rev: August 5, 2004
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The following book on the IgG Subclass is made available by the permisssion
of CLB Reagents (Netherlands). It is for your personal use and may not be
reproduced without the permission of CLB Reagents. This material is for
information use only and should not be construed as medical advice. We are
not responsible for any misprints or error or ommissions. Certain charts
,graphs and table have been ommitted or changed in style (not content)
to fit this web site. Please use this information as part of your discussion
with your medical professional.
1 The immune system in a nutshell
The immune system consists of two functional components: the innate and the adaptive immune system. The innate immune system prevents penetration and spread of many infectious agents by means of a variety of physical, biochemical and cellular barriers (skin,mucosa,lysozyme,complement,phagocytes). Apart from these first lines of defence, the adaptive immune system may be called upon to react against and clear the harmful agent. Furthermore, after the first attack, the adaptive immune system develops a specific immunological memory, leading to a stronger, faster and more effective response upon renewed contact with the same agent. The adaptive immune system consists of a variety of cells and molecules, among which lymphocytes and immunoglobulins are the key elements. There are two types of lymphocytes, T cells and B Cells. T cells play a pivotal role in regulating the immune response and are also responsible for cellular immunity, while B cells are essential in the effector phase of humoral immunity. After exposure to antigen and mostly with the help of T cells,B cells can differentiate into plasma cells which synthesize molecules (antibodies or immunoglobulins) that can react with the antigen(1,2).
Immunoglobulins are a group of closely related glycoproteins composed of
82-96% protein and 4-18% carbohydrate. The basic immunoglobulin molecule
has a four-chain structure, comprising two identical heavy (H) chains and
two identical light (L) chains, linked together by inter-chain disulfide
bonds. Intra-chain disulfide bonds are responsible for the formation of
loops,leading to the compact,domain-like structure of the molecule. The
aminoterminal portions of the heavy and light chains,characterized by a highly
variable amino-acid composition, are referred to a V H and V L, respectively.
The constant parts of the light chain are designated as C L, while the constant
parts of the heavy chains are further divided into three distinct subunits:
C H1,C H2 and C H3 (figure 2). Functionally, the V regions are involved in
antigen binding. The C regions interact to hold the molecule together and
are involved in several biological activities, the so-called effector functions
such as complement binding, placental passage and binding to cell
membranes.
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