3.3.1.2

Immunoglobulin/Antibodies

What are antibodies? As shown in Figure 3.7, antibodies are molecules made up of

two heavy chains (50 kDa each) and two light chains (25 kDa each) held together

by disulfide bonds. These molecules recognize an antigen with very high specificity.

Both heavy and light chains have variable and constant regions. The variable region

makes up the antigen binding site. The constant region of the antibody, also known

as the Fc domain, interacts with the rest of the immune system to bring about

effector function [5].

3.3.1.2.1

Heavy and Light Chain Isotypes

There are different kinds of both heavy (μ, δ, γ, α ε) and light chains (κ and λ), and

this gives rise to a diverse set of antibodies since each heavy chain isotype can

associate with either light chain isotype. This diversity in structure is also reflected

in distinct characteristics and functions. Relevant for this discussion are the IgG and

IgM antibody isotypes. The structures of these antibody types are shown in

Figure 3.8. The first antibody to appear in the circulation as a response to an in-

fection, is a pentameric molecule wherein all 10 heavy chains are of the type μ,

hence the name IgM. At this point the affinity of antibody recognition is not very

FIGURE 3.6 Lymph node. T- and B-cells are brought to lymph nodes by blood vessels.

This figure shows the steps involved in B-cell maturation upon binding soluble antigen that is

brought to the lymph node by lymph vessels. Following antigen-binding, B-cells migrate to

the follicles, the site of clonal expansion. Antigen-laden dendritic cells also enter the lymph

node and present their antigens to T-cells, thereby activating them. Activated T-cells can

enter the follicle where they stimulate B-cells towards maturation.

42

Bioprocessing of Viral Vaccines