The Biology of Cancer

Definitions and Concepts

Antibody-Mediated Cell Cytoxicity

Antibodies produced by B-Cells:

• Bind and neutralize antigens
• Coat and atrract components which lyse the membrane of a foreign invader such as a bacteria
• Coat and attract phagocytes which break down the antigen

Antigen

a foreign material in the body

Cell-Mediated Immunity

Performed by T-Cells. Major Histocompatability Complex Protein (MHC) molecules in normal, macrophage, and B-cells bringe peptides to the surface of the cell. T-Cells then manage the disposal of the foreign agent. All cells contain MHC I, but only B-Cells and Antigen Presenting Cells (Macrophages and Dendritic Cells) contain MHC II. Examples:

• A normal cell infected with a virus will use MHC I to carry viral peptides to the surface of the cell. There, they can be detected by Killer T cells which secrete cytotoxins to kill the infected cell.
• A Macrophage can house infectious particles such as bacteria in their vesicles. MHC II brings peptides from these vesicles to the cell surface. Infected macrophages will also produces a protein called B7. Inflammatory T-Cells detect these two signals and respond by stimulating the Macrophage to destroy the material in its vesicles.
• B-cells have antibodies on their surface which bind to antigens in the bloodstream. The antigen is taken into the cell in a vesicle and broken down into peptides. MHC II brings the peptide to the cell's surface where a helper T-cell idetects the foreign peptide and stimulates the B-Cell to produce more antibodies to that antigen.

Costimulation

A second signalling molecule, B7, must be present on the cell membrane of the presenting cell for Cell-Mediated Immunity to occur. One possible reason for the failure of the immune system to supress emerging tumors is the loss or inactivation through mutation of the gene which codes for B7 would allow tumor cells to escape the control of cell-mediated immunity.

Exogenous

(viral genes) Gene sequences not found in the host organism: derived elsewhere

Immunity

a response to an antigen

Immunological Tolerance

failure of organism to mount an immune attack against a specific antigen

In Vitro

in cell culture

In Vivo

in a living host

Lymphocyte

a class of white blood cells which are responsible for immune specificity

LTR

The ends of a viral genome, which contains regulatory information, usually directing that the viral genes be expressed at a very high level

Metastasis

The process by which cancer spreads from one organ of the body to another

Oncogene

One of a large number of tgenes that can help make a cell cancerous. Typically, a mutant form of a normal gene (proto-oncogene) involved in the control of cell growth or division. The viral form of an oncogene is usually referred to as 'v-onc'

Proto-Oncogene

Normal gene, usually concerned with the regulation of cell proliferation, that can be converted into a cancer-promoting oncogene by mutation. The normal celluarform of a proto-oncogene is usually referred to as 'c-onc'

Virus

entities whose genomes are elements of nucleic acid that replicate inside living cells using the cellular synthetic machinery, and cause the synthesis of specialised elements [virions] that can transfer the genome to other cells