B cell Plasma cell
B cells are responsible for humoral immunity, and as such are one of the effector pillars of adaptive immunity in the same way as T cells. They are also professional antigen-presenting cells.
Haematopoiesis / cytology
B cells
Cytological characteristics and the main principles of B cell ontogeny are described here
Plasma cells
Some B cells become plasma cells. In the physiological state, they are found in the secondary lymphoid organs where they are generated (more specifically within secondary follicles) or in the bone marrow where they return to nest (see B cell activation). They are theoretically not circulating cells.
It is a large oval cell whose nucleus is eccentric within a large basophilic cytoplasm, testifying to the intense activity of protein synthesis since the plasma cell is specialised in the synthesis of immunoglobulins (= antibodies) that will be secreted.
Functions
Antigen presentation
B cells have the mechanisms necessary for the presentation of endogenous antigens in the same way as all nucleated cells and platelets. They have the particularity – shared with all so-called professional antigen-presenting cells – of expressing in addition Class II HLA molecules allowing the presentation of exogenous antigens. These antigens are internalised after binding to the BCR, which recognises native antigens. Unlike dendritic cells, they are not capable of cross-presentation (no cross-presentation).
Cytokine synthesis
These cytokines are of crucial importance for T/B cell cooperation, which allows total and complete activation of these two cell types (see T cell activation / B cell activation).
Plasma cells: synthesis of antibodies (or immunoglobulins)
At the end of its activation, B cell becomes a plasma cell specialised in the synthesis of antibodies (immunoglobulins). These antibodies are of major importance for:
- Complement activation
- ADCC (Antibody Depedant Cell Cytotoxicity)
- Opsonization
What needs to be remembered
B cells are effector cells of adaptive immunity, particularly humoral, because plasma cells are the only cells capable of producing antibodies. These antibodies are of major importance in the context of transplantation, which is why B cells are the target of immunosuppressants. There are also techniques to eliminate or render non-functional antibodies.
