Probe Overview Ig DNA Unrearranged DNA shows as a single line. Rearranged DNA shows as a smear. I mRNA When T cell help ( CD40-CD40L) interaction occurs there is DNA rearrangement such that VH is joined to Cε; Iε is removed from the genome and the mRNA no longer contains it. If I mRNA is [...]

Topic Overview Adoptive Transfer Type of immunization involving the transfer of “sensitized” cells, serum or other components to a recipient. Hapten-Carrier Hapten-Carrier Hapten Carrier Protein ARS-OVA Azophenylarsonate Ovalbumin DNP-BGG Dinitrophenol Bovine gamma globulin LAC-HGG Phenyllactoside Human gamma globulin NIP-KLH S-nitrophenyl acetic acid Keyhole limpet hemocyanin TNP-BSA Trinitrophenyl Bovine serum albumin Haptens must be bound to [...]

Knockout Overview IL-6 You get normal development except there are no plasma cells. IL-6 is required for plasma cell development. AID AID is an enzyme needed for somatic hypermutation (affinity maturation, and more) and also isotype switching (cytokines are needed simultaneously for isotype switching). You get normal development of B and T cells. However all [...]

κλ Kappa (κ) and lambda (λ) are the two light chain isotypes. Antibody light chains have a constant region (IgCL) at one end and a variable region (IgVL) at the other end. Light chain variable regions are either kappa (κ) isotype or lambda (λ) isotype. The two light chain isotypes have no known functional differences. [...]

The mixed-lymphocyte reaction (aka the mixed-leukocyte reaction, or MLR) is an in vitro method for assaying TH cell proliferation and for generating a population of CTLs. When allogeneic (different MHC haplotype) lymphocytes are cultured together, TH cell populations expand. WIthin another 48 hours, an expanding CTL population is generated. The total proliferation of lymphocytes from [...]

The cell-mediated lympholysis assay (aka CML) assays CTL ability to lyse target cells. The target population (meant for lysis) is incubated in Na251CrO4, thus labeling the cells intracellularly with chromium-51 (aka 51Cr). The 51Cr cannot diffuse back out of the cells, so the only way 51Cr can be released back into the supernatent is if [...]

Intracellular Bacteria Mycobacterium species; Listeria monocytogenes. Intracellular Fungi Pneumocystis carinii; Candida albicans. Intracellular Parasites Leishmania spp.. Viruses All viruses are intracellular pathogens. For example, herpes.

Cross-linking of a membrane-bound immunoglobulin (mIg) with its complementary antigen initiates a signal transduction cascade that activates the attached B cell. Membrane-bound immunoglobulins have short cytoplasmic tails, rendering them unable to transduce activating signals on their own. However, each membrane-bound ligand-binding immunoglobulin associates with a single disulfide-linked signal-transducing heterodimer Ig-α/Ig-β to form the B cell [...]

When mature naïve B cell exit the bone marrow and begin recirculation, they are arrested in G0 and typically die within a few weeks unless they are activated by their complementary antigen. An activated B cells undergoes proliferation and differentiation into memory and plasma cells, going from G0 to G1, S phase and then mitosis [...]

The T cell receptor (TCR) is a T cell surface receptor that recognizes antigens presented by MHC molecules. It is a heterodimer composed of either α and β chains or γ and δ chains, and which interacts with another T cell surface component CD3. αβ T cells are usually highly specific (adaptive immunity), while γδ [...]

E2A E2A- mice do not express RAG-1, are unable to make DHJH rearrangements and fail to express λ5. EBF Early B-cell factor (EBF) is the same as E2A. BSAP Encoded by the Pax-5 gene, knockout B cells are arrested at an early developmental stage. Various B-cell-specific genes have promoters which bind BSAP, and absence of [...]

One of the central mechanisms of the immune system is thymocyte activation, clonal expansion and differentiation (into either effector or memory cells). T cells are activated by binding of the TCR-CD3 complex to a processed antigen peptide bound to a Class I (CD8 cells, aka cytotoxic T cells) or a Class II (CD4, aka helper [...]

The primary response is activation of naive thymocyte by a peptide-MHC complex. ∼48 hours after activation, the thymocyte enlarges into a blast cell and repeatedly divide to form a population of genetically identical cells (clonal expansion). Remember the G proteins described under transduction, and that G proteins help trigger the G1 phase of the cell [...]

Antibodies bind to antigens in a reversable non-covalent manner via hydrogen bonds, ionic bonds, hydrophobic interactions and van der Waal’s interactions. Antibodies only react with antigens in solution — as opposed to TCRs, which react with antigens bound to cell surfaces. These forces operate at short distances, so the antibody CDR (accounting for most of [...]

There are several different isotypes of heavy chain constant regions, broken into classes and subclasses. Classes are differentiated by large structural differences correlated to large functional differences. Subclasses have small but significant differences, also corresponding to separate functions. Most functions of antibodies are mediated (determined) by the heavy chain constant region. However, all antibody functions [...]

One problem with the study of antibodies was that they are heterogenous. For example, an electrophoresis pattern of an animal immunized against albumin (a homogenous protein) would show a spike of albumin and then several much smaller spikes of antibodies (meaning the albumin antibodies are polyclonal, or consisting of different subsets binding different sites on [...]

Type 1: Allergy Type I hypersensitivity (most commonly allergies) stem from overproduction of IgE. Thus, it requires an initial encounter so that isotype switching can occur — in secondary responses, the IgE crosslinks the antigen (and F(c)εRI and causes mast-cell and basophil degranulation. Atopic allergies and asthmatics are becoming more common in economically developed nations [...]

Traveling along chemical signals, thymocyte precursors migrate via blood from the bone marrow to the thymus. These cells have not yet rearranged their T cell receptor (TCR) genes and thus lack the T cell receptor (let alone CD3, CD4 or CD8); still lacking any characteristics of thymocytes, these immature T cells begin to divide furiously [...]

CD Overview CD1 Human CD1 is encoded by five non-polymorphic and closely linked (very near each other) genes on Chromosome 1. These genes — CdD1a,b,c,d,e — have an intron/exon structure similar to MHC Class I genes and encode proteins homologous (similar) to MHC Class I and MHC Class II proteins. However, CD1 proteins are able [...]

Mus musculus is the common house mouse. Its genome is the same size as that of human, with 20 chromosome pairs and 3×109 base pairs. Its life cycle takes two months, and gestation takes 21 days. The physical map of the genome is more complete than that of the human, making it relatively easy to [...]

Natural killer cells (NK cells) are part of the innate immune system. Instead of directly recognizing pathogens, natural killer cells monitor cell surface molecules indicative of pathogenesis. This sensitivity allows natural killer cells to vigorously initiate natural killer cytotoxicity (by emptying granules of porforin and granzyme) and inflammation as soon as pathogenesis is detected, and [...]

Macrophages (aka mononuclear phagocytes or mφs) have two main functions: phagocytosis and antigen presentation. In phagocytosis, the macrophage or monocyte cell-surface F(c) Receptor (FcR) binds to the antibody-antigen complex (an antibody bound to an antigen on the cell-surface of a pathogen). The pathogen, antigen and antibody are engulfed and degradative granules and enzymes break it [...]

There are five families of cytokine receptor, described below with their accompanying ligands. Immunoglobulin Superfamily Receptors IL-1, M-CSF, C-Kit Class I Cytokine Receptors IL-2,3,4,5,6,7,9,11,13,15, GM-CSF, G-CSF, OSM, LIF, CNTF, Growth Hormone, Prolactin Class II Cytokine Receptors IFNα, IFNβ, IFNγ, IL-10 Tumor Necrosis Factor (TNF) Receptors TNFα, TNFβ, CD40, Nerve Growth Factor (NGF), FAS Chemokine Receptors [...]

Lymph enters a lymph node via an afferent vessel, and leaves via efferent vessels. Inside the lymph node, lymph percolates through various layers of tissue. The lymph then continues on its path into the blood circulatory system. Reticular Cells Reticular cells are found throughout the node and help trap antigens passing through; also, reticular cells [...]

B cells (aka B lymphocytes) produce antibody when exposed to their complementary antigen. These antibodies can cause engulfment of infectious bacteria, neutralization of virions and induction of the complement cascade. In the bone marrow, B cells complete their hematopoietic differentiation from stem cells into IgM+,IgDweak immature virgin B cells. Next, in the medulla, B cells [...]

After understanding Clonal Expansion Theory, it is important to become familiar with the origin and nature of cells involved in the immune systems. Granulocytes and monocytes travel only in the blood. Lymphocytes circulate through both blood and lymph; lymphocytes can exit a lymph node via its efferent vessel, travel through the lymph and then enter [...]

Neutrophils are commonly referred to as polymorphonuclear neutrophilic leukocytes (PMNs/PMLs) or polys, even though technically any granulocyte is a PMN. Neutrophils are intensely phagocytic and arrive quickly at infection sites (unhealthy tissues) to phagocytize pathogens. Neutrophils have an F(c) receptor (FCR) which detects antibodies bound to antigens on the surface of pathogens. The process of [...]

The discovery of B cells led to a modern theory of antibody production called Clonal Expansion Theory (sometimes still referred to as Clonal Selection Theory). In Clonal Expansion Theory, B and T cells are created with random antibodies, then screened for self-reactivity. When antigen enters the system, it eventually binds to any B cell displaying [...]

Instructional theories postulate that antigens play a central role in determining antibody specificity. Conversely, selective theories state that an antigen reacts with an already-existing antibody. Selective theories better explains acquired immune responses. Below is a history of antigen-antibody theories. Researcher Experiment/Theory Paul Ehrlich ∼1900 According to Ehrlich’s Side Chain Theory, an antigen binds to a [...]

Note: This author uses the phrases ‘acquired immunity’ and ‘adaptive immunity’ interchangeably. ‘Immune response’ refers to aspects of the immune system which are antigen-specific. Adaptive immunity is triggered when an infection eludes innate defenses and generates a threshold of antigen. Acquired immunity is effective only after several days, the time required for antigen-specific T and [...]

Innate immunity is a non-specific inherited defense system that provides a general response against all pathogens. Innate immunity provides the body’s first protection against invaders (on the other hand, acquired immunity — aka adaptive immunity — responds to a persisting infection). Innate immunity stimulates adaptive immunity, influencing its expression to optimize its response against the [...]

The inflammatory response is characterized by the following three events: Vasodilation. Vasodilation is an increase in blood vessel diameter. Permeability. Capillaries increase in permeability, allowing exudate to flow to and swell the site of inflammation. Phagocyte influx. An influx of phagocytes consists of three steps: margination, where phagocytes adhere to the capillary endothelium; extravasation, where [...]

The cells of the immune system function to combat viruses in two ways: B cells secrete antibodies which neutralize the virus (humoral immunity) and T cells recognize and kill infected cells (cell-mediated immunity) In addition, interferon activity is very effective. Just a few molecules of interferon bound to the surface of a cell can protect [...]

Interferon (IFN) is secreted by avirally infected cell, and induces an anti-viral state in surrounded cells. It is too late for the infected cell, which dies, but the surrounding cells might be saved. It is not a single protein, but rather a group of stable (acid pH) proteins of 17,000 d secreted by different cells [...]

The major histocompatibility complex (MHC) is present in all vertebrates, and is encoded by a group of genes called HLA in humans and H-2 in mice. Products of these genes are mostly cell surface glycoproteins involved in antigen presentation. MHC molecules must be bound to a peptide (it does not even have to be pathogenic) [...]

After hematopoiesis in the bone marrow, granulocyte-monocyte progenitor cells differentiate into promonocytes. These promonocytes enter the bloodstream, where they mature further into monocytes; monocytes enlarge five- to ten-fold and become phagocytic while circulating for about up to three days in the blood. Next, these monocytes extravasate into tissues, where they become either fixed (tissue-specific) or [...]

Antigens are foreign bio-organic molecules that interact with B cells (via antibodies) and T cells (via T cell receptors). Blood-borne antigens are concentrated in the spleen; lymph-borne antigens are concentrated in nearby lymph nodes and nodules. Upon detection by the acquired immune response, antigens stimulate production of antigen-specific antibodies. Toxins, invading bacteria and viruses, and [...]

So Many Names For T Cells! T cells — also known as T lymphocytes or thymocytes — are broken into two classes: CD8+ T cells, which are T cells which express CD8 cell surface proteins; and CD4+ T cells, which express CD4 cell surface proteins and are called TH cells. All T cells contain a [...]

The most important function of the human immune system occurs at the cellular level of the blood and tissues. The lymphatic and blood circulation systems are highways for specialized white blood cells to travel around the body. White blood cells include B cells, T cells, natural killer cells, and macrophages. Each has a different responsibility, [...]

What Is the Lymphatic System? Blood in the heart is highly pressurized, but most of that pressure is lost as blood flows through arteries and then arterioles. At the capillary level, most remaining pressure is lost as blood leaks out into tissues. This leaked fluid is unable to go against the pressure gradient back into [...]

Cell-mediated immunity is an immune response that does not involve antibodies but rather involves the activation of macrophages and natural killer cells, the production of antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen. These mechanisms are described below. Cell-mediated immunity is directed primarily at microbes that survive in phagocytes [...]

Antibody production by activated B cells is the core the humoral response: antibody effects, such as complement activation by IgM and certain IgGs, opsonization via F(c)Rs and pathogen/toxin neutralization by high-affinity IgG and IgA; and processes related to B cell activation, such as TH2 activation and cytokine production, germinal center formation, isotype switching, affinity maturation [...]

The immune system has evolved to deal with invasion by microbial pathogens. The main task of the immune system is to distinguish self from non-self. The immune system must not attack and destroy self, but it must eliminate whole organisms (such as bacteria and fungi) as well as intracellular pathogens (such as viruses). Connected by [...]

Antibodies (aka immunoglobulin or Ab) are produced by B cells and specifically bind to antigens (aka Ag) in solution (as opposed to TCRs, which bind antigens on cell surfaces). An antigen is any substance that binds specifically to a T cell receptor or B cell receptor. This antibody-antigen binding can: cause the antigen to be [...]