Cells and Tissues of the Cells and Tissues of the Immune SystemImmune System

AgendaAgenda

Cells of the Immune SystemCells of the Immune System Tissues/Organs of the Immune Tissues/Organs of the Immune

SystemSystem

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LymphocytesLymphocytes

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LymphocytesLymphocytes

B CellsB Cells T CellsT Cells NK CellsNK Cells

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B Cell T HelperCD4+

T CytotoxicCD8+

Lymphocyte Subsets

Naive Activated EffectorPhases of

LymphocyteActivation

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Accessory CellsAccessory Cells

Mononuclear PhagocytesMononuclear Phagocytes– Monocytes and MacrophagesMonocytes and Macrophages

Dendritic CellsDendritic Cells

Monocytes and Monocytes and MacrophagesMacrophages

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Dendritic CellsDendritic Cells Transport Antigens to L. nodesTransport Antigens to L. nodes InitiationInitiation of T Cell Responses of T Cell Responses

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Neutrophil

Eosinophil

Basophil

Thymus

Bone MarrowBursa

Peyer's Patches(Ruminants,Pigs)

Primary/Generative

Spleen

Lymph Nodes

Cutaneous

Mucosal

Secondary

Lymphoid Organs

Lymphoid OrgansLymphoid OrgansThe organs in which lymphocytes develop are called The organs in which lymphocytes develop are called

primary lymphoid organs (PLO)primary lymphoid organs (PLO)..

The organs in which mature lymphocytes reside and The organs in which mature lymphocytes reside and encounter Ag are calledencounter Ag are called secondary lymphoid organs secondary lymphoid organs

(SLO). (SLO).

D

Difference between PLO and SLO

CharactersCharacters PLOPLO SLOSLO

OriginOrigin Ectoendodermal Ectoendodermal junction or endodermjunction or endoderm MesodermMesoderm

Time of developmentTime of development Early in embryonic lifeEarly in embryonic life Late in fetal lifeLate in fetal life

PersistencePersistence Involute after pubertyInvolute after puberty Persists in adultPersists in adult

Effect of removalEffect of removalLoss of lymphocytesLoss of lymphocytesLoss of immune Loss of immune responseresponse

Nil or no effectNil or no effect

Response to antigenResponse to antigen UnresponsiveUnresponsive Fully reactiveFully reactive

ExamplesExamplesThymus, bursa of Thymus, bursa of Fabricius, Peyer’s Fabricius, Peyer’s patches etcpatches etc

Spleen, lymph nodes Spleen, lymph nodes etc.etc.

ThymusThymusEffect of removal/ Function•No. of circulating lymphocytes decreases•Presence of lymphocytes in T dependant area decreases•Failure in graft rejection

•Size is greatest in new born•Absolute size is greatest at puberty•Atrophies after puberty

Having two parts-1.Cortex- produce rapidly dividing thymocytes.

2.Medulla- within medulla, few round bodies are seen, called thymic / Hassall’s corpuscles.

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(T Cell Progenitors)

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Bone MarrowBone Marrow

Site of hematopoiesis.Site of hematopoiesis. Site of B cell maturation in mammals.Site of B cell maturation in mammals.

Bursa of FabriciusBursa of Fabricius• Site of B cell maturation in birds.• Found in birds but not in mammals.Having two parts-1. Cortex- contains lymphocytes, plasma cells and

macrophages2. Medulla- contains lymphocytes

Effect of removal/ Function•Presence of lymphocytes in T independent area decreases•Plasma cells in lymphoid tissues decreases•Serum immunoglobulins decreases •Antibody formation decreases

Peyer’s Peyer’s PatchesPatches

Site of B Cell Site of B Cell Maturation Maturation Found in Found in Pigs and Pigs and Ruminants Ruminants

Two types of PP-•Jejunal•Ileo-cecal

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Secondary Lymphoid OrgansSecondary Lymphoid Organs

Lymph NodesLymph Nodes Local sites of specific immune response.Local sites of specific immune response. Strategically placed on lymphatic channels.Strategically placed on lymphatic channels.

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SpleenSpleen Site of immunological responses against blood-Site of immunological responses against blood-

borne Ags.borne Ags. White pulpWhite pulp rich in lymphoid cells. rich in lymphoid cells. Red pulpRed pulp rich in myeloide cells. rich in myeloide cells.

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Evolutionary distribution of lymphoid tissues