Download Cells of the immune system

‫بسم هللا الرحمن الرحيم‬
Cells of the immune system
-monocytes/macrophages
-granulocytes/polymorphonuclear cells (PMN)
-mast cells
-interdigitating dendritic cells (DC)
-follicular dendritic cells
-Lymphocytes
NK cells
B cells
CD4+ and CD8+ T cells
Lymphoid System Basics
• Cells, tissues and organs that function to
protect body from invasion and damage by
foreign cells, microbes, viruses and parasites
• Also known as the immune system
• Two types of lymphoid tissues:
– Encapsulated: connective tissue capsule
• spleen, thymus, lymph nodes
– Unencapsulated (or partly encapsulated)
• tonsils, Peyer’s patches, lymphoid nodules in
GI tract, respiratory tract, urinary & reproductive
tracts
2 Types of Lymphoid Organs
• Central lymphoid organ: where lymphoid
precursor cells undergo antigen dependent
proliferation and differentiation
– T cells in thymus
– B cells in bone marrow
• Peripheral lymphoid organ: where
functional lymphocytes go including lymph
nodes, spleen, Peyer’s patches, lymphoid
nodules of GI and other tracts
Functional categories
• Primary lymphoid organs: antigen
independent; isolated from outside
“world”
– Bone marrow
– Thymus
– Bursa of Fabricius (birds)
• Secondary lymphoid organs: antigen
dependent; exposed to outside “world”
– MALT (BALT, GALT)
– Lymph nodes
– Spleen
Peripheral Lymphoid Tissues
• Lymphocytes contact antigens and divide
and differentiate into B cells and T cells
• Memory cells form that circulate for years
to provide extended immunity
Thymus 1
• Central lymphoid organ
• Thin capsule, lobular organization
• Each lobule has cortex (greater cell
density) with many T lymphocytes
surrounding lighter medulla
• Epithelial reticular cells
• Hassal’s corpuscles (flattened epithelial
reticular cells)
Thymus: cortex and medulla
Thymus cortex
Thymus medulla
Thymus 2
• Cortex: many lymphocytes,
macrophages, epithelial reticular cells
• Medulla: more epithelial reticular cells
and fewer lymphocytes
– mature T lymphocytes leave from here to
go to spleen and lymph nodes
– Hassal’s corpuscles: concentric layers of
epithelial reticular cells, core degenerated;
function/significance unknown
• After puberty thymus undergoes
involution and increases in connective
tissue and adipocytes
Lymphatic vessels
• Resemble veins (same 3 layers)
• Found throughout body except:
– Avascular tissues
– Central nervous system
– Splenic pulp
– Bone marrow
Lymph Nodes
• Number, location and size
– 100-200 clustered primarily in neck, thorax,
abdomen and pelvis; few in the extremities
– Absent from CNS
– Usually not located within other organs
– Size of watermelon seed to one-third that
size
• Difficult to palpate
Lymph Nodes
• Throughout body along lymph vessels
• Numerous in axilla, groin, cervical area
and thoracic/abdominal mesenteries
• Filter lymph before it returns to
vasculature
• Hilum, concave side, arteries, nerves
enter and veins leave
• Afferent lymph vessels enter convex
surface
• Efferent lymph vessels exit hilum
Lymph Nodes
• Capsule of dense irregular connective
tissue with incomplete septa
• Reticular fiber network
• Cortex: subcapsular sinus, peritrabecular
sinuses, several primary and secondary
(have germinal centers) lymphoid nodules,
venules may have thick endothelium
Lymph Nodes
• Lymphoid nodule germinal centers have
mitotic lymphocytes with surrounding B
cells
• Outside nodules is paracortical zone
where there are many T cells;
endothelium may be thickened
• Medulla has sinuses which join to form
efferent vessels
Lymph Node
Blood Flow
Legend:
a: arteriole
b: capillary
c: post - capillary venule d: muscular venule
Lymph node
Lymphatic vessel, lymph
node
Lymph node reticular stain
Cortex of lymph node with
lymphoid nodule
Lymph node medulla
Lymph node medulla with
sinusoid and medullary cords
Spleen 1
• Largest lymphatic organ
• Many macrophages; rbc phagocytosis
• Capsule of dense irregular connective
tissue w/ trabeculae dividing pulp
incompletely
• White pulp with lymphoid nodules
• Red pulp found between sinusoids has
reticular fibers, reticular epithelial cells
and macrophages
White Pulp
• Central arteries with encircling lymphoid
tissue
• T cells form periarterial lymphatic sheaths
(PALS) around small arteries
• Nodules are mostly B cells
• Reticular epithelial cells & macrophages
Red Pulp
• Reticular cells with cords of cells
between sinuses
• Cords have macrophages, monocytes,
lymphocytes, plasma cells, rbc,
granulocytes
• Sinuses have irregular lumen,
incomplete endothelium and basal
lamina
Spleen with red pulp and
white pulp
Spleen red pulp
Spleen white pulp with
surrounding red pulp
Functions of Spleen
• Lymphocyte production in white pulp
• RBC phagocytosis in red pulp
• T and B cells involved in immune
response
• Blood storage; small amount in humans
MALT - I
• Diffuse and solitary lymphoid
nodules: a portion of GALT and all of
BALT
• Unencapsulated lymphoid tissue
(multiple nodules)
– Peyer’s patches: (a portion of GALT)
• M (Microfold) cells: epithelial cells which
transport antigen
– Appendix (a portion of GALT)
MALT - II
• Partially encapsulated lymphoid tissue
(multiple nodules)
– Tonsils: palatine, lingual and pharyngeal
(tonsils are a portion of GALT).
– GALT is, therefore, any gut-associated
lymphoid tissue whether it takes the form of
diffuse LT, solitary lymphoid nodules, Peyer’s
patches, the appendix or the tonsils.
– GALT + BALT = MALT
Unencapsulated or Incompletely
Encapsulated Lymphoid Tissue
• Lymphoid nodules
• Tonsils: palatine, pharyngeal, lingual
• Peyer’s patches
Lymphoid Nodules
• Nodules of densely packed lymphocytes
located in digestive tract, respiratory tract,
urinary tract, and reproductive tract
• Most lymphocytes are B cells
Tonsils
• Incompletely encapsulated lymphoid nodules
• Palatine: covered by stratified squamous
nonkeratinized epithelium; crypts; underlying
connective tissue barrier
• Pharyngeal: covered by ciliated
pseudostratified epithelium, no crypts
• Lingual: smaller, at base of tongue; covered by
stratified squamous nonkeratinized epithelium;
one crypt in each nodule
Palatine tonsil
Pharyngeal tonsil
Peyer’s Patches
• Lymphoid nodules in the lamina propria of
the ileum (covered in detail in the digestive
tract section)