STRUCTURE AND FUNCTIONS OF THE IMMUNE SYSTEM

MARYAM JAMILAH BINTI ABDUL HAMID082013100002IMS BANGALORE

LEARNING OUTCOME

Lymphoid organs

Central lymphoid organs

Peripheral lymphoid organs

INTRODUCTION

Lymphoid system:-

Lymphoid cells

Lymphocytes

Plasma cells

Lymphoid organs

Central (Primary)

Peripheral (Secondary)

Lymphoid Organs

Central Lymphoid OrgansPeripheral Lymphoid

Organs

Thymus Bursa of Fabricius SpleenLymph

nodes

Mucosa associated

lymphoid tissue (MALT)

CENTRAL LYMPHOID ORGANSTHYMUS

EMBRYOLOGY

3rd & 4th pharyngeal pouches

Mesenchymal stem cells (yolk sac, fetal liver and bone

marrow) reach thymus

Differentiate into thymic lymphoid cells (thymocytes)

Maximally relative size just before birth

Continues to grow about the twelve year

After puberty:

Spontaneous progressive involution

Functions best in early life

ANATOMY

Site: behind sternum

2 lobes surrounded by fibrous capsule

Outer cortex: actively proliferating small lymphocytes

Inner medulla: epithelial cells & mature lymphocytes (with

Hassall’s corpuscles)

MICROBIOLOGY PART

Production of thymic lymphocytes

Lymphocyte proliferation in the body

Acquire new surface antigens (‘Thy’ antigens)

Not dependent on antigenic stimulation

Prethymic lymphocytes are not

immunocompetent

‘Educated’ in thymus

Peripheral lymphatic tissue

BURSA OF FABRICIUS

BURSA OF FABRICIUSPouch from dorsal part of the cloaca

Day 15: becomes lymphoid organ

Near hatching: full functional ability

7-13 weeks age/puberty: involuting ( normally in

size and functional activity)

Immunocompetent 'bursal lymphocytes' or B cells

Migrate to SPLEEN (mantle, germinal follicles,

perifollicular regions) and LYMPH NODES (cortical

areas and medullary cords)

FUNCTION

Humoral immunity

Chicken BURSECTOMISED at hatching failed to form antibodies

when challenged with a bacterial antigen -Glick and Chang (1956)

Competence for Ig M production -early (Day 14 of embryonation)

Ig G late (about Day 21)

Birds bursectomised on Days 18 to 20 synthesize Ig M, but not Ig G

Peyer's patches; 20th week of gestation (spleen and lymph nodes)

Ig M > after birth

Ig G < 3rd month. Adequate by 2-3 years

PERIPHERAL LYMPHOID ORGANSLYMPH NODES

Cortex

Medulla

Cortical follicles and medullary cords

Intermediate zone

Filter for lymph

Proliferation of T cells and B cells

Local antigenic stimulation -ENLARGED 11

SPLEEN

Largest of the lymphoid organs

As a graveyard (effete blood cells)

White pulps and red pulps

Malphigian corpuscles

Germinal centre

'Mantle layer'

Marginal zone13

Thymus dependent area:

lymphatic sheath surrounds central arteriole

Bursa dependent (Thymus independent) area:

perifollicular region

germinal centre

mantle layer

A systemic filter trapping circulation bloodborne foreign

particles

MUCOSA ASSOCIATED LYMPHOID TISSUE (MALT)

Mucosa lining of alimentary, respiratory,

genitourinary and other lumina/surfaces that

constantly expose to numerous antigens

Rich lymphoid cells

Peyer's patches

Scattered isolated lymphoid follicles (MALT)

GALT (adenoids, tonsils to follicles of the colon)

BALT (respiratory tract)16

Cells: lymphoid cells, phagocytic cells, B cells and T

cells

Predominantly IgA -from mucosa

Free traffic of antigen-specific effector

lymphocytes between various mucosal and

secretory areas; 'common mucosal or secretory

immune system'

Lymphoid Organs

Central Lymphoid OrgansPeripheral Lymphoid

Organs

Thymus Bursa of Fabricius SpleenLymph

nodes

Mucosa associated

lymphoid tissue (MALT)

CONCLUSION

REFERENCES

Ananthanarayan and Paniker’s, Textbook

of Microbiology, 8th Edition

Dir. Prof. C P Baveja, Textbook of

Microbiology, 4th Edition