Page 152 - MNU microbiology theoritical 2025

General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025

III. Types of antigens

A. T-independent antigens

-T-independent antigens are antigens which can directly stimulate the B cells to

produce antibody without the requirement for T cell help

- In general, polysaccharides are T-independent antigens.

B.T-dependent antigens

T-dependent antigens are those that do not directly stimulate the production of

antibody without the help of T cells.

-Proteins are T-dependent antigens.

-Structurally these antigens are characterized by a few copies of many different

antigenic determinants

IV. Superantigens

• a class of antigens that result in excessive activation of the immune system.

Specifically, they cause non-specific activation of T-cells resulting in massive
cytokine release.

• Compared to a normal antigen-induced T-cell response where .001-.0001% of

the body’s T-cells are activated, SAgs are capable of activating up to 20% of

the body’s T-cells. This causes a massive immune response which is useless.

• Large amounts of cytokines (the most important of which is TNF-alpha) can

cause severe and life-threatening symptoms, including shock and multiple organ

failure.

• Examples of superantigens include:

1- Staphylococcal enterotoxins (food poisoning)

2- Staphylococcal toxic shock toxin (toxic shock syndrome)

General Microbiology & Immunology (PM 401) theoretical handbook Page 141