Immunology 1 - Exam 1 Flashcards
Define:
Immunity
Antigens (immunogen)
Immunogenicity (antigenicity)
Immunity - host responses that prevent/combat infection and cancer.
Antigens (immunogens) - foreign substances, including pat of the infectious agent, that induce a specific immune response.
Immunogenicity (antigenicity) - ability to induce an immune response (all around us in nature).
Define:
Hapten
Epitope (antigenic determinant)
Antibody
Cytokines
Hapten - a molecule too small to elicit an immune response, unless attached to a larger molecule (protein).
> Note that haptens can be recognized by an existing immune response.
Epitope (antigenic determinant) - Part of the antigen that antibody or T cell receptor recognizes. A single antigen can have several of the same or different epitopes.
Antibody - protein that binds to a specific antigen which helps eliminate the antigen (produced by B cells).
Cytokines - Peptides produced by cells, often cells of immune system that help activate, suppress, or regulate other cells (like hormones of the immune system).
Describe different defenses and host responses that contribute to immunity.
- Physical barriers: skin, tears, mucus, etc.
- Commensal organisms: microbiota
- Innate immunity (nonspecific/natural immunity): resident. Induced (inflammation, activated macrophages).
- Adaptive immunity (specific and memory): humoral (antibody mediated). Cell mediated (effector T cells).
*Note: there is a lot of interactions and overlap between innate and adaptive immunity.
Describe innate (natural) immunity.
• Innate immune system responds without prior exposure.
• Immediate response against possible pathogen or irritant.
• Major components:
- Phagocytes (neutrophils, monocytes/macrophages)
- Natural-killer (NK) cells: kill virally infected and tumor cells. Produces cytokines.
- Complement: enhances phagocytosis, recruits cells, kills cells/bacteria.
• Inflammation - accumulation of fluids and WBCs t localize and remove irritant.
In adaptive immunity, describe B lymphocyte function.
- Recognizes native (whole) antigen.
- Produces antibody.
- One of the Ag presenting cells for T cells.
In adaptive (acquired) immunity, describe T lymphocyte function.
- Recognizes antigenic peptides presented by antigen presenting cells (dendritic cells, macrophages, and B cells).
- Regulates immunity, kills infected cells, activates macrophages, etc.
What are 2 major T cell populations?
• Cytotoxic T cells (CD8+ T cells) - kills virally infected and cancer cells. Kills cells with intracellular bacteria.
• Helper T cells (CD4+ T cells) -
- Th1 cells: cell mediated immunity (IL-2, INF-g, TNF-b, GM-CSF).
- Th2 cells: humoral immunity (IL-4, IL-5, IL-6, IL-13).
*Note: Different cytokines are characteristic of the 2 Th (T helper) cell subsets and determine function.
What are some examples of the multiple classes of antibody?
IgM - pentamer (first responder)
IgG - monomers (second responder, maternal antibody)
IgA - dimers (in secretions)
IgE - monomers (involved in allergic reactions, heparin/histamine)
IgD -
What are the 4 functions of Humoral (antibody-mediated) Immunity?
- Neutralization (binding inhibits activity)
- Opsonization (enhances phagocytosis)
- Complement activation (triggers complement activity)
- Antibody-dependent cell-mediated cytotoxicity (ADCC): cells (NK cells, macrophages, neutrophils) recognize antibody bound to target cell and release substances to destroy target cell.
Define Humoral (antibody-mediated) immunity?
When an antibody (immunoglobulin) specifically binds to an antigen and targets its destruction.
Th2 (T helper 2) cells typically play a role in humoral (antibody mediated) immunity.
What is cell-mediated immunity? What cells play a role?
Antigen-specific T cells play a major role.
- Cytotoxic T cells
- Activation of macrophages by Th1 (T helper 1) cells.
Th1 (T helper 1) cells typically play a role in cell-mediated immunity.
Describe the development of an immune response.
- Clonal selection
- Activation of lymphocytes requires more than antigen recognition.
> T cells recognize peptide bound to Major Histocompatibility Complex (MHC) molecules on antigen presenting cells (APCs).
- CD8+ T cells: MHC I - endogenous antigen
- CD4+ T cells: MHC II - exogenous antigen - Second co-stimulatory signal (i.e. interactions between other cell surface molecules on APC (antigen presenting cells) and T cells)
> Without the 2nd signal, anergy (unable to respond to antigen in future).
What are the 4 steps in clonal selection?
- A single progenitor cell gives rise to a large number of lymphocytes, each with a different specificity.
- Removal of potentially self-reactive immature lymphocytes by clonal deletion.
- Pool of mature naïve lymphocytes.
- Proliferation and differentiation of activated specific lymphocytes to form a clone of effector cells.
What are the benefits of clonal selection?
- Eliminate self-reactive cells
- Expand cells specific for antigen (more cells = quicker and greater responses).
Describe 4 forms of antigen qualities that impact immunity.
- Foreignness: the more similar to self, the less immunogenic due to tolerance against self.
> Hetero immunization - generation of immune response against antigens from an animal or another species. - The greater the size the more immunogenic. Small molecules will not generate immune response (i.e. drugs) unless they attach/modify self proteins (i.e. haptens).
> Physical form - particulate or aggregate antigens are more immunogenic.
> Denatured antigens are more immunogenic. - Composition: the more an antigfen, the greater immunogenicity. Protein > polysaccharides > DNA > lipid.
- Degradability: antigens (proteins) must be degraded to present to T cells.
