Page 146 - MNU microbiology theoritical 2025

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

Fc region of the molecule is digested into small peptides by pepsin. The F(ab')2

binds antigen but it does not mediate the effector functions of antibodies.

Structure and some properties of IG classes

1- IgM
e) IgM

1. Structure IgM normally exists as a pentamer

- Its large size normally prevents it from crossing from

the bloodstream into tissues, so its role is primarily to

control bloodstream infections.

2. Properties

a) the 3rd most common serum Ig.

b) First antibody class produced during the primary

immune response.

c) Binding IgM to antigen leads to activation of the complement system (classical

pathway).

d) Provides direct protection by

- neutralizing viruses and toxins

- immobilizing motile organisms,

- agglutinating/precipitating antigens.

General Microbiology & Immunology (PM 401) theoretical handbook Page 135