1. Immunology Chapter 3, Lecture 4
Richard L. Myers, Ph.D.
Department of Biology
Southwest Missouri State
Temple Hall 227
Telephone:

2. Organs of the Immune System
Divided on the basis of function
primary lymphoid organs
secondary lymphoid organs
Primary (central) lymphoid organs
responsible for maturation of lymphocytes
bone marrow
thymus
Secondary lymphoid organs
trap antigens and allow lymphocytes to respond
other lymphoid tissue

4. Primary lymphoid organs
Thymus
cells entering the thymus are thymocytes
the thymus is a flat, bilobed organ with lobes divided in lobules separated by trabeculae
each lobule divided into inner (medulla) and outer (cortex) compartments
thymic hormones cause differentiation and maturation of T lymphocytes
a1-thymosin, b4 -thymosin, thymopoietin and thymulin

5. Primary lymphoid organs (cont)
Antigenic diversity of TCR results from random gene rearrangements in thymus
Most thymocyte progeny undergo programmed cell death by two-step selection process (99%)
Neonatal thymectomy results in decrease of circulating T cells and cell mediated immunity
DiGeorge’s syndrome in humans
nude mice have no thymus
Thymus reaches its maximal size at puberty
then atrophies
fat content increases
next slide shows a cross-section of the thymus

6. Thymus

7. Bone marrow Bone marrow
site of B cell maturation
maturation occurs in the “microenvironment”
stromal cells secrete involved cytokines
a selection process eliminates some B cells
The equivalent in birds is the bursa of Fabricius
The next slide shows the bone marrow

8. Bone marrow with adipose tissue

9. Lymphatic system Fluid component of blood is plasma
without clotting factors called serum
Plasma leaves the capillaries and moves into the interstitial tissues
some returns, the remainder is called lymph
This moves into the lymphatic vessels
Returns to the blood via the thoracic duct
Antigens move with lymph into lymphoid tissues

10. Secondary lymphoid organs
Before antigenic stimulation, resting B cells are organized into a primary follicle
After antigenic stimulation, the primary follicle become a larger secondary follicle
contains many proliferating B cells which comprise a germinal center
Lymph nodes and the spleen have these structures

11. Lymph nodes
Some lymphatic tissue is composed of diffuse collections of lymphocytes and macrophages
Others organized into lymphoid follicles
Contain lymphocytes, macrophages and dendritic cells in reticular network
Lymph nodes are divided into cortex, paracortex and medulla
Medullary plasma cells produce antibodies

12. Section of enlarged human lymph node (low power view) showing numerous enlarged lymphoid follicles, each composed of a mantle of dark stained small lymphocytes surrounding a pale stained germinal center.

13. Human lymph node showing two enlarged germinal centers containing IgG producing B cells (white) using fluorescent anti-human IgG.

14. Spleen Functions to filter blood and trap blood-borne antigens
Composed of red pulp (macrophages and red blood cells) and white pulp
White pulp surrounds the arteries and forms the PALS
Splenectomy predisposes to the individual to several bacterial diseases
The next slide shows a section of the spleen

15. Spleen

16. Assignment
Begin reading Chapter 4, Antigens
Study question 2 (pg 105)