Lecture # 75
IMMUNITY – 1
Dr. Iram Sohail
Assistant Professor
Pathology
College Of Medicine
Majmaah University
OBJECTIVES
• Define & classify autoimmunity
• Explain immunological tolerance
• Discuss the mechanism of autoimmunity
Definition of autoimmunity
• It is the immune reaction to self-antigens.
• In autoimmunity, antibodies are formed
against body`s own antigens, like antibodies
against heart cell, joint cells, kidney cells.
Classification of autoimmunity
• Autoimmune disorders are classified into
1. Systemic autoimmune disorders
2. Organ specific autoimmune disorders
Autoimmune Diseases
Immunological tolerance
• It is the unresponsiveness to an antigen that is
induced by exposure of specific lymphocytes
to that antigen.
• Self-tolerance is the lack of immune
responsiveness to one`s own antigens.
• Tolerance is divided into 2 groups
1. Central tolerance
2. Peripheral tolerance
1. Central tolerance
• Deletion of self-reactive T & B lymphocytes
during their maturation in central lymphoid
organs
– T-cells in thymus
– B-cells in bone marrow
• This deletion done by apoptosis.
2. Peripheral tolerance
• Self-reactive T-cells those escape deletion in
thymus can be deleted in peripheral tissue
and this is called peripheral tolerance.
• Several mechanisms can cause peripheral
tolerance
Anergy
• Functional inactivation (rather than death) of
lymphocytes.
Suppression by regulatory T-cells
• Response of T-lymphocytes to self-antigens may
be suppressed by regulating T-cells.
Activation-induced cell death
• Apoptosis of mature lymphocytes as a result
of self- antigen recognition.
Mechanism of Autoimmunity
• Exact mechanism is not known
• Some mutations break down the normal
immunological tolerance and causes
autoimmunity.
• Autoimmunity can be related to
– Inheritance of some genes
– Infection
– Injury