• Immunity, first defined by Sir Mac Farlane Burnet, is
the body’s ability to destroy pathogens or other foreign
materials, and to prevent certain infectious diseases.
This ability is of vital importance because the body is
exposed to pathogens since birth.Immune system
• The human immune system comprises lymphoid
organs, tissue cells and soluble molecules such as
antibodies.
Lymphoid organs
• Lymphoid organs are those organs where the maturation
and proliferation of lymphocytes takes place.• Structurally and functionally diverse lymphoid organs
and tissues are interconnected by the blood vessels
and lymphatic vessels, through which lymphocytes
circulate.types of lymphoid organs
• There are two types of lymphoid organs : primary
lymphoid organs and secondary lymphoid organs.
• The primary lymphoid organs are those organs
where T-lymphocytes and B-lymphocytes mature and
acquire their antigen-specific receptors.
• Primary lymphoid organs include bone marrow and
thymus, while in birds it is called Bursa of Fabricius.
• After maturation, B-lymphocytes and T-lymphocytes
migrate via blood vascular and lymphatic system to
the secondary lymphoid organs.
• Here they undergo proliferation, differentiation, and
acquire immune response to antigens.
• The secondary lymphoid organs are lymph nodes,
spleen, tonsils, Peyer’s patches of the small
intestine, appendix and mucosal associated
lymphoid tissues (MALT).