Cells of the immune system

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Cells of the immune system

Dr Noura Daffa

Assistant Proffesor

Microbiology Immunology King abdulaziz University

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Contents

• Introduction

• Origin and development of immune cells

• Cells of the Innate immune system

• Cells of the Adaptive immune system

• Antigen-presenting cells (APCs)

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Introduction

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• The basic elements of the Immune system and responses are :

 variety of cells

 soluble molecules

• Cells of the immune system are mainly White blood cells (WBC), or Leukocytes which are found throughout the body i.e. in circulation and tissue.

• Although the leukocytes are central to all immune

responses, other cells in the tissues also participate in

the immune response.

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Introduction

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Introduction

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Introduction

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• Immune cells can be classified according

• Origin:

Myeloid

 Lymphoid

• Type of immune response:

Innate

Adaptive

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Neutrophils Eosinophils Basophils Mast cells

Monocytes/

Macrophages Dendritic cells

NK cells

CD8⁺ Tc lymphocytes CD4⁺ Th lymphocytes

B lymphocytes Myeloid

Lymphoid

PMN/

Granulocytes

Mononuclear cells

Cellular mediators

of immunity

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Origin and development of the immune cells

• All the great heterogeneity of the immune cells, mostly originate from Hematopoietic stem cells (HSCs)

 in the fetal liver, spleen and bone marrow during embryonic life

 and in bone marrow after birth and throughout life.

• HSC are undifferentiated “self-renewing cells”

• Development and differentiation of different cell lineages depend on:

 The microenvironment :

cell to cell interactions

cytokines.

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Innate immune system cells

• Includes

Monocytes/Macrophages

 Polymorphonuclear granulocytes (PMNs)

 Large Granular Lymphocytes (LGL) or Natural killer (NK) cells

• They recognize microbes through

 pathogen-associated molecular patterns (PAMP) receptors.

PAMP receptors have:

• broad specificity

• non-clonal distribution

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Monocytes / Macrophages

• Origenat from Myeloid precursor cell in the BM

• Long-life phagocytic cell

• Exist in the blood as Monocytes

& in tissues as Macrophages.

• Monocytes migrate from the

bloodstream to other tissues and differentiate into tissue resident macrophages, e.g. Kupffer cells in the liver.

• An important link between innate and the acquired immune

mechanisms

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Monocytes / Macrophages

Functions:

1. phagocytosis.

2. Are important (APCs) antigens are presented on its surfacein association with MHC II to T cells.

3. secrete IL-I , IL6 and tumor necrosis factor (TNF-  ),

prostaglandin and synthesize complement.

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Monocytes / Macrophages

4. kill antibody coated cells or tumor cells without

engulfing them ( ADCC)

5. Have Fc receptors & for C3b so enhancing the

uptake of organisms coated with antibodies

(opsonization)

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Monocytes / Macrophages

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Natural killer (NK) cells

• Also non as large granular Lymphocytes (LGL)

• Critical component of the innate immune system.

• lack most surface markers of B &

T cells.

• CD3 negative, CD56 positive

• Have receptors for the Fc portion of IgG )CD16) therefore kill

antibody coated cells (ADCC)

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Natural killer (NK) cells

Functions

 Rapid responses to

 virally infected cells

 tumor surveillance.

 Antibody-dependent cell-

mediated cytotoxicity (ADCC) (Cytotoxic without prior sensitization)

 Perforin and Granzymes

Target cell

Fc-R

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The adaptive immune system cells

• T cells and B cells

 Lymphocytes are responsible for the specific immune recognition of pathogens.

 They initiate adaptive immune responses.

 All lymphocytes are derived from bone marrow stem cells,

 but T lymphocytes (T cells) then develop in the thymus,

 while B lymphocytes (B cells) develop in the bone marrow (in adult mammals).

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T-lymphocytes

 constitute 65-80%

 Require antigens to be processed and presented to them to by specialized Antigen-presenting cells (APCs)

 Generate their effects generally either:

 by releasing soluble proteins, called cytokines, which signal to other cells.

by direct cell-cell interactions.

 T cells recognize antigens present on the surface of other cells using a specific receptor - the T cell antigen receptor (TCR) - which is quite distinct from, but related in structure to, the antigen receptor (antibody) on B cells.

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T-lymphocytes

• Types of T cell:

1. T helper 1 (Th1) cells

 interacts with mononuclear phagocytes and helps them destroy intracellular pathogens .

2. T helper 2 (Th2) cells

 interacts with B cells and helps them to divide, differentiate, and make antibody.

3. Cytotoxic T lymphocytes (CTLs or Tc cells).

 responsible for the destruction of host cells that have become infected by viruses or other intracellular pathogens

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T cell education within the Thymus

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T-lymphocytes

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Surface markers (receptors)

1. TCR

Consists of 2 polypeptide chains.

2.CD3 close to TCR 3.CD4

are called helper T (Th) cell their main function is to secrete

cytokines . OR 4.CD8

are called cytotoxic T (TC) cells,

kill virus infected & tumor cells. _CD3

TCR TCR

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T-lymphocytes

5. CD28

binds to B7 molecule on antigen presenting cell (APC)

6. CD40 ligand (CD40L)

binds to CD40on B cells

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The T cell antigen receptor (TCR)

V Vb

C Cb

Hinge

TCR is Monovalent Resembles an Ig Fab fragment

Fab

V_H V_L

Fc

C_L C_H

V_L V_H C_HC_L

C_HC_H C_H C_H

Transmembrane region

TCR is Never secreted

Domain structure: Ig gene superfamily

Cytoplasmic tail

Very short intracytoplasmic tail Antigen

combining site

Antigen combining site made of V and Vb regions

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T cell co-receptor molecules

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b  CD8

MHC Class I MHC Class II

3 b2

TcR TcR

CD4

T cell co-receptor molecules

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B-lymphocytes

• B cells

 30% of circulating lymphocytes

 They recognize antigens through surface antibodies

 The key cell of the Humoral immune response.

Surface receptors

Mature B cells bears

 IgM ,IgD. ( BCR )



Fc receptor for IgG

 CD40

 MHC II

(for antigen presentation to T cell ) ²⁸

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B-lymphocytes

• Functions

 Develop to Plasma B cells which produce and secrete Antibodies.

 Develop into memory B cells after activation.

 Perform the role of antigen-presenting cells (APCs) to T cell.

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Cluster of differentiation CD markers

• CD3 - a component of the T cell receptor complex.

• CD4 - a marker of helper T cells.

• CD8 - a marker of cytotoxic T lymphocytes (CTLs, Tc cells).

• CD28 - co-stimulatory molecules on T cells

• CD40L - co-stimulatory molecules on T cells

• CD5 - a marker of B-1 cells and marginal zone B cells.

• CD79 - a component of the B cell receptor complex.

• CD16 - a low affinity receptor for IgG, found on NK cells.

• CD56 - found on NK cells

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Antigen-presenting cells (APCs)

• Specialized group of cells, link the innate and adaptive immune.

• Includes:

1. Monocytes / Macrophages.

2. Follicular Dendritic cells (FDC) ： Germinal

centre of B cell area of lymph nodes & spleen.

3. Interdigitating (IDC) ： Paracortical area of lymph nodes (T cell area)

4. Langerhans cell: skin, draining lymph nodes .

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Summary

• Origin and development of immune cells

• Cells of the Innate immune system

• Cells of the Adaptive immune system

• Antigen-presenting cells (APCs)

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Thank you

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