Defining The Players
What are immunogens?
These molecules are defined by their ability to induce a specific immune response, such as the production of antibodies or the activation of T cells
In humans, the Major Histocompatibility Complex (MHC) locus is designated by this three-letter acronym.
What are dendritic cells, macrophages, and B cells?
These are the three "professional" APCs that primarily express Class II MHC molecules.
What is the Endoplasmic Reticulum?
This cellular organelle is the site where newly synthesized Class I and Class II MHC molecules are assembled.
What is the antigen?
In the "Two-Signal" hypothesis for T cell activation, Signal 1 is always provided by this.
What are haptens?
This term refers to small molecules that are not immunogenic on their own but can react with specific antibodies once an immune response has been initiated.
What is co-dominant expression?
This feature of MHC expression ensures that both parental alleles of each MHC gene are expressed, increasing the variety of peptides that can be presented.
What are Langerhans cells?
These specific dendritic cells reside in the epidermis and are phenotypically immature until they capture a microbial antigen.
What is the proteasome?
In the Class I pathway, cytosolic proteins are degraded into peptides by this large enzymatic complex.
What is MHC restriction?
CD4+ T cells only recognize peptides bound to Class II MHC, while CD8+ T cells are restricted to Class I; this phenomenon is known as this.
What is a paratope?
This is the specific area on an antibody molecule that interacts with and is totally complementary to an antigen's epitope.
What is B2-microglobulin?
This non-polymorphic, invariant polypeptide chain is noncovalently associated with the Class I MHC alpha chain at the cell surface.
What are plasmacytoid dendritic cells?
This subset of dendritic cells is the major producer of Type I Interferons during innate immune responses to viral infections.
What is TAP (Transporter associated with Antigen Processing)?
This protein complex is responsible for transporting peptides from the cytosol across the ER membrane to meet Class I MHC molecules.
What is cross-presentation?
This term describes the process where a dendritic cell ingests a virally infected cell and presents those viral antigens on Class I MHC to activate naive CD8+ T cells.
What are proteins, polysaccharides, lipids, and nucleic acids?
While T cells only recognize peptides, B cell receptors can recognize these four major types of macromolecules in their native conformation
What is Interferon-gamma?
This cytokine is the primary signal responsible for increasing the level of MHC molecule expression on cell surfaces.
What are follicular dendritic cells?
These specialized cells in the lymphoid follicles display antigens coated with antibodies or complement to B cells to help select high-affinity B lymphocytes.
What is the Invariant chain?
This molecule occupies the peptide-binding cleft of Class II MHC molecules in the ER to prevent them from binding to endogenous peptides.
What are costimulators?
These membrane proteins, expressed by APCs only in the presence of microbes, serve as Signal 2 for T cell activation.
What are TNF and IL-1?
These two primary inflammatory cytokines are produced by APCs following TLR signaling to activate and mature dendritic cells.
What is graft/organ rejection?
MHC molecules were originally named for their role as the primary targets in this clinical/experimental phenomenon between genetically different individuals.
What are chemokines?
Mature dendritic cells utilize these proteins, produced in lymphatic vessels, to navigate from the site of infection to the draining lymph nodes.
What is HLA-DM
This HLA molecule, found in endosomes, is responsible for the removal of CLIP and the subsequent loading of antigenic peptides onto Class II MHC.
What is degenerate (or broad specificity)?
Because MHC molecules can bind many different peptides with similar anchor residues, their binding specificity is described by this term.