Page 77 - Textbook of Pathology, 6th Edition

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Immunopathology
Chapter 4
Chapter 4
Including Amyloidosis CHAPTER 4

Natural or innate immunity is non-specific and is
INTRODUCTION
considered as the first line of defense without antigenic
Immunity and immunopathology are proverbial two edges specificity. It has 2 major components:
of ‘double-edged sword’. a) Humoral: comprised by complement.
Before discussing immunopathology which is the study b) Cellular: consists of neutrophils, macrophages, and
of derangements in the immune system, it is important to natural killer (NK) cells.
know the normal structure and function of the immune Specific or adaptive immunity is specific and is
system (immunophysiology) and to get familiarised with a characterised by antigenic specificity. It too has 2 main
few terms and definitions commonly used in any description components:
of immunology. a) Humoral: consisting of antibodies formed by B cells.
An antigen (Ag) is defined as a substance, usually protein b) Cellular: mediated by T cells.
in nature, which when introduced into the tissues stimulates The various components of both types of immunity are Immunopathology Including Amyloidosis
antibody production. interdependent and interlinked for their functions.
Hapten is a non-protein substance which has no antigenic
properties, but on combining with a protein can form a new STRUCTURE OF IMMUNE SYSTEM
antigen capable of forming antibodies.
ORGANS OF IMMUNE SYSTEM
An antibody (Ab) is a protein substance produced as a
result of antigenic stimulation. Circulating antibodies are Although functioning as a system, the organs of immune
immunoglobulins (Igs) of which there are 5 classes: IgG, IgA, system are distributed at different places in the body. These
IgM, IgE and IgD. are as under:
An antigen may induce specifically sensitised cells a) Primary lymphoid organs:
having the capacity to recognise, react and neutralise the i) Thymus
injurious agent or organisms. ii) Bone marrow
The antigen may combine with antibody to form antigen- b) Secondary lymphoid organs:
antibody complex. The reaction of Ag with Ab in vitro may i) Lymph nodes
be primary or secondary phenomena; the secondary reaction ii) Spleen
induces a number of processes. In vivo, the Ag-Ab reaction iii) MALT (Mucosa-Associated Lymphoid Tissue located in
may cause tissue damage (Fig. 4.1). the respiratory tract and GIT).
These organs have been described in the respective
TYPES OF IMMUNITY. Broadly speaking, immunity or chapters in the book.
body defense mechanism is divided into 2 types, each with
humoral and cellular components: CELLS OF IMMUNE SYSTEM
The cells comprising immune system are as follows:
i) Lymphocytes
ii) Monocytes and macrophages
iii) Mast cells and basophils
iv) Neutrophils
v) Eosinophils
While morphologic aspects of these cells are covered
elsewhere in the book, their immune functions are briefly
considered below and summarised in Table 4.1.

Lymphocytes
Lymphocyte is the master of human immune system.
Morphologically, lymphocytes appear as a homogeneous
group but functionally two major lymphocyte populations,
T and B lymphocytes are identified; while a third type, NK
(natural killer) cells, comprises a small percentage of
Figure 4.1 Antigen-antibody reactions. Primary and secondary
reactions occur in vitro while tissue damage results from in vivo Ag-Ab circulating lymphocytes having the distinct appearance of
reaction. large granular lymphocytes.