Nonself antigen: abnormal proteins found in infected or abnormal cellMHC Proteins and Antigen Presentation (cont.)Class II MHC proteinsBind with longer fragments (14–17 amino acids) of exogenous (extracellular) antigens that have been engulfed and broken down in a phagolysosome by antigen-presenting cellClass II MHC proteins recognized by helper T cellsActivation and Differentiation of T cells T cells can be activated only when antigen is presented to themActivation is a two-step process1.Antigen binding2.Co-stimulationBoth occur on surface of same APCBoth are required for T cell activationCytokines - Chemical messengers of immune systemoInterleukin 1(IL-1) is released by macrophages and stimulates T cells to:Release interleukin 2 (IL-2)Synthesize more IL-2 receptorsoInterleukin 2 (IL-2) is a key growth factor, acting on same cells that release it and other T cellsEncourages activated T cells to divide rapidlySection 21.7– Insufficient or overactive immune responses create problems13
AIDS (Acquired Immune Deficiency Syndrome)AIDS was first identified in this country in 1981. The Center for Disease Control in Atlanta was receiving reports of abnormally high numbers of Pneumocystis pneumonia, a rare type of pneumonia caused by a protozoan and Kaposi’s sarcoma, a cancer of the blood vessels seen as purple lesions on the skin, usually only in elderly men, occurring in young homosexual males. After a lot of investigation, it was discovered that these 2 diseases were actually OPPORTUNISITIC INFECTIONS of a deteriorating immune system. The agent that causes AIDS is HIV, Human Immunodeficiency Virus.HIV is a fragile virus, unable to live long outside of a host’s body. It is transmitted in body secretions – blood, semen, vaginal fluids, and also found in tears and saliva. The virus commonlyenters the body via blood transfusions of contaminated blood, contaminated needles and during intimate sexual contact in which the mucosa is torn or where there are open lesions.This includesvaginal and anal intercourse, oral sex, sharing contaminated needles, tainted blood transfusions, infection in uterofrom infected mother and breast feeding.Some of the types of cells that the HIV can enter are Helper T cells, macrophages and brain cells. When Helper Ts (T4s) are invaded, the population decreases, leading to a collapse of the immune system and, for the patient, death usually by an opportunistic disease like cancer, pneumonia or a raging infection.Symptoms become evident at different time intervals from exposure, depending upon the individual’s health and the strain of the virus. Usually, symptoms such as opportunistic infections, night sweats, swollen glands, weight loss occurs within a few months to ten years after diagnosis.It is estimated that 5% of infected individuals are “nonprogressors” – people who have been infected with HIV but who, after at least 10 - 15 years, show no clinical signs of the disease.
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- Fall '16
- Lambrini Nicopoulos