C3.2.7 Antigens as recognition molecules that trigger antibody production Notes

Antigens as Recognition Molecules That Trigger Antibody Production

1. Imagine your body as a well-guarded fortress.
2. To keep invaders out, it relies on a sophisticated system of recognition and defense.
3. At the heart of this system are antigens are molecules that act as "name tags" for foreign invaders, alerting your immune system to take action.

What Are Antigens?

1. Structure: Most antigens are glycoproteins (proteins with attached sugar molecules) or other proteins.
2. Location: They are typically found on the outer surfaces of pathogens, such as bacteria, viruses, and fungi.

How Do Antigens Trigger Antibody Production?

1. Recognition of Non-Self: The immune system uses antigens to distinguish between self (your body’s cells) and non-self (foreign invaders).
2. Activation of Lymphocytes:
   1. Helper T-Cells: Recognize antigens presented by macrophages and activate B-cells.
   2. B-Cells: Produce antibodies specific to the antigen.

Step-by-Step Process of Antibody Production

Antigen Recognition

1. Antigens on the surface of a pathogen are recognized by specific B-lymphocytes.
2. Each B cell has receptors on its surface that can bind to a specific antigen, which acts like a key fitting into a lock.

Activation of B-Lymphocytes:

1. The binding of the antigen to the receptor on a B cell triggers the activation of that B cell.
2. The activated B cell then undergoes clonal selection, where it divides rapidly to produce a clone of identical B cells.

Differentiation into Plasma Cells:

1. Some of the activated B cells differentiate into plasma cells, which are responsible for producing antibodies.
2. Plasma cells are highly specialized for antibody production and secrete large quantities of antibodies into the bloodstream.

Antibody Production

1. The antibodies produced by plasma cells are specific to the antigen that triggered the immune response.
2. These antibodies are Y-shaped proteins that can bind to the antigens on the surface of the pathogen, marking them for destruction or neutralization.

Antigens on Erythrocytes and Blood Transfusions

1. Antigens can also be found on the surfaces of erythrocytes (red blood cells).
2. These antigens can stimulate antibody production if transfused into a person with a different blood group, which is the basis of blood group incompatibility.
   1. Blood Group Antigens: Red blood cells (erythrocytes) have specific antigens on their surface, such as A, B, or Rh.
   2. Immune Response: If blood with different antigens is transfused, the recipient’s immune system may recognize these antigens as foreign and produce antibodies against them.

Why Are Antigens Important?

1. Immune Defense: They enable the immune system to identify and target pathogens.
2. Vaccination: Vaccines introduce harmless forms of antigens to "train" the immune system, preparing it for future infections.
3. Medical Applications: Antigens are used in diagnostic tests, such as pregnancy tests and COVID-19 rapid tests.