Tumour immunology - ‫بسم اللة الرحمن‬...

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Unformatted text preview: ‫بسم اللة الرحمن‬ ‫الرحيم‬ Tumor immunology Tumor immunology Tumor immunology Tumor * Pathological cell masses derived by abnormal and uncontrollable clonal expansion of single cell * Transformation of normal cells to malignant cells by: a­ Spontaneous mutation during daily cell division chemical carcinogens b­ It may be induced by physical carcinogens viruses * Cells become antigenically different from normal cells * They are recognized and destroyed by immune system Etiology Of Tumor Etiology 1) Inherited : Expression of inherited oncogene e.g. viral gene incorporated into host gene 2) Viral: ­ Human papilloma, herpes type 2, HBV, EBV (DNA) ­ Human T­cell leuckemia virus (RNA) 3) Chemical: ­ Poly cyclic hydrocarbons cause sarcomas ­ Aromatic amines cause mammary carcinoma ­ Alkyl nitroso amines cause hepatoma 4) Radiological: Ultraviolet & ionizing irradiation 5) Spontaneous: failure in the cellular growth control Tumor Associated Antigens Tumor !) Viral Antigen : a­ Viral proteins and glycoproteins b­ New antigens produced by virally infected host cells under control of viral nucleic acid 2) Tumor specific antigens : ­ Tumor cells develop new antigen specific to their carcinogens 3) Tumor specific transplantation antigens : ­ Tumor cells express new MHC antigens due to alteration of normally present MHC antigens Tumor Associated Antigens Tumor 4) Oncofetal antigens: a­ Carcino­embryonic antigens (CEA) ­ Normally expressed during fetal life on fetal gut ­ Reappearance in adult life: GIT, pancreas, biliary system and cancer breast b­ Alpha fetoprotein: ­ Normally expressed in fetal life ­ Reappearance in adult life; hepatoma Immune Surveillance System Immune * During neoplastic transformation, new antigen develop * The host recognize them as nonself antigens * Cell mediated immune reactions attack these nonself tumor cells * Immune response act as surveillance system to detect and eliminate newly arising neoplastic cells Immune Surveillance System Immune This system include : 1) Natural killer (NK) cells They kill directly tumor cells,helped by interferon, IL­2 2) Cytotoxic T­cells They also kill directly tumor cells 3) Cell mediated T­cells (effector T­cells) They produce and release a variety of lymphokines : a­Macrophage activation factor that activate macrophag b­Gamma interferon and interleukin­2 that activate NK c­Tumor necrosis factor (cachectine) Immune Surveillance System Immune 4) B­cells : ­ Tumor associated antigens stimulate production of specific antibodies by host B­cells ­ These specific antibodies bind together on tumor cell surface leading to destruction of tumor through: a­ Antibody mediated­cytotoxicity : kill Cytotoxic T­cells IgG­coated tumor cells b­ Activation of macrophages release Sensitized T­cells macrophage activating factor IgG­coated tumor cells macrophages activate c­ Activation of classical pathway of complement leading to Lysis of tumor cells Tumor Escape Tumor Mechanisms by which tumor escape immune defenses: 1) Reduced levels or absence of MHCI molecule on tumor so that they can not be recognized by CTLs 2) Some tumors stop expressing the antigens These tumors are called “antigen loss variants” 3) Production of immunosuppressive factors by tumor e.g. transforming growth factor (TGF­β) 4) Tumor antigens may induce specific immunologic tolerance Tumor Escape Tumor 5) Tumor cells have an inherent defect in antigen processing and presentation 6) Blocking of receptors on T­cells by specific antigen antibodies complex (after shedding of tumor Ag) prevents them from recognizing and attacking tumor cells 7) Antigens on the surface of tumors may be masked by sialic acid­containing mucopolysaccharides 8) Immune suppression of the host as in transplant patients who show a higher incidence of malignancy Tumor Markers Tumor * Tumor markers : Tumor antigens * They are either or Tumor products (enzymes and hormones) * Tumor products are released in the serum of patients * They are used to confirm diagnosis and follow up the response to therapy Tumor Antigens Tumor 1) Alpha fetoprotein antigen (AFP) in cases of hepatoma 2) Carcinoembryoinic antigen (CEA) in gastrointestinal tumors, tumors of biliary system and cancer breast 3) Cancer antigen 125 (CA 125) in ovarian carcinoma 4) Cancer antigen 15­3 (CA15­3) in breast cancer 5) Cancer antigen 19­9 in colon and pancreatic tumor 6) Prostatic specific antigen (PSA) in prostatic tumors Tumor Products Tumor a) Hormones : ­ Human chorionic gonadotrophins (HCG) are secreted in cases of choriocarcinoma ­ Thyroxin (T3 & T4) is secreted in cases of cancer of thyroid gland b) Enzymes : ­ Acid phosphatase enzymes in cases of cancer prostae ­ Alkaline phosphatese, lipase and amylase enzymes in cases of cancer pancreas Thanks Thanks ...
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