Cells of & rsquo; immunity

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I- Introduction :

  • Most cells of the & rsquo; immunity originate in bone marrow.
  • 2 types of immune responses:

nonspecific and specific response Response :

  • cells: cell-mediated immune response.
  • Molecules in solution: humoral immune response.
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immunocompetent cells

II- nonspecific immunity :

1- polymorphonuclear :

  • Cells characterized by a multilobed nucleus.
  • Comprise in their cytoplasm granulations having different dye affinities when the smear is stained with MGG.

(MGG: May Grunwald Giemsa).

Thus the can into three categories:

  • neutrophil: fine granulations are neutral dyes.
  • eosinophils: large refractive granules orange.
  • Polynuclear basophils: grossesgranulatîons called red purple metachromatic.
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Granulocyte

A- Le polynucléaire neutrophile :

  • Plays a crucial role in & rsquo; innate immunity, because it is the lheck defense barrier against invasive pathogen.
  • It s & rsquo; based microbicide and cytotoxic effector contained in its granules.
  • Phagocytic cell short-lived.
  • 60 at 70% blood leukocytes.
  • core polylobé.
  • Grains intracytoplasmiques.
  • Differs from the myeloid stem cell in bone marrow.
  • Ability to migrate in response to a chemotactic signal.

  • Fixed and the phagocyte opsonized particles by complement and antibodies.
  • Destroyed very efficiently phagocytosed microorganisms.
  • Plays an essential role in the defense against extracellular multiplication in bacteria.
  • Involved in tissue damage immunopathological reactions involving complement and antibodies.

B- The polynuclear eosinophilic :

  • cytotoxic cell localized mainly in the tissues.
  • nucleus bilobed.
  • About 3% leukocytes.
  • Birth in bone marrow.
  • In short pass blood.
  • Skin and mucosal areas.
  • cytotoxic cell whose & rsquo; activity based on the content of granules.
  • Activation can be induced by antibodies capable of binding to the FcRs or some mediators.
  • Senior Officer of the fight against certain parasites.
  • Participates and anaphylactic reactions is increased in some vasculitis.

C- The basophil polynuclear :

  • Cell with nucleus polylobé often hidden by fifteen large granules.
  • spinal birth, distinct mast cell.
  • mature cell to its exit from the bone marrow.
  • Expresses receptors for IgE. (RFcεl).
  • dan s important defense mechanisms against certain parasites.
  • Reactions & rsquo; IgE anaphylaxis IgE dependent and independent.

2- the mast :

  • Birth in bone marrow.
  • Large cytoplasmic granules.
  • In short pass blood, tissue distribution.
  • functions: resulting in the release of the contents of their granules
  • high-affinity receptor for IgE.
  • Receivers for some additional degradation products.
  • Role in the fight against certain parasites.

3- Les monocytes/macrophages :

03 compartments :

  • medullary: seat precursors.
  • Sang : monocytes.
  • tissue: macrophages.

4- NK cells :

  • Natural killer cells.
  • 3th lymphocyte population.
  • Cell non T, no B.
  • No antigen-specific receptor.
  • Cell non-specific immunity: 1the body's defense barrier era.
  • Play an important role in:

– Infection Immunity.
– Anti-tumor immunity.

NK cells have morphological characteristics that distinguish :
– Big size.
– significant cytoplasmic volume.
– Granules intra cytoplasmiques.
– Two cytotoxic molecules: Perforine, granzymes.
– LGL : Large Granular Lymphocyte

Natural Killer (NK) cell

5- The dendritic cell :

– Birth: bone marrow.
– tissue distribution.

Division : at different parts of the & rsquo; body

III- specific immunity :

T cells and B have their surface antigen receptors (BCR, TCR) that allow them to make specific or adaptive immunity.

– TCR : T Cell Receptor
– BCR : B Cell Receptor

1- B lymphocytes :

– B cells provide humoral immunity due to the presence of specific antibodies.
– The precursors of B cells differentiate in the bone marrow in mammals.

A- Markers of B cells :

surface immunoglobulins :
– B cells make up about 5 at 15% blood circulating lymphocytes in humans.
– B cells are easily identifiable thanks to the presence on their surface immunoglobulin molecules.
– surface immunoglobulins are an excellent marker for B cells and represent the antigen receptor for the mature B lymphocyte.
– The majority of B cells in human blood express 2 immunoglobulin isotypes on their surface, IgM et IgD, holders of the same antigen specificity.

B- Ontogeny of B cells :

a- The stem cell immature B-cell :

Maturation and differentiation of B cells occurs at the level of the bone marrow in contact with non-lymphoid stromal cells.

It has four steps :
– pro early B cell
– Pro B cells late
– Pre B cell : synthèse et expression de la Chaine μ to the surface of the cells
– Cellule B immature : surface expression of lymphocyte of complete IgM.

b- Du lymphocyte B immature au lymphocyte B mature :

Within days the immature B cell will differentiate into mature B cells expressing IgM and the same antigen specificity surface IgD.

This stage of differentiation occurs in the peripheral lymphoid organs.

Within these organs the B cells will localize to the so-called T-independent areas.

After activation with a specific antigen mature B cells differentiate into plasma cells secreting antibodies.

2- T cells :

T cells: cell-mediated immunity comprising immunity vis-à-vis:
– bacterial or viral agents.
– Transplant rejection, tumor rejection.
– delayed hypersensitivity reactions.

The thymus plays an important role in the differentiation and maturation of T cells.

A- T cell marker :

The specific antigen receptor : TCR :

Figure 2. Key membrane markers of T cells.

B- Ontogeny of T cells :

– To differentiate adequately, thymocytes establish close contact with the cells of thymic stroma (epithelial cells, thymic macrophages and dendritic cells that strongly express MHC antigens including those of Class II).
– The subcapsular region is the first to be colonized by stem cells.
– There is a much more intense cell proliferation in the thymic cortex and found mainly immature cells that constitute 85-90% des thymocytes.
– Thymocyte maturation is accompanied by migration of the thymic cortex to the medulla.

On distingue 3 milestones :

– Stade In : Thymocytes triple-negative :
Derived stem cells from bone marrow, T cell precursors do not express membrane receptors CD3, CD4 and CD8, they are triple-negative thymocytes.

– Stade II : Thymocytes double positifs :
It concerns, at one point 85% thymus cells. It is characterized by the appearance of CD1 and coexpression of CD4 and CD8, thymocytes are double -positive.
It is at this stage that the rearrangement of genes coding for the TCR α chain takes place.
TCR low density will speak associated with the CD3 complex, on the surface of these thymocytes.

– Stade III : Thymocytes simple positifs :
Stage marked by increased expression of the receptor complex T / CD3, loss of CD4 or CD8, it is the single positive cells themselves.
At this stage thymocytes, are indistinguishable T cells from the periphery.

Negative selection occurs at the stage of single-positive thymocytes.

It is the elimination of thymocytes whose receptors recognize T with high affinity peptides self (self-reactive T cells).

At the end of maturing thymocytes from the thymus and peripheral lymphoid organs colonize.

Figure 1. Diagram of the intra-thymic maturation of T lymphocytes

Dr Benachour's course – Faculty of Constantine

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