Author(s): David Dorward, Hannah McManus and Genevieve McMahon
Adaptive immune response – the response consisting of antigen-specific lymphocytes following the clonal expansion of these in response to the antigenic stimuli.
ADCC – Antibody-dependent cell-mediated toxicity (when cells need antibody recognition in order to kill a cell)
Afferent – carrying lymph towards the lymph node.
Affinity – the strength of binding of one molecule with another e.g. an antigen with the Fab fragment of an antibody
Affinity maturation – the increase in affinity for a particular antigen which occurs as an adaptive immune response progresses, as well as in subsequent encounters with the same antigen.
Apoptosis – programmed cell death.
Base excision repair – a cellular mechanism that repairs damaged DNA throughout the cell cycle. It does this by removing small, single base lesions from the genome.
Chemokines – small proteins which act as chemoattractants, encouraging the migration and activation of various cells such as lymphocytes via their chemokine receptors.
Class switching – a process whereby activated B cells undergo a somatic recombination process to change the heavy chain constant region gene with another coding for a different isotype; this results in a change in the production of antibodies from IgM to either IgG, IgE or IgA isotypes and hence an alteration in effector function.
Cognate antigen – the antigen which is of the correct shape to interact with a BCR or TCR.
Dark zone – Where centroblasts go through proliferation and mutation in the germinal centre
Degranulation – where cells release cytotoxic or other molecules from secretory vesicles (granules) found inside the cell out into the extracellular environment.
Differentiate – the process whereby cells become more specialised through alteration of their gene expression.
Efferent – carrying lymph away from the lymph node.
Extravasation – the migration of a cell out of the vasculature and into the surrounding tissue, usually via HEVs.
Follicle – an area within a peripheral lymphoid organ made up primarily of B cells with some follicular dendritic cells.
Germinal centre – areas within lymphoid follicles where B cells undergo intense proliferation and differentiation during an adaptive immune response; in particular, these are the site of somatic hypermutation and class switching.
HEV – high endothelial venules; specialised small blood vessels in lymphoid tissues allowing lymphocytes to extravasate into the lymphoid organs.
Introns – noncoding sections of an RNA transcript that are removed before the RNA is translated into a protein
Light zone – where the selection of the centrocyte occurs in the germinal centre.
Lymphatics – the system of vessels similar to veins which carry lymph throughout the body.
Mismatch repair – a system which recognises and repairs erroneous insertion or deletion of bases that can occur during DNA replication, while also being responsible for repairing DNA damage.
Naïve – lymphocytes which have not yet encountered their cognate antigen following maturation.
Neutralisation – the binding of antibody to an antigen to prevent it from causing harm
Opsonisation – the binding of antibody to cells or molecules to allow them to be recognised by immune cells to speed up the detection process.
Paratope – the part of the antibody that binds antigen
Primary lymphoid organ – The thymus and bone marrow, where immature T and B cells respectively mature.
Secondary lymphoid organ – also known as peripheral lymphoid organs, specially designed to facilitate the interaction between APCs and the mature naive lymphocytes as they circulate.
Sinusoids – small blood vessels.
Somatic hypermutation – a programmed process of mutation to change the affinity of the variable regions of immunoglobulin genes
V region – variable region of the gene
APC – Antigen Presenting Cell; cells which can process antigens to display as peptides on MHC Class II alongside the necessary co-stimulatory molecules required for T cell activation. Dendritic cells are the ‘professional APCs’, but macrophages and B cells also have the ability to act as APCs.
Centroblasts – rapidly dividing B cells found in the dark zone of the germinal centres, within follicles in the secondary lymphoid organs.
Centrocytes – mature centroblasts found in the light zone of the germinal centres, within follicles in the secondary lymphoid organs.
Follicular Dendritic Cells – cells which are similar in appearance to dendritic cells, with long processes that interact with B cells in the follicles of peripheral lymphoid organs, assisting in the selection of high-affinity B cells.
Lymphocytes – a class of white blood cell which possess an antigen-specific receptor and clonally expand upon interaction with their cognate antigen. The two main classes are B and T lymphocytes, which mediate humoral and cell-mediated immunity respectively.
Memory B cell – Lymphocytes which remain following an initial exposure to an antigen, and which can provide rapid, sensitive responses upon re-exposure to the same antigen.
Plasma cell – a terminally differentiated B lymphocyte which produces large quantities of antibody.
Stromal cells – connective tissue cells which support the parenchymal cells of an organ.
T follicular helper cells – CD4+ T cells involved in assisting B cell formation in the germinal centre.
Tingible body macrophages – a specialised macrophage found predominantly in germinal centres, containing the apoptotic B cells.