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LYMPHOID ORGNS
Function
- maturation
- differentiation
- proliferation
Primary (central) L.O.
T and B startto express
Ag - specific receptors
Secondary (peripheral) L.O.
Ly proliferation and differentiation after
interaction with Ag
Primary (central) L.O.
1) Thymus
2) Bone marrow
Thymus 1
Morphology: lobular organ 
cortex
medulla
Function: maturation of T cells (only 1 x 106 of 5 x 107 tymocytov mature)
Maturation:
 3 STEPS:
1) Migration and proliferation
2) Differentiation
3) Selection
1) Migration and proliferation
Thymocytes react with epithelial cells (cortex), dendritic cells
and Mph (medulla)
2) Differentiation
1) step - 3 negat. thymocytes (CD3-,CD4-,CD8-)
markers CD44+,CD25+,CD117+
TCR genes not rearranged
2) step - differentiation - TCR 
TCR γ
markers CD44-, CD25+, CD117+
3) thymocytes TCR γ   T Ly (CD3+, CD4-, CD8-)
5% of matured T cells
thymocytes TCR   Th (CD3+, CD4+, CD8-)
Tc (CD3+, CD4-, CD8+)
THYMUS
2
POSITIVE SELECTION
Only thymocytes with affinity to „self“-MHC + Ag survive
AIM: Elimination of nonfunctional T cells
MHC + epitop-Ag
TCR/CD3
THYMUS
3
NEGATIVE SELECTION
Thymocytes with high affinity to MHC + self Ag
are eliminated - clonal deletion
or inactivated – clonal anergy
AIM: Elimination of AUTOREACTIVE T cells
Secondary lymphoid organs
Functions
1. Trapping and concntration of Ag
2. Production of Ab and Ag specific T cells
Secondary lymphoid organs:
1. Spleen - blood born microbs and Ag
2. Lymph nodes - lymphatic pathway > skin, mucosa
3. Mucosa associated lymphatic tissue (MALT) – lining of mucosa surface
Ag invading mucosa
SPLEEN
Function - Ab synthesis and releasing to circulation
- hemokaterhesis / Tr a Er
(
Structure:
red pulp
white pulp
SLEZINA
Red pulp
plazma cells, Ma, Er, Tr, PMNL and Ly.
White pulp (PeriArteriolar Lymphoid Sheath - PALS).
T cells round central arteria
B cells in
primary folicules ( non stimulated)
secondary folicules (Ag stimulated)
germinal centre / memory cells
B Ly represent 50% spleen cells, 30-40% - T Ly.
Lymph node
(LN)
Structure - cortx
- medulla
Cortex
Primary folicules – non activated B cells
Secondary folicules - response to Ag
- Activated B cels – differentiation to plasma cells
- Th support B cell differentiation
- dendritic cells – Ag presentation
- FDC - activation of memory cells
- Mph
Interfolicular space and in paracortex – T cells (mainly Th)
Medulla
Ly, high number of Mph and dendritic cells
Lymph node
(LN)
Ag enters LN and trapped by Mph and dendritic cells
Degradation of Ag . Fragments (epitopes) are expressed on the
surface of APC cells together with MHC molecules
Activation of T cells
The first mitotic wave in T zones is recorded 1-2 days after
contact with Ag
 prolif. of B Ly, germinal centrers
Immune system of mucosa - MALT
>50% of lymphoid tissue
- (GALT) gut-associated lymphoid tissues
- (BALT) bronchus-associated lymphoid tissue
-(GUALT) genitourinary-associated lymphoid tissue
Exmples of MALT: tonsiles, appendix, Peyer`s patches, etc. …
Mucosa associated lymphatic tissue - MALT
Structure of MALT
1. Organized MALT (o-MALT) – immune cells in
epithelial layer of mucosa and under epithelium
Induction of immune reaction
2. Diffuse MALT (d-MALT) – various types of lymphoid cells
(B and T Ly, Ma, Ne, Eo, Ma) in lamina propria
Effector phase of immune reactions
Organized MALT (o- MALT)
Peyer`s patches :
1. Lymphoid folicules (> 100)
central part - B Ly, FDC, DC, Ma
peripheral part - T Ly
2. Epithelium
- „M“ cells – transport of Ag
- intra epithelia T Ly – 80% belong to CD8+ (regulatory function)