Immune System Quiz

1

.     Provides an immediate nonspecific immune response

Nonspecific immune system provides immediate defense against infection. However, it does not confer long-lasting or protective immunity to the host. Inflammation is one of the first responses of the immune system to infection or irritation. Inflammation is stimulated by chemical factors released by injured cells and serves to establish a physical barrier against the spread of infection, and to promote healing of any damaged tissue following the clearance of pathogens. The cells involved in inflammation include macrophages, dendritic cells, histiocytes, Kupffer cells, and mastocytes. Phagocytes are able to kill viruses by eating antigens and sending them to lysosomes, where enzymes and acids can digest the particle or organism.

Macrophage has receptor on its surface and then the receptor triggers the macrophage to engulf the antigen. Dendritic cells are mainly in the skin. The skin is usually the most common area to be in touch with bacteria or virus. Some of them remain at the skin because dendritic cells prevent them from being permeated.

2.     Activates T and B cells in response to an infection

The B lymphocytes are made in the bone marrows. They are responsible for the humoral response. A B cell is triggered when a matching antigen attaches to it. The B cell engulfs the antigen and digests it. After digestion, the B cell displays antigen fragments bound to its unique MHC (Major histocompatibility complex)

molecules. The combination of antigen and MHC brings in the help of a matching T cell with the presence of a protein CD4+. Cytokines produced by the T cell help the B cell to reproduce and grow into antibody. The antibodies are then released into the blood and match onto antigens.

T cells are released from the thymus. They are mobilized to help B cells that have already digested the antigen with the MHC combination. T cells are matured by the cytokines. Some T cells become helper cells that secrete cytokines to attract macrophages and other lymphocytes. Some T cells become cytotoxic cells and track down infected cells. Some cytokines produce more T cells.

3.     Responds to a later exposure to the same infectious agent

When the antigen enters the body, the responding naive B cells (ones that have never been exposed to the antigen) undergo clonal selection to produce a colony of cells that are specific for the antigen. Most of the cloned B cells differentiate into the plasma cells. The rest become memory B cells, which will survive for an average of ten years. The antibody molecules on a clone have unique paratope (the sequence of amino acids that binds to the epitope on an antigen.) Over many years, when the same antigen invades, the paratope, which match the antigen, will proliferate and have a better affinity for the antigen, thus killing the antigen faster than the first time.

The memory T cells work in similar mechanism. Memory T cells are also known as potentially cancer-fighting cells. They can recognize foreign invaders and cancer cells. Their function follows the principle of vaccination, which helps phagocytes to kill the antigen faster than the first time the person is vaccinated.

4.     Distinguishes self from nonself

Almost all of our body molecules are distinctive to our body. Therefore, they identify themselves as the master of the body. When a foreign invader enters our body, our antibodies will recognize them as hostile and will attack them. Usually, the method for body cells to distinguish from each other is by the molecule’s epitope. Epitope means the characteristic shape of a molecule. Most antigens, even the simplest microbes, carry several different kinds of epitopes on their surface; some may carry several hundred. If the marker on the antigen matches with the site on an antibody molecule, the antibody will bind to the antigen and activate other phagocytes to digest the antigen. In abnormal situations, the immune system can wrongly identify self as nonself and start a unnecessary immune attack. In some people, an apparently harmless substance such as ragweed pollen or cat hair can provoke the immune system to set off the inappropriate and harmful response known as allergy; in these cases the antigens are known as allergens.