Animals have to defend themselves against many potentially dangerous viruses, bacteria, and other pathogens it encounters.
These pathogens can be in the air, in food, and in water.
There are two ways they can counter these threats, with Innate Immunity (nonspecific), or Acquired Immunity (specific).
Lymphocytes are colorless cells found in blood, constituting approximately 25 percent of white blood cells and including B cells, which function in humoral immunity, and T cells, which function in cellular immunity.
Antibodies are defense proteins. Y-shaped protein on the surface of B cells that is secreted into the blood or lymph in response to an antigenic stimulus
Innate Immunity An Innate Immunity is an immunity that occurs naturally as a result of a person's genetic constitution. Innate immunities defend in a nonspecific way. Innate immunity is composed of two kinds of defenses, external and internal defenses . The external defenses include our skin, mucous and secretions. Bacteria and viruses cannot enter through the skin, meaning the skin works as a barrier. Mucous traps bacteria and expel them through the nose. Secretions, such as saliva and tears contain enzymes that kill bacteria. The Mucous traps microbes and the cilia expels mucous containing microbes upward into the pharynx. Mucus-producing cells (orange) Cilia (yellow) Tears and Saliva contain lysozyme, which is an enzyme that digests cell walls of many bacteria. The skin blocks bacteria and viruses from entering our bodies.
Internal Defenses and Chemical Defenses
Internal Defenses are divided into four different kinds: Phagocytic cells, Antimicrobial proteins, Inflammatory response, and Natural Killer Cells.
Phagocytic cells attach to their prey through surface receptors that bind to microorganisms. Four types of Phagocytic cells are:
-Neutrophils enter infected tissue, engulfing and destroying microbes.
-Macrophages engulf and destroy bacteria. They are an important class of antigen presenting cells.
-Eosinophils are critical defense against multicellular parasitic invaders.
-Dendritic Cells ingest microbes like macrophages do.
Antimicrobial Proteins help antibodies clear pathogens or mark them for destruction by other cells.
Inflammatory Response happens when there has been an entry of pathogens. These process occur during an inflammatory response, Histamine is released from mast cells, triggers dilation and increases permeability of nearby capillaries. Increased blood supply at the site which causes the redness and heat typical of inflammation.
Natural Killer Cells (NK) patrol the body and attack virus-infected body cells and cancer cells.
This image shows the process of
Phagocytosis and steps in how
this process happens.
When Pathogens enter the body, phagocytic cells rush to the injured site, and perform Phagocytosis.
An Acquired Immunity is the immunity that is developed from antibodies in an exposure to antigens, as from vaccination or an infectious disease. One can also obtain antibodies from the mother through the placenta.
Vaccines are weakened or killed pathogens, such as a virus or bacterium, that are inserted into the body to stimulate antibody production against certain pathogen inserted. Pathogens and bacterium inserted are incapable of causing severe infections.
Invertebrate Immune Mechanisms
Invertebrates have effective innate defenses and acquired immunities.
Invertebrates are mostly dependant on nonspecific mechanisms, such as innate defenses.
Examples of effective innate defenses are insects, they have hemolymph, which is equivalent to blood, hemolymph contain hemocytes which ingest bacteria by phagocytosis.
Examples of acquired immunity are Earthworms, phagocytic cells in a worm attack a second graft from the same donor worm much faster than the first graft. Most invertebrates exhibit no such immunological memory.
Role of the lymphatic system The lymphatic system produces and transports lymph fluid from tissues to the circulatory How does it aid in immunity? The lymphatic system produces lymphocytes which fights foreign molecules in the body .
Lymphocytes in acquired immunity
2 types of lymphocytes:
B lymphocytes (B cells)
Lymphocytes that are developed in the bone marrow. They recognize intact antigens only
2) T lymphocytes (T cells)
Lymphocytes that are developed in the thymus. They recognize small fragments of antigens that are bound to MHC molecules
What is an antigen?
Any foreign molecule that is specifically recognized by lymphocytes and elicits a response from them.
Generation of diversity by gene rearrangement : At an early stage, the lymphocyte contains a series of variable V gene segments separated by a LONG stretch of DNA., the light chain is not functional. When a set of enzymes called recomvinase links one V gene segment to one J gene segment, the long stretch is eliminated and becomes functional. This process is called V-J rearrangement. These chains combine with other chains to form B cell’s antigen receptors.
Testing & removal of self-reactive lymphocytes
Because a lymphocyte exists only to hunt down and destroy specific antigen molecules, when the antigens are already present in the body (and are not hazardous), the lymphocyte is no longer useful. Therefore, it is destroyed by apoptosis or rendered nonfunctional— so that only lymphocytes that react to foreign molecules remain.
Clonal selection of lymphocytes
Because lymphocytes are only made for specific antigens, only a very few # of lymphocytes bear receptors specific for the intruding antigen. So they clone themselves infinitely many times. This allows them to destroy the antigen more effectively.
Major Histocompatibility complex (MHC)
MHC molecules = cell-surface proteins
What do they do?
They bind peptides derived from foreign antigens in the body
* Some of the MHC are called “ antigen-presenting molecules ” because they play a key role in displaying internalized antigens to helper T cells.
Ex. Macrophages, B cells
Humoral immune response – B cells are activated and go through clonal selection, resulting in the increased production of antibodies that circulate the blood and lymph
Cell-mediated immune response – cytotoxic T cells are activated and go through clonal selection, which then travel directly to the target cells to destroy them
Helper T cell – responds to antigens displayed by antigen-presenting cells and stimulates the activation of nearby B and cytotoxic T cells
Helper T Cells
Helper T cells respond to nearly all antigens – When a helper T cell encounters and recognizes a class II MHC molecule-antigen complex on an antigen presenting cell the helper T cell proliferates and differentiates into a clone of activated helper and memory helper T cells. The surface protein CD4 of helper T cells bind the class II MHC molecule that helps with the activation of the helper T cell. Helper T cells release cytokines, which promote both cell-mediated and humoral responses.
More Types of Cells
Dendritic cells (picture probably needed) engulf and degrade bacterium and displays the bacterial antigen fragments that also activate helper T cells.
Cytotoxic T cells (picture needed)– these cells destroy body cells infected by viruses or other pathogens as well as cancer and transplanted cells. Fragments of non-self proteins created in such cells are associated with the class I MHC molecules and are displayed on the cell surfaces, where they can be recognized by the cytotoxic T cells. The surface protein CD8 on the cytotoxic T cell binds to the CD8 and enhances the activation of the cytotoxic T cell. When such a process is completed the cytotoxic T cell differentiates into an active killer. It secretes perforin molecules, which form pores in the target cell membrane, and proteolytic enzymes that enter the target cell which initiate apoptosis in the target cell. The cytotoxic T cell then detaches from the target cell and proceeds to hunt other infected cells. They can defend against malignant tumors in his way.
B cells – Activated helper T cells present antigen fragments to B cells, which activates it. B cells proliferate and differentiate into a clone of antibody-secreting plasma cells and a clone of memory B cells.
A microscopic view of a B Cell
Antibodies- Have 5 different classes, each has a unique structure. Antibodies aid in immunity using four different methods: Viral neutralization: antigens attach to antigens and block the antigens’ ability to bind to a host, also helps with phagocytosis. Agglutination: the pentamer-shaped antibody class binds to five antigens at once, increasing the effectiveness of phagocytosis. Precipitation: antibodies form long chains by binding to water-soluble antigens, also helps with phagocytosis. Activation of complement system and pore formation: antibodies bind to complement proteins and a foreign cell and the activated complement proteins generate a MAC (membrane attack complex) that forms a pore in the membrane. Ions and water rush in, causing the foreign cell to swell and then lyse.
Types of Immunities
Active immunity: immunity acquired by natural exposure to an infectious agent
Passive immunity: immunity acquired by transferring antibodies from a person with immunity to particular infectious agent to someone who is not.
Blood types (such as “A” or “B”) reflect the antigens present in the red blood cells.
Type A red blood cells will have anti-B antigens and type B will have anti-A antigens.
Type O has both anti-A and anti-B antigens, whereas type AB has neither.
One major issue with blood transfusions is that if the blood is of the wrong type(i.e. type A donated to type B) the host body will reject and attack the blood that has been introduced.
Organ and Tissue Transplants
Organ transplant compatability is based on similarity of major histocompatibility complex molecules between donor and recipient.
Medication that suppresses the immune response of the donor is used.
In bone marrow transplants there is a danger of the donated marrow attacking the host body due to the
Allergies are exaggerated responses to antigens called allergens
An allergen, such as pollen, will trigger a release of histamines from granules located within mast cells.
Histamine causes small blood vessels to dilate, which can in turn cause symptoms such as sneezing, runny nose, and watering of the eyes.
In the case of a severe allergic reaction, histamine release is triggered in a cascade that causes all of the blood vessels of the body to dilate, causing a potentially fatal drop in blood pressure, called anaphylactic shock.
A grain of pollen, a common allergen
There are two types of immunodeficiencies: Inborn (or Primary) immunodeficiencies Acquired (or Secondary) immunodeficiences
Inborn immunodeficiencies are present from birth, and can be the result of defects in the immune system or the cells that comprise it
Acquired Immunodeficiencies are acquired by exposure to external influences and pathogens, in addition to certain types of cancers.
Stress and depression can both cause the efficiency of the immune system to be hindered.
An HIV (Human Immunodeficiency syndrome) infection ultimately leads to a case of AIDS (acquired immunodef- iciency syndrome
The HIV virus operates by making use of proteins found in cells of the immune system. The virus specifically uses cells that have low levels of CD4 for infecting.
Once the cell is infected, the virus reverse transcribes its RNA, and the resulting DNA is integrated into the DNA of the host cell. This effectively creates a cell that can create more virus cells, but is not targeted by the immune system.
HIV cannot currently be stopped, but only slowed.
Anatomy of the HIV virus
AIDS is the autoimmune disease resulting from an infection of HIV
AIDS essentially destroys the immune system, which leaves the body weakened and vunerable to all sorts of pathogens and cancers.
AIDS is most often not the cause of death in AIDS patients. The diseases they are now susceptible to with their lack of an immune response makes even a slight infection or disease deadly.