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.
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.
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
5- The dendritic cell :
– Birth: bone marrow.
– tissue distribution.
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 :
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.
Dr Benachour's course – Faculty of Constantine