1
Q
Hypersensitivity Reactions can be divided into four classes: type I, II, and III are immediate reactions based on humoral immunity
A
Type IV is a delayed reaction based on cell-mediated immunity
2
Q
Allergies and the Microbiome:
A
-childhood exposure to microbes may decrease development of allergies
3
Q
Type I (Anaphylactic) Reactions
A
- anaphylactic reactions involve the production of IgE antibodies that bind to mast cells and basophils to sensitize the host
- the binding of two adjacent IgE antibodies to an antigen causes the target cell to release chemical mediators, such as histamine, leukotrienes, and prostaglandins, which cause the observed allergic reactions
- systemic anaphylaxis may develop in minutes after injections or ingestion of the antigen; this may result in circulatory collapse and death
- localized anaphylaxis is exemplified by hives, hay fever, and asthma
- skin testing is useful in determining sensitivity to an antigen
- desensitization to an antigen can be achieved by repeated injections of the antigen, which leads to the formation of blocking (IgG) antibodies
4
Q
Type II (Cytotoxic) Reactions
A
- Type II reactions are mediated by IgG or IgM antibodies and complement
- the antibodies are direct toward foreign cells or host cells. complement fixation may result in cell lysis. Macrophages and other cells may also damage the antibody-coated cells
- human blood may be grouped into four principle types, designated A, B, AB, O
- the presence or absence of two carbohydrate antigens designated A and B on the surface of the RBC determines a person’s blood type
- naturally occuring antibodies against the opposite AB antigen are present in serum
- incompatible blood transsusions lead to complement-mediated lysis of the donor RBCs
- the absence of the Rh antigen in certain individuals (Rh-) can lead to sensitization upon exposure to it
- When an Rh- person receives Rh+ blood, that person will produce anti-Rh antibodies. Subsequent exposure to Rh+ cells will result in a rapid, serious hemolytic reaction
- An Rh- mother carrying an Rh+ fetus will produce anti-Rh antibodies. Subsequent pregnancies involving Rg incompatibility may result in hemolytic disease of the newborn (HDNB)
- HDNB can be prevented by passive immunization of the mother with anti-Rh antibodies
- in the disease thrombocytopenic purpura, platelets are destroyed by antibodies and complement
- agranulocytosis and hemolytic anemia result from antibodies against one’s own blood cells coated with drug molecules
5
Q
Type III (Immune Complex) Reactions
A
- immune complex diseases occur when IgG antibodies and soluble antigen form small complexes that lodge in the basement membranes of cells
- subsequent complement fixation results in inflammation
- glomerulonephritis is an immune complex disease
6
Q
Type IV (Delayed Cell-Mediated) Reactions
A
- delayed cell-mediated hypersensitivity reactions are primarily due to T cell proliferation
- sensitzed T cells secrete cytokines in response to the appropriate antigen
- cytokines attract and activate macrophages and initiate tissue damage
- the tuberculin skin test and allergic contact dermatitis are examples of delayed hypersensitivities
7
Q
Autoimmune Diseases:
A
- autoimmunity results from loss of self-tolerance
- self-tolerance occurs during fetal development; T cells that will target host cells are eliminated through thymic selection (clonal deletion)
- The immune system attacks the myelin sheath of nerves in MS
- Graves’ disease, myasthenia gravis, and rheumatoid arthritis are immune complex automimmune diseases
- insulin-dependent diabetes mellitus and psoriasis are cell-mediated autoimmune reactions
8
Q
Reactions to Transplanation:
A
- MHC self molecules located on cell surfaces express genetic differences among the individuals, these antigens are called HLAs in humans
- To prevent the rejection of transplants, HLA and ABO blood group antigens of the donor and recipient are matched as closely as possible
- transplants recognized as foreign antigens may be lysed by T cells and attacked by macrophages and complement-fixing antibodies
- transplanation is a privileged site (such as the cornea) or of a priviledged tissue (such as a pig heart valve) that does not cause an immune response
- pluripotent stem cells differentiate into a variety of tissues that may provide tissues for transplants
- four types of transplants have been defined on the basis of genetic relationships between the donor and the recipient: autografts, isografts, allografts, and exenotransplantation products
- bone marrow transplants (with immunocompetent cells) can cause graft-versus-host disease
- successful transplant surgery often requires immunosuppression drugs to prevent an immune response to the transplanted tissue
9
Q
The Immune System and Cancer:
A
- cancer cells are normal cells that have undergone transformation, divide uncontrollably, and possess tumor-associated antigens
- the response of the immune system to cancer is called immunological surveillance
- cytotoxic T lymphocytes recognize and lyse cancerous cells
10
Q
The Immune System and Cancer:
A
- cancer cells are normal cells that have undergone transformation, divide uncontrollably, and possess tumor-associated antigens
- the response of the immune system to cancer is called immunological surveillance
- cytotoxic T lymphocytes recognize and lyse cancerous cells
11
Q
Immunotherapy for Cancer
A
- prophylactic vaccines against liver and cervical cancer are available
- HPV and HBV vaccines protect against some cancers…Trastumab (Herceptin) consists of monoclonal antibodies aginast a breast cancer growth factor
- immunotoxins are chemical poisons linked to monoclonal antibody; the antibody selectivity locates the cancer cell for release of the poison
12
Q
Immunodefiencies:
A
- immunodeficienceis can be congenital or acquired
- congenital immunodeficienvies are due to defect or absent genes
- a variety of drugs, cancerns, and infectious disease can cause acquired immunodeficiencies
13
Q
Acquired Immunodeficiency Syndrome (AIDS):
A
-the origin of AIDS: HIV is thought to have originated in African and was brought to other countries by modern transportation and unsafe sexual practices
HIV Infection:
- AIDS is the final stage of HIV infection
- HIV is a retrovirus with single-stranded RNA, reverse transciptase, and a phospholipid envelop with 120 spikes
- HIV spikes attach to CD4 and coreceptors on host cells; the CD4 receptor is found on T helper cells, macrophages, and dendritic cells
- viral RNA is transcribed to DNA by reverse transciptaste. The viral DNA becomes integrated into the host chromosome to direct synthesis of new viruses or to remain latent as a provirus
- HIV evades the immune system in latency, in vacuoles, by using cell-cell fusion, and by antigenic change
- HIV infection is categorized by clinical phases: phase 1 (asymptomatic), phase 2 (indicator opportunistic infections), and phase 3 (CD4+ cells < 200 cells/ul)
- the progression from HIV infection to AIDS takes about 10 years
- the life of an AIDS patient can be prolonged by the proper treatment of opportunistic infections
- long-term survivors and elite controllers may hold the key to HIV treatment
14
Q
Diagnostic Methods
A
- HIV antibodies are detected by ELISA and Western Blotting
- Plasma viral load tests detect nucleic acid and are used to quantify HIV in blood
15
Q
HIV Transmission:
A
- HIV is transmitted by sexual contact, breast milk, contaminated needles, transplacental infection, artificial insemination, and blood transfusion
- in developed countries, blood transfusions are not a likely source of infection because blood is tested for HIV antibodies
16
Q
AIDS Worldwide:
A
-heterosexual intercourse is the primary method of HIV transmission
17
Q
Preventing and Treating AIDS:
A
- transmission can be reduced by biomedical, behavioral, and structural interventions
- current chemotherapeutic agents target cell entry and the virus enzymes, including reverse transcriptaste, integraase, and protease
- vaccine development is difficult because there are different antigenic clades and the virus remains inside host clels
Microbiology Exam #3
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