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Professional antigen-presenting
cells (pAPCs)

Professional antigen-presenting cells are specialised cells in antigen presentation. They share the property of expressing, in the basal state, Class II HLA molecules – allowing the presentation of exogenous antigens – in addition to Class I HLA molecules expressed by all nucleated cells and platelets.

Dendritic cell

Dendritic cell

Dendritic cells are the pivot between innate immunity and adaptive immunity, the only cells capable of cross-presentation and capable of activating naive T cells.

Macrophage

Macrophage

Monocytes differentiate into macrophages, specialised in tissue phagocytosis allowing the ingestion and destruction of large particles (damaged or aged cells, foreign particles, bacteria, etc.).

B cell

B cell

B cells are the precursors of plasma cells, actors in humoral immunity, that is to say, mediated by antibodies. They are capable of recognising a native antigen.

See the characteristics of professional antigen-presenting cells (pAPCs)

Lymphocytes

Lymphocytes are the cells of adaptive immunity. We distinguish between T cells and B cells, which have many features in common, but also absolutely major differences.

See the general characteristics of lymphocytes and their main differences
T cells

T cells

T cells are actors in cellular immunity. They only recognise the antigen if it is presented by an HLA molecule.

B cell

B cell

B cells are the precursors of plasma cells, actors in humoral immunity, that is to say, mediated by antibodies. They are capable of recognising a native antigen.

Signalling of adaptive immunity

Adaptive immunity receptors (TCR and BCR)

Adaptive immunity receptors (TCR and BCR)

The term “adaptive immunity receptors” includes the TCR (T-Cell Receptor) and the BCR (B-Cell Receptor), respectively the antigen-specific receptors carried by T cells and B cells.

Antigen/antibody concept

Antigen/antibody concept

An antigen is a molecule specifically recognised by an adaptive immunity immunoreceptor (TCR and/or BCR). This recognition may lead to a specific immune response and therefore the generation of antibodies.

HLA molecules

HLA molecules

HLA molecules are key molecular actors, essential for the initiation of adaptive immunity, both cellular and humoral. They are an immunological obstacle to organ transplantation or haematopoietic stem cell transplantation.

Innate immunity signalling

Pattern Recognition Receptors (PRRs)

Pattern Recognition Receptors (PRRs)

Innate immunity receptors (Pattern Recognition Receptors) are intended to be “danger sensors” capable of inducing a specific inflammatory response conducive to the establishment of an adaptive immunological response if necessary.

Complement system

Complement system

The complement system describes an enzymatic cascade, the purpose of which is the production of the membrane attack complex, a powerful destructive agent for the membranes of pathogens (anti-pathogenic effect) and cellular membranes (cytotoxic effect).

DAMP

DAMP

DAMPs (Damage Associated Molecular Patterns) are molecular patterns originating from damaged cells or tissues, whatever the reason. These are nonspecific danger signals recognized by PRRs, which will then initiate the inflammatory response.

Cytokines

Cytokines

Cytokines are the messengers of the immune system. They allow the different actors to coordinate in time and space to put in place a proportional and adapted immune response.

KIR

KIR

KIRs (Killer Immunoglobulin-like Receptors) are receptors carried in particular by NK cells, whose main known ligands are Class I HLA class molecules (classical or non-classical).

Other cells and actors in immunity

Polymorphonuclear neutrophil

Polymorphonuclear neutrophil

Polymorphonuclear neutrophil are phagocytic cells of innate immunity.

NK Cell

NK Cell

NK cells are specific lymphocytes of innate immunity that possess certain characteristics of adaptive immunity.

Endothelial cell

Endothelial cell

Endothelial cells are the cells constituting the endothelia, that is to say the walls delimiting the blood vessels.

Bone marrow

Bone marrow

Bone marrow is the site of haematopoiesis and maturation of B cells.

Thymus

Thymus

Thymus is the site of T cell maturation.

Lymph node

Lymph node

Lymph nodes are the meeting place between lymphocytes and antigen. The encounter of a B cell with an antigen recognised by its BCR initiates the process leading to its activation; it is the same for the T cell via its TCR, with the difference that the antigen must be presented by a Class I or II HLA molecule.

Spleen

Spleen

The spleen is the meeting place between lymphocytes and antigen. The encounter of a B cell with an antigen recognised by its BCR initiates the process leading to its activation; it is the same for the T cell via its TCR, with the difference that the antigen must be presented by a Class I or II HLA molecule.