lOMoARcPSD|255728 27
The Five Classes of Antibodies
▪
Antibodies also known as immunoglobulins (Ig) ▪ Classes of antibodies
– IgG: most prevalent in the blood
– IgM: first antibody produced in an immune response – IgA: found in body secretions, including
breast milk – IgD: function is unclear
– IgE: plays a key role in allergic responses
T Cells: Cell-Mediated Immunity
▪
T cells
– Originate from stem cells in the bone marrow – Mature in the thymus
▪
Types of T cells – CD4 T cells
– Helper T cells and memory T cells – CD8 T cells
– Cytotoxic T cell
Macrophages and B Cells Activate T Cells
▪
T cells must be presented with antigen by antigen- presenting cells (APCs)
▪
APCs include – Macrophages – B cells
T Cells: Cell-Mediated Immunity
▪
Helper T cells
•
– Secrete cytokines, which stimulate other immune
system cells
•
– Play a key role in directing the immune response
•
– Are targets of HIV infection
▪
Cytotoxic T cells
– Directly attack and destroy abnormal (tumor or viral-
infected) cells and foreign cells
lOMoARcPSD|255728 27
▪
Memory T cells
– Reactivate during later exposures
Immune Memory Creates Immunity
▪
Primary immune response
– Occurs on first exposure to antigen – Characteristics
– Lag time of 3–6 days for antibody production
– Peaks at 10–12 days
▪
Secondary immune response
– Occurs on second and subsequent exposure to antigen
– Characteristics
– Lag time is hours – Peaks in days
– Much more antibody produced
Medical Assistance in the War Against Pathogens
▪
Immunization
– A strategy for causing the body to develop immunity
to a specific pathogen
– Active immunization
– Intentionally expose individual to a form of the antigen
that doesn’t produce disease (vaccine) – Also known as vaccination
– Passive immunization
– Administer protective antibodies to an individual
Medical Assistance in the War Against Pathogens
▪
Monoclonal antibodies
– Specific antibodies produced in the laboratory by a
hybrid B cell clone
– Commercial applications of monoclonal antibodies
lOMoARcPSD|255728 27
– Home pregnancy tests
– Prostate cancer screening test
– Diagnostic testing for hepatitis, influenza, HIV
Medical Assistance in the War Against Pathogens
▪
Antibiotics combat bacteria
•
– Antibiotics kill bacteria or inhibit their growth
•
– Antibiotics are selectively toxic for bacteria by
targeting features of bacterial cells that are different
from eukaryotic cells
•
– Antibiotics are not effective against viruses
•
Tissue Rejection: A Medical Challenge
▪
Tissue rejection
– May occur following tissue or organ transplant if recipient’s immune system attacks
the transplanted tissue/organ
▪
To minimize risk of rejection
o – Must match ABO and other blood group antigens and
MHC antigens
o – 75% MHC match is essential
– MHC antigens allow body to distinguish “self” from “non-self”
o – Immunosuppressive drugs—prevent patient’s immune
system from attacking transplanted tissue
Inappropriate Immune System Activity Causes Problems
▪
Allergies are hypersensitivity reactions
•
– Inappropriate response to an allergen
lOMoARcPSD|255728 27
•
– Allergen: any substance (antigen) that causes an
allergic reaction (not a pathogen, but the body reacts
as though it is a pathogen)
•
– Examples of allergens
– Pollen
– Bee venom
– Foods (nuts, seafood)
– Oil from poison ivy plant
1. Inappropriate Immune System Activity Causes Problems
▪
Allergies (cont’d)
– Excessive inflammatory response mediated by
– IgE
– Basophils and mast cells – Histamine
– Reactions may be localized or systemic – Localized: affect only the area exposed –
Systemic: affect several organ systems
– Anaphylactic shock: severe life-threatening systemic reaction (difficulty breathing,
circulatory collapse, drop in blood pressure)
1. Inappropriate Immune System Activity Causes Problems
▪
Allergies (cont’d)
– Treatment of allergies
– Antihistamines—treatment of mild to moderate reactions
– Epinephrine injection—treatment of anaphylactic shock – Allergy shots
1. Inappropriate Immune System Activity Causes Problems
▪
Allergies (cont’d)
– Treatment of allergies
– Antihistamines—treatment of mild to moderate reactions
– Epinephrine injection—treatment of anaphylactic shock – Allergy shots
lOMoARcPSD|255728 27
Immune Deficiency: The Special Case of AIDS
•
▪ AIDS: Acquired Immune Deficiency Syndrome
•
▪ Caused by infection with HIV (Human
Immunodeficiency Virus)
•
▪ HIV targets helper T cells
•
▪ HIV attaches to CD4 receptors of helper T cell, and gains entry to the cell
•
▪ Transmission via body fluids (blood, semen, breast milk, vaginal secretions)
AIDS Develops Slowly
▪
Phase I
•
– May last a few weeks to a few years
•
– Brief period of flu-like symptoms
– Swollen lymph nodes – Chills
– Fever
– Fatigue
– Body aches
•
– Most people don’t exhibit recognizable symptoms
•
– Virus is multiplying, antibodies are made but are
ineffective for complete virus removal
1. AIDS Develops Slowly
▪
Phase II
– Occurs within 6 months to 10 years
– Characterized by opportunistic infections
– Helper T cells affected, numbers are decreasing
– If untreated, 95% will progress to next phase (AIDS)
1. AIDS Develops Slowly
lOMoARcPSD|255728 27
▪
Phase III: Clinical AIDS
– Helper T cells fall below 200 cells/mm3
– Opportunistic infections and cancers present
– Tuberculosis
– Pneumonia
– Meningitis
– Encephalitis
– Kaposi’s sarcoma
– Non-Hodgkins lymphoma
– If untreated, nearly always fatal
The AIDS Epidemic: A Global Health Issue
▪
Worldwide
– More than 35 million infected with HIV – 39 million dead so far
– Most infections in sub-Saharan Africa – Increasing spread in Asia and India
▪
United States
– 14,000 deaths/year
– >500,000 people living with AIDS in the United States
– Additional 700,000 infected individuals not yet symptomatic
Risky Behaviors Increase Your Chances of Getting AIDS
▪
Males (3/4 of cases)
– Sex with other men
– Sharing needles during intravenous drug use – Heterosexual sex with HIV-infected female
▪
Females (1/4 of cases)
– Sex with HIV-infected male
– Sharing needles during intravenous drug use
Making Sex Safer
▪
Abstinence
▪
Reduce number of sexual partners
▪
Choose sexual partners with low-risk behavior ▪ Avoid high-risk sexual practices
lOMoARcPSD|255728 27
– Anal-genital sex is a high-risk practice
▪
Use latex or polyurethane condoms or barriers ▪ Use nonoxynol-9 spermicide
▪
GET TESTED
New Treatments Offer Hope
•
▪ Mechanisms of anti-HIV drugs
o – Inhibition of entry of HIV into host cell (entry inhibitors)
o – Inhibition of enzymes required for replication of viral
RNA (reverse transcriptase inhibitors)
o – Prevention of insertion of viral genome into the cell’s
DNA (integrase inhibitors)
o – Inhibition of enzymes required to assemble viral
proteins (protease inhibitors)
•
▪ Early treatment with drug combinations may delay or
prevent clinical AIDS
•
▪ Vaccines: under development and testing
