa, and helminthes.

Questions ( Click “comments” and type your answers):

1. How is the antibody molecule presented?

Aya: It has two sides able to fix 2 antigens of the same type.

Sara: presented by two sides that attracts antigens to it.

2. Can a lymphocyte B recognize several antigens? Explain.

Aya: No, because it can recognizes only a specific antigen that are linked to it.
Sara: no it can not. It can only recognize the antigen it is linked to it.

3. How does a lymphocyte T identify the antigen?


Aya: It identifies the antigen only when it is displayed on the surface of the infected cell membrane.
Sara: it identifies the infected cell membrane antigen.

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