Immunity is the ability of body to fight against infections. immune organs are inside our body which provides the site of synthesis of immune cells.

1. ORGANS OF IMMUNE SYSTEM
NAME - ISHIKA MOHITE GUIDED BY - DR. CHAITALI NIRATKER
SEMESTER - V BATCH - 2021

2. Outline
o Introduction of immune organs
o Primary Lymphoid organs
o Secondary Lymphoid organs
o Interactions between immune organs
o Disorders of immune organs

3. Introduction to Immune Organs
• Immune organs play a crucial role in the
body's defense against pathogens.
• These organs are responsible for the
production, maturation, and activation of
immune cells.
• Immune system consists of two organs
– Primary Lymphoid organs and
Secondary Lymphoid organs.
• The major immune organs include the
bone marrow, thymus, lymph nodes,
spleen, and tonsils.

4. PRIMARY LYMPHOID ORGANS
• The primary lymphoid organs are those
organs where T-Lymphocytes and B-
Lymphocytes mature and acquire their
antigen specific receptor.
• Primary lymphoid organs consist of the
following organs:
1 Thymus Gland.
2 Bone Marrow.

5. Thymus
 Thymus is a primary lymphoid organ found in all
vertebrates.
 The thymus is responsible for the maturation of T
lymphocytes.
 T lymphocytes undergo selection and education
in the thymus, ensuring their ability to recognize
and respond to foreign antigens.

6. Thymus Education
• Prior entering the thymus T-cell precursor is lack antigen receptors TCR, CD4 and CD8
molecules on their surface .
• During passage through the cortex of the thymus they differentiate to T cell that
express TCR, CD4+ and CD8+ (Positive selection)
• In the medulla, these cells differentiate into express either CD4+ if contacts a cell
bearing class II MHC proteins or CD8+ if contact a cells bearing class I MHC proteins
(Negative selection)
• Negative & Positive selections are two processes eliminate immature T cells lacking
proper antigen receptor specificities.
• When T cell express the CD4 receptor become helper T cell while those express the
CD8 receptor become cytotoxic T cell.

7. Bone Marrow
 Bone marrow is the primary site for the production of blood cells, including immune cells.
 B lymphocytes are formed (originate) within the Bone marrow.
 It is a lymphocyte cell and derived its name from the site of maturation.
 After maturation, when they leave bone marrow, they express antigen binding receptor known a B-
cell receptor (BCR)
 At this stage this B-cell is known as naive B-cell, means do not previously encountered with
antigen, these B cells then migrate to secondary lymphatic organs, such as the spleen or lymph
nodes, where they wait to encounter foreign antigen.
 Binding of the antigen to BCR cause the B-cell to divide rapidly and produced two types of B-cell
 (1) Memory B cell (2) Plasma cell or effector B-cell

9. SECONDARY LYMPHOID ORGANS
 The secondary lymphoid organs are specially
evolved to be sites within the body where
naïve immune cells have the maximum
possibility of meeting and responding to
antigen.
 They consist of :
I. Spleen.
II. Lymph nodes.
III. Mucosa- associated lymphoid tissue.

10. Spleen
 The spleen is the largest lymphoid organ in the body.
 It filters blood and removes old or damaged red blood cells.
 The spleen also plays a crucial role in immune responses by trapping and
destroying pathogens.
 It is located on the left side of the body just above the kidney.
 It is enclosed by a capsule and divided by trabecula into communicable
compartments.
 It is composed of white pulp, rich in lymphoid cells and Red pulp contains large
quantities of erythrocytes, macrophage and some lymphocytes.
 The spleen is also referred to as the graveyard of RBCs.
 It plays the dual role of removing aged or injured red blood cells in the red
pulp and producing antibodies in the white pulp

12. Lymph Nodes
 Lymph nodes are small, bean-shaped structures distributed throughout the body
 They filter lymph fluid, trapping foreign substances and activating immune responses.
 The lymph nodes are composed of medulla and cortex which surrounded by a capsule
of connective tissue.
 The cortical region contains primary lymphoid follicles, after antigenic stimulation
enlarge to form secondary follicles with germinal center rich with B cells.
 The paracortical area contains T cells and dendritic cells. Antigen presenting occurs in
this area that result in T cell activation
 The medullary area is rich with plasma cells.
 Lymph nodes have two primary functions:
 Filter out potentially harmful particles from the lymph & act with immune
surveillance provided by macrophages and lymphocytes.

14. MALT (Mucosa Associated Lymphoid Tissue)
 MALT is located within the lining of the major tracts (digestive, respiratory and urogenital)
system have a combined surface area and the major sites of entry of most pathogens.
 These vulnerable membrane surface are defended by a group of organized lymphoid
tissues known collectively as mucosal associated lymphoid tissue (MALT).
 Examples:
 Gut-associated lymphoid tissue (GALT),
 Bronchus-associated lymphoid tissue (BALT) • Conjunctiva-associated lymphoid tissue
(CALT).
 Skin -associated lymphoid tissue (SALT).

16. Interactions between Immune Organs
• Immune organs work together to
coordinate immune responses.
• For example, lymphocytes produced in
the bone marrow and thymus migrate to
lymph nodes for activation.
• The lymphatic system facilitates the
movement of immune cells between
different organs.

17. Disorders of Immune Organs
• Disorders affecting immune organs can lead to immune deficiencies or autoimmune
diseases.
• Examples of immune deficiencies include severe combined immunodeficiency
(SCID) and acquired immunodeficiency syndrome (AIDS).
• Autoimmune diseases, such as rheumatoid arthritis and systemic lupus
erythematosus, result from the immune system attacking healthy tissues.