Dictionary#2: Hapten & Epitope

Hapten – A low-molecular-weight molecule that can be made immunogenic by conjugation to a suitable carrier.

How Haptens Work (Flash Animation)

Haptens are antigenic but incapable by themselves of inducing a specific immune response. In other words, they lack immunogenicity. A hapten is a small molecule that can elicit an immune response only when attached to a large carrier such as a protein; the carrier may be one that also does not elicit an immune response by itself. (In general, only large molecules, infectious agents, or insoluble foreign matter can elicit an immune response in the body.) Once the body has generated antibodies to a hapten-carrier adduct, the small-molecule hapten may also be able to bind to the antibody, but it will usually not initiate an immune response; usually only the hapten-carrier adduct can do this. Sometimes the small-molecule hapten can even block immune response to the hapten-carrier adduct by preventing the adduct from binding to the antibody.

Epitope – The portion of an antigen that is recognized and bound by an antibody or TCR-MHC combination; also called antigenic determinant.

An epitope, also known as antigenic determinant, is the part of a macromolecule that is recognized by the immune system, specifically by antibodies, B cells, or T cells. The part of an antibody that recognizes the epitope is called a paratope. Although epitopes are usually thought to be derived from nonself proteins, sequences derived from the host that can be recognized are also classified as epitopes. Most epitopes recognized by antibodies or B cells can be thought of as three-dimensional surface features of an antigen molecule; these features fit precisely and thus bind to antibodies. Exceptions are linear epitopes, which are determined by the amino acid sequence (the primary structure) rather than by the 3D shape (tertiary structure) of a protein. T cell epitopes are presented on the surface of an antigen-presenting cell, where they are bound to MHC molecules. T cell epitopes presented by MHC class I molecules are typically peptides between 8 and 11 amino acids in length, whereas MHC class II molecules present longer peptides, and non-classical MHC molecules also present non-peptidic epitopes such as glycolipids.

Reflections#1: Study of Immunology Class

It is already been almost 3 weeks from the beginning of the spring 2010 semester. Immunology class is the most fun class so far. It is very small class but I am having fun and want to learn more and more about the Immunology. Of course that it is Dr. V's class and there are a lot of assignments to work on; however all assignments are valuable whether it is short or long and it makes me understand better. I am a visual learner and I make copies of image I saw and learned to save to the brain. There are tons of images in this class and it is little difficult to keep up with; however I am trying not to miss anything. Subjects of Immunology give me to think about my childhood. I was kind of clumsy boy and I fell down to the ground surface a lot when I was walking and running. Of course I had a lot of small wounds and scars all over the legs. I was always curious about the healing process of my wounds. How my body clogs the blood in the wounded area so quickly? How my body components fight with infections? How my body regenerate the skin? Etc... I am learning about these kind of questions and already solved from the Immunology class but I want to learn more deeply about our immune system for this semester.

Dictionary#1: Opsonin & Mast Cell

Opsonin - A substance (e.g., immunoglobulins, complement) that promotes the phagocytosis of antigens by binding to them.
The macrophage membrane has receptors for certain classes of antibody. If an antigen is coated with the appropriate antibody, the complex of antigen and antibody binds to antibody receptors on the macrophage membrane more readily than antigen alone and phagocytosis is enhanced. Thus antibody functions as an opsonin, a molecule that binds to both antigen and phagocyte, thereby enhancing phagocytosis. The process by which opsonins render particulate antigens more susceptible to phagocytosis is called opsonization.

Mast Cell - A bone-marrow-derived cell present in a variety of tissues that resembles peripheral blood basophils, bears Fc receptors for IgE, and undergoes IgE-mediated degranulation.Mast cell precursors, which are formed in the bone marrow by hematopoiesis, are released into the blood as undifferentiated cells; they do not differentiate until they leave the blood and enter the tissues. Mast cells can be found in a wide variety of tissues, including the skin, connective tissues of various organs, and mucosal epithelial tissue of the respiratory, genitourinary, and digestive tracts. Like circulating basophils, these cells have large numbers of cytoplasmic granules that contain histamine and other pharmacologically active substances. Tissue mast cells are related to but distinct from, basophils. Mast cells play an important role in the development of allergies. Mast cells increased numbers during allergies.

References: Kuby Immunology 6th Edition. Pictures are directly linked to websites.

Personal Feedback: I confused these two words, opsonin and mast cell; therefore I wanted to study little more and make sure I really know about these words of Immunology.

Written by D.J. Kim