Introduction to Immunology
Immunity- “to protect”
- Purpose- to distinguish between self and non-self; destroy non-self
Acquired Immunity- response of lymphocytes to an antigen. The emphasis in medical school is on acquired immunity.
History
Cowpox- Jenner- 1798
Attenuated Vaccines- Pasteur- 1880
Blood Groups- Landsteiner- 1900
Innate Immunity
- all multicellular animals
- NON-SPECIFIC!!!!!
- Present at birth
- Initial Barrier
- Mediated by
- Physical barriers, Phagocytic cells (non-specific), Proteins, Secretions, and other chemical components, alternate pathway of complement system, fever, coughing, low pH of Vagina, commensal organisms of GI tract.
Acquired Immunity
- Extremely Specific, effective, and long-lasting
- inactive at birth
- response to an antigen
- occurs only after exposure to an immunogen
- Mediated by:
- Lymphocytes and their products, Accessory cells (i.e. macrophages), classical pathway of complement system.
Immunizations
- Active- immunization by exposure to antigen
- Passive- transfer of specific antibodies to a nonimmune person (gamma-globulin injection); is immediate
- Adoptive- form of Passive immunization resulting from transfer of CELLS
- Natural immunity- resulting from infection or environmental exposure to an antigen
- Artificial immunity- resulting from immunization
Characteristics of the Immune Response
A. Specificity
- determined by antigen-binding properties of the antibodies and T cell receptors
- Paratope- region of antibody and T-cell receptor molecules that bind to antigen
- Epitope- region of antigen that is recognized by antibodies or T cell receptors
- Can produce 10^7 to 10^8 different antibodies and T cell receptor molecules
B. Adaptiveness
- also called inducibility
- ability to respond to any molecule even if it is not natural
C. Discrimination between Self and Non-self
- Tolerance- antibodies or reactive T cells don’t attack self antigens
- Autoimmune diseases- breakdown in tolerance
D. Memory
- previous exposure to an antigen leads to faster, stronger, and morw specific responses
- In comparison with the antibody response following primary antigenic challenge, the antibody level following secondary antigenic challenge is typically:
1. quicker and persists for a longer period of time
2. attainable at a higher titre
3. IgG (in the primary response the appearance of IgG is preceded by IgM)
Cells involved in Acquired Immune responses
A. B-lymphocytes- precursors of Ab producing plasma cells
B. T-lymphocytes
- CD4+ T cells
a. helpers
b. Delayed-type hypersensitivity
- CD8+ T cells
a. suppressor activity
b. Cell-mediated cytotoxicity
C. Macrophages
- NOT antigen specific
- T cell activators
a. antigen processing and presentation
b. Production of the cytokine Interleukin 1 (IL-1)
- many other functions
CLONAL SELECTION THEORY
The most important concept in Immunology
1. Antigen Specificity is determined during B and T cell development before exposure to antigen.
- is the result of DNA rearrangement.
- Bunches of different DNA combinations are produced randomly, each given its own specificity
2. B and T cells express certain specific receptors on their surface that interact specifically with antigen during lymphocyte activation
- B cells- surface immunoglobulin
- T cells- T cell receptor
3. Each B and T cell expresses a unique Ag-specific receptor with a single-specificity. These lymphocytes can remain dormant until exposed to antigen that can bind with high affinity to the receptors of individual cells
4. Exposure to a given antigen results in activation, proliferation, and differentiation of only those lymphocytes that are specific for that antigen.
5. Lymphocytes reactive to the individual’s own proteins are ordinarily eliminated during their development, resulting in tolerance to self-antigens.
Humoral Immunity
- Antibody expression by plasma cells (B cell mediated)
1. each Ab molecule consists of 2 identical heavy and 2 identical light chains
2. Paratope (Ag-binding region) at the N-terminal of the H and L chains; called the variable or V region
3. Five different classes of antibodies: IgA, IgD, IgE, IgG, IgM
- respond to different HEAVY chain types (a,d,e,g,m)
Cell-Mediated Immunity
- T cell mediated
1. Cell-mediated cytotoxicity- direct killing of specific target cells by cel to cell contact with cytotoxic T cells
2. Delayed type hypersensitivity- recruitment and activation of macrophages by T cells. Important in protection against many infectious agents.
Regulation
1. Help- activities of helper T cells required for the responses of other lymphocytes to Ag because the helper T cells secrete cytokines which are regulatory proteins that act on other cells
2. Suppression- activities of suppressor T cells that inhibit immune responses
Manifestations of the Immune System
Positives- protection against infectious agents and tumors.
Negatives- Immunopathology, Allersies and Asthma, Autoimmune disease, Graft rejection.
Tags: Autoimmune diseases, B-lymphocytes, blood groups, cowpox, epitope, Immunology, Jenner, Landsteiner, Lymphocyte, Macrophages, paratope, Pasteur, Phagocytic cells, T-lymphocytes, vaccines
