These lecture notes will provide an outline of information from the lectures. They are not complete. They should be used to help follow the lecture and as a guideline for information I think is important. You will need to fill in the gaps.


Chapter 19

These notes were updated March 18, 2001, and are ready for printing by Spring 2001 Med Micro. students.

I.    Immunity

A.    Innate 1.    Present from birth
2.    AKA nonspecific resistance
3.    Includes first and second lines of defense discussed previously (mechanical and chemical factors, phagocytosis, inflammation, fever, antimicrobial substances) B.    Acquired 1.    Begins after birth
2.    Includes humoral and cell-mediated immunity (third line of defense) II.    Acquired Immunity A.    Is either active or passive
B.    Is either naturally acquired or artificially acquired III.    Active acquired immunity A.    Long-lasting (usually life-long)
B.    Develops after exposure to the antigen has occurred in the host's body 1.    This exposure may occur "naturally" (NATURALLY ACQUIRED ACTIVE IMMUNITY) a)    It is accidental
b)    That is, the host unintentionally comes in contact with the antigen
c)    For example, a child plays with a child who has chickenpox (1)    One week later, that child develops chickenpox
(2)    He develops a primary antibody response (a)    Recall that this type of response results in IgM appear first in the circulation and followed much later by IgG (3)    After recovery, he will develop a secondary antibody response (a)    Recall that in a secondary antibody response, IgG is rapidly produced in extremely high concentrations as a result of memory cell formation 2.    This exposure may occur "artificially" (ARTIFICIALLY ACQUIRED ACTIVE IMMUNITY) a)    It is deliberate and planned
b)    That is, the host is intentionally exposed to the antigen
c)    For example, the infant (or adult) receives immunizations at the doctor's office (1)    The individual undergoes a primary and secondary antibody response IV.    Passive acquired immunity A.    Is short-lasting
B.    Is a "gift" of antibodies produced by a process occurring outside of the host's body [thus, the host never receives the needed information (the antigen) to generate his own antibodies] 1.    This acquisition of antibodies may occur "naturally" (NATURALLY ACQUIRED PASSIVE IMMUNITY) a)    This is also known as congenital immunity
b)    It occurs as a result of maternal antibodies transferring to the fetus through the placenta (1)    Recall that IgG is the only antibody capable of crossing the placenta c)    It occurs as a result of maternal antibodies transferring to the nursing baby through his mother's milk (1)    Colostrum (mothers' first milk) and breast milk contain IgA predominantly, with trace amounts of IgG and IgM 2.    This acquisition of antibodies may occur "artificially" (ARTIFICIALLY ACQUIRED PASSIVE IMMUNITY) a)    This occurs as a result of antibodies to a particular antigen being deliberately injected into the host
b)    These antibodies go by many names (1)    Antiserum is serum rich in one type of antibody
(2)    Hyperimmune serum has a higher than normal level of one antibody
(3)    Prophylactic serum is used to describe the antiserum that is injected to prevent a disease from occurring following a host's exposure to that disease
(4)    Therapeutic serum is used to describe the antiserum that is injected to assist a person's recovery from established disease
(5)    Convalescent serum is the blood sample removed from a patient recovering from an established disease (a)    It is often used to demonstrate the expected increase in the titer of circulating antibodies
(b)    This increase is the clinical proof or academic diagnosis of the disease (6)    Gamma globulin is another name for antiserum that is derived from the protein electrophoretic pattern that shows a distinct separation of antibodies from non-antibody proteins in a region called "gamma" (a)    Gamma globulin usually contains a mixture of antibodies, which will include the specific antibodies against the disease being prevented or treated C.    There is NO primary or secondary antibody response generated by the patient with passive acquired immunity V.    Vaccination A.    Preventative in scope
B.    Invokes ACTIVE ARTIFICIALLY ACQUIRED immunity 1.    Through an intentional exposure to antigen C.    Types of vaccines 1.    Inactivated virus or dead bacterial cells a)    Cannot multiply in human cells
b)    Viral xamples are the Salk polio virus vaccine and the vaccines against influenza and rabies
c)    A bacterial example is the old Diphtheria pertussis vaccine (1)    There are no modern-day examples of dead whole bacterial vaccines 2.    Attenuated virus or bacteria a)    Multiplies at low rates in the body and does not cause symptoms of disease (1)    This increases the dose of the antigen, resulting in a higher dose that causes a higher level of immune response b)    People receiving these are mildly contagious (1)    Antigens can spread to other people c)    Viral examples are the Sabin oral polio virus vaccine and the vaccines against measles, mumps, and rubella
d)    A bacterial example is the BCG vaccine against TB, which is not used in the US 3.    Whole agent a)    These are FIRST GENERATION VACCINES and are made up of the entire organism (viral or bacterial) or the entire bacterial toxin
b)    No whole bacterial organisms are used routinely for long-term protection against BACTERIAL disease
c)    There are a few used to provide temporary protection
d)    Examples are vaccines against bubonic plague and cholera (1)    Immunity does not last long because vaccine is weakly antigenic and does not cause memory cell production 4.    Toxoid a)    Is a whole agent vaccine and consists of chemically altered (formaldehyde) toxins, that provide protection against the toxin itself
b)    Examples include toxoids that protect against diphtheria and tetanus
c)    Patient forms antibodies against the toxin (IgG) 5.    Subunit a)    These are second generation vaccines (1)    These only contain parts of the whole agent (such as pili or capsule polysaccharides) b)    Examples include the vaccines for pneumococcal pneumonia and Haemophilus influenzae b 6.    Synthetic vaccine a)    This is a recombinant vaccine
b)    It is considered to be a third-generation vaccine (1)    These contain microbial fragments that are produced by genetic engineering
(2)    Once the antigen causing the immune response is identified, living cells are reengineered to produce the antigen
(3)    The size of the antigen mujst also be increased so that they are easily phagocytized (required for immune response to occur) c)    An example of this is the synthetic vaccine for hepatitis B, in which genes for a part of the viral protein coat of the hepatitis B virus are inserted into yeast cells, which then produce the proteins 7.    DNA vaccines a)    These are plasmids that have been engineered to contain a protein-encoding gene
b)    The plasmids are not able to replicate and are not infectious, and they only contain the code for the protein chosen
c)    These can be injected into the host to stimulate antibody production
d)    Presently, these are difficult to make as they require the inclusion of a promoter site and various other sequences of DNA in addition to the protein-encoding gene 8.    Adjuvants a)    Increase the efficiency of the vaccine or toxoid by making the antigen more "available" to the immune system
b)    Examples of adjuvants include aluminum sulfate and aluminum hydroxide, as well as mineral or peanut oil VI.    Serology A.    Serology is the use of laboratory tests to detect antigen and antibody reactions 1.    To diagnose infections
2.    To identify microorganisms
3.    To determine the immune status of an individual
4.    To type blood for blood banks and tissues for transplantation B.    There are two broad categories of serological tests 1.    Those that detect antibodies specific for a particular antigen (antigen is known; these are indirect tests)
2.    Those that use antibodies to detect an antigen (antibody is known; these are direct tests) VII.    Tests that detect antibodies specific for a particular, known antigen A.    These are used to determine whether a patient has mounted an immune response to a particular antigen
B.    This is the main method for diagnosis of viral infections
C.    Immune response is measured by titering the antibody
D.    Individuals exposed to infectious agents for the first time usually take 7-10 days to form DETECTABLE antibody
E.    The change from a negative serum (without the specific antibody) to a serum positive for the specific antibody is called SEROCONVERSION
F.    Serum is serially diluted (generally two-fold or ten-fold) and added to the same amount of antigen
G.    The inverse of the dilution that no longer contains detectable antibody is the "titer"
H.    The higher the titer, the higher the concentration of antibody
I.    The presence of IgM antibodies is a good indicator of active infection
J.    A four-fold (or 100-fold) increase in titer of IgG antibodies between two separate tests is also a sign of active infection
K.    Immunity (past infection) is proven by the presence of titers of IgG above a certain cut-off VIII.    Tests that use antibodies to detect an antigen A.    These are used to determine the presence or absence of a particular antigen in a patient test sample
B.    Known antibodies specific to the particular antigen are added to an unknown test specimen, and signs of a positive reaction are measured IX.    Neutralization Serologic Reactions A.    Reaction in which antigens and antibodies neutralize each other
B.    Used mainly to identify toxins/antitoxins and to diagnose viral diseases and determine the titer of host antibody to a virus
C.    Serum Ab + known virus = no reaction
D.    Can be performed in vitro or in vivo, in animals
E.    A NON-REACTION is a positive reaction in this case X.    Precipitation Serologic Reactions A.    Precipitin tests are based on the formation of antigen-antibody complexes in a lattice-work that precipitate from solution in a visible form
B.    The antigen is always soluble
C.    Can be performed in fluid or gel media
D.    Can be used to detect unknown antigens or antibodies
E.    Modifications include immunodiffusion, immunoelectrophoresis, and radial immunodiffusion techniques XI.    Agglutination Serologic Reactions A.    Based on interaction of a particulate (insoluble) antigen and a multivalent antibody such as IgG or IgM
B.    Cross-linking of the antibodies results in visible clumping of the particles
C.    Variations include hemagglutination (in this case, a NON-REACTION is a NEGATIVE reaction), complement fixation, and neutralization reactions (such as hemaglutionation inhibition described previously; in this case a NON-REACTION is a POSITIVE reaction)
D.    Direct tests generally look for unknown antigen; indirect tests for unknown antibody
E.    The Coombs Test is an example of a hemagglutination test 1.    Direct Coombs Test a)    Are there non-agglutinating antibodies attached to the RBC? 2.    Indirect Coombs Test a)    Are there non-agglutinating antibodies present in the serum? 3.    In both instances, a special antibody, called ANTI-HUMAN GLOBULIN (AHG) is used to detect the presence of a non-agglutinating antibody XII.    Flocculation Serologic Reactions A.    Combine the principles of precipitation and agglutination
B.    The antigen is a noncellular, PARTICULATE form
C.    It reacts with antibodies and forms large, visible aggregates
D.    One example is the VDRL test for syphilis 1.    This test uses a known antigen to find possible syphilis antibodies in the patient's serum XIII.    Complement Fixation Serologic Test A.    Used to detect antibodies that do not produce a visible reaction (precipitation/agglutination)
B.    Complement will bind to Ag-Ab complex ("fixed")
C.    An indicator (usually RBCs) demonstrates its fixation
D.    Lysis means complement is not fixed
E.    No lysis means complement was fixed
F.    An example of how this works: 1.    Patient's unknown serum is used to detect the presence of an antibody
2.    Treat the serum to destroy all of the patient's complement
3.    Now add the known antigen that is specific to the suspected antibody and complement a)    If the unknown serum contains the antibody, antigen-antibody complexes form
b)    If the unknown serum does not contain the antibody, there is only the antigen present 4.    The complement will bind to the antigen-antibody complexes and is unavailable for further reactions a)    If there are no antigen-antibody complexes, the complement is unbound and available for further reactions 5.    The last step is to add the indicator system a)    This system consists of red blood cells and a hemolysin
b)    In the presence of unbound complement, the hemolysin combines with the complement and causes the red blood cells to lyse
c)    If there is no unbound complement, the hemolysin is not activated to cause the red blood cells to lyse 6.    Lysis in this test means there were no antibodies present
7.    The absence of lysis is an indicator that antibodies were present XIV.    Fluorescent Antibody Serologic Tests A.    Used to identify microbes in clinical specimens (tissues)
B.    Also used to detect antibodies in serum
C.    Fluorescent dyes that fluoresce when exposed to ultraviolet light are used as the indicator
D.    Either the dye is attached to the known antigen or it is attached to the known antibody XV.    ELISA Serologic Tests A.    See pages 85-90 in lab notebook for full explanation
B.    Enzyme-linked immunosorbent assay
C.    Useful as a screen for HIV antibodies
D.    Positives always followed up with a confirmatory test XVI.    Gene Probes A.    This is a small DNA fragment having a single strand that searches for its complementary strand
B.    Once it finds its complement, it unites with it
C.    The DNA fragment is pre-treated with an indicator, usually a radioactive indicator
D.    If a union occurs, radioactive emissions are given off
E.    If no union occurs, there is no radioactive pulse
F.    An application of this technology is used in testing for M. tuberculosis






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