Cell recognition and the Immune System Flashcards
What are the 2 defence mechanisms in the body?
Non-specific:
- They are immediate and are the same for all pathogens.
- They include physical barriers and phagocytosis since the phagocyte detects any non-self cell and destroys it.
Specific:
- They are slower and specific for each pathogen.
- They include lymphocytes in the cell mediated and humoral response.
What is an antigen?
A molecule that triggers an immune response by lymphocytes.
How is a lymphocyte able to distinguish between a self and non-self cell?
The proteins on the surface of the cell can be specific and have different tertiary structure.
What is a phagocyte?
A type of white blood cell called a macrophage that carries out phagocytosis
Where are phagocytes found?
In the blood and tissues
What is phagocytosis?
The process where cells engulf pathogens to form a vesicle or a vacuole.
Describe the process of phagocytosis.
- Phagocytes in the blood and tissue will be attracted to any chemical debris released by pathogens and move towards them
- The receptor binding points on the phagocytes will attach to the antigens on the pathogen via these receptors.
- The phagocyte changes shape to engulf the pathogen and contains it inside a phagosome vesicle
- A lysosome within the phagocyte will fuse with the phagosome and release its contents
- The lysozyme enzyme is released into the phagosome which hydrolyses the pathogen. This destroys the pathogen
- The soluble products are absorbed and used by the phagocyte. The antigen is placed on the cell surface membrane so the phagocyte becomes an antigen presenting cell.
What are T lymphocytes?
White blood cells involved in the specific immune system
Where are T lymphocytes made?
Made in the bone marrow but mature in the thymus
What are the two types of lymphocytes?
T lymphocytes and B lymphocytes
Where are B lymphocytes made?
Made and mature in the bone marrow
What processes are B and T lymphocytes associated in?
T lymphocytes - Cellular response
B lymphocytes - Humoral response
What is an antigen presenting cell?
Any cell that presents a non-self antigen on its surface
Why is the process called cell-mediated response?
The t cells only respond to the antigens that are presented on the antigen presenting cell
Describe the process of the cell-mediated response.
- Once a pathogen has been engulfed by a phagocyte, the antigen is placed on the cell surface and an antigen presenting cell is formed
- Helper T-cells have receptors on their surface which can attach to the antigens on the APC
- Once attached, it activates the helper t cells to divide by mitosis in order to replicate and make clones
- The cloned t helper cells differentiate into different cells.
- Some of them will remain as t helper cell and activate b lymphocytes
- Some stimulate macrophages to perform more phagocytosis
- Some become memory cells for the particular shaped antigen
- Some become cytotoxic T cells (killer t-cells)
What do cytotoxic T cells do and how?
They destroy abnormal or infected cells by releasing a protein called perforin which embeds inside the cell surface membrane and makes a pore allowing any substances to enter or leave which causes cell death.
What is a monoclonal antibody?
An antibody produced from identical B cells
Give one example of using monoclonal antibodies in a medical treatment.
Binds to specific antigens
Explain direct monoclonal antibody therapy.
- Some cancer is treated using monoclonal antibodies that have binding sites complementary in shape to the antigens on the cancer cell.
- The antibodies are given to the cancer patient and they bind onto the antigens on the cancer which prevents the cancer cell from growing.
Explain indirect monoclonal antibody therapy.
- Some cancer can be treated using monoclonal antibodies that have binding sites complementary in shape to the antigens on the cancer cells and have drugs attached to them.
- The cancer drugs are delivered directly to the cancer cells to kill them
Explain the humoral response.
- A B-cell is triggered when it encounters its matching antigen
- The B-cell engulfs the antigen and digests it and displays antigen fragments bound to MHC molecules.
- This attracts a matching mature Helper T-cell that will activate the B-cell to go through clonal expansion
- B-cells then undergo mitosis to form either plasma cells or memory B cells.
- Plasma cells make antibodies
- Memory B cells can divide rapidly into plasma cells when re-infected with the same pathogen to make large numbers of antibodies rapidly.
Describe the structure of HIV
- The core consists of RNA and reverse transcriptase
- Capsid is the outer protein coat
- The lipid envelope is an extra outer layer made out of membrane taken from the hosts cell membrane
- The attachment proteins are on the exterior of the envelope.
What is the function of attachment proteins in HIV?
Enables the virus to attach to the hosts helper t cell
How does HIV replicate?
- HIV is transported around the blood until it attaches to a CD4 protein on the Helper T-cells
- The HIV protein capsule will fuse with the Helper T-cell membrane which allows RNA and reverse transcriptase from the HIV to enter.
- Reverse transcriptase converts RNA into a DNA which moves into the Helper T-cells nucleus.
- The DNA is transcribed into mRNA and the Helper T-cells produce viral proteins from the mRNA to make new viral particles which destroys the Helper T-cells. These viral particles are then assembled and release from the cell.
