Chapter 43 Section 1

Animals are constantly under attack by __, infectious agents thta cause disease.
Defenses make up an __, which enables an animal to avoid or limit many infections.

An animal's most basic defense against __ is a barrier. An outer covering, like skin or a shell, provides a sigificant obstacle to invasionn by the microbes that re present on the body.
An immune system must carry out __, distinguishing nonself from self.

In identifying pathogens, animal __ use receptors that specifically bind molecuels from foreign cells or viruses. THere rae two general strategies for such molecular recognition, each forming the basis for a particualr system for immunity.

o One defense system, __, is found in all animals.

__ responses are active immediately upon infection and are the same whether or not hte pathogen ahs been encountered previously. __ icludes the barrer defenses (like skin) as well as defeness that combat pathogens after they enter the body. The activation of many o these internal defenses relies on recognition of pathogens. __ cells produce a small preset group of receptor proteins that accomplish this task. Each __ receptor binds a molecule or structure that is absent from animal bodies but is common to a large class of microbes. In this way, __ systems detect a very broad range of pathogens.

A second defense system, found only in vertebrates, is __, also known as __. __ responses are activated after after innate immune defenses take effect and develop more slowly. The name acquired reflects the fact that this immune response is enhanced by previous exposure to the infecting pathogen.

Ex of acquired responsses: synthesis of proteins taht inactivate a bac toxin and the targeted killing of a virally infected body cell.

Animals with __ produce a large arsenal of receptors. Each acquired immune receptor recognizes a feature typically found only on a part part of a part moleucule in a particular microbe. Accordingly, an aacquired immune system detects pathogens with tremendous specificity.

TRUE OR FALSE:
Innate immune systems are found in all animals and plants. Invertebrate innate immunity does not reprel and fight infection with only this type of immune system.
True False

In vertebrates, _- serves both as an immediate defense against infection and as the foundation for __ defenses.

Insects rely on their __ as a first line of defense against infection. Composed largely of the polysacccharide __, teh exoskeleeton provides an effective barrier defense against most pathogens. A chitin-based barrier is also present in the insect inteestine, where it blocks infection by many microbes ingested with food.
__, an enzyme that digests microbial cell walls, and a low pH further protect the insect digestive system.

Any pathogen that breaches an insect's barrier defenses encounters a number of internal immune defenses. Immune cells called __ circulate withi the __, the insect equivalent of blood.

SOme __ carrry out a cellular defense called __, igestion and digestion of bacteria and other foreign substances. OTher __ trigger the production of chems that kill microbes and help entrap multicellular parasites. Encounters with pathogens in the __ also cause hemocytes and certain other cells to secrete __.

The __ circulate throughout the body of the insect and inactivate or kill fungi and bacteria by disrupting their plasma membranes.

True or False:
In recognizing foreign cells, immmune response cells of insects rely on unique molecules in the outer layers of fungi and bacteria. Fungal cell walls contain certain unique polysaccharides, while bacterial cell walls contain certain unique polysaccharides, while bacterial cell walls have polymers containg combos of sugars and amino acids not found in animal cells. Such macromoleucles serve as identity tags in the prcesss of pathogen recognition. Insect immune cells secrete specialized recognition proteins, each of which binds to the macromolecule specific to a particular type of fungus or bacterium.
True False

True or False:
Immune responses are distinct for different clases of pathogens.
True False

True or False:
In vertebrates, innate immune defenses coexist with the mreo recently evolved system of acquired immunity.
True False

In mammals, __ block the entry of many pathogens. THese barrier defenses include not only the skin but also the mucous membrane slining the __, __, __ and __ tracts. Certain cells of the mucous membranes produce __, a viscous fluid that enhances defenses by trapping microbes and other particles.

In the __, ciliated epithelial cells sweep mucus and any entrapped microbes upward, helping preven infection of hte lungs.
- __, __, and __ that bathe various exposed epithelia provide a washing action that also inhibits colonization by microbes.

Beyond their physical role in inibiting microbe entry, body secretions create an enironment that is hostile to many microbes. __ in saliva, mucous secretions, and __ destroys susceptible bacteria as they enter the upper respiratory tract or the openings around the eyes. Microbes in food or water and those in swallowed mucus must also contend with the acidic environment of the stomach, whicl kills most microorganisms before they can enter the intestines. Similarly, secretions from __ (oil) glands and sweat glands give human skin a pH ranging from 3 to 5, acidic enough to prevent the growth of many microorganisms.

Pathogens that make their way into the body are subject to detection by phagocytic WBCs (__). These cells recognize microbes using receptors that are very similar to the Toll receptor of insects.

Eacch mammalian __ recognizes fragments of molecules characteristic of a set of pathogens.
- In each case, the recognized macromolecule is normally absent from the vertebrate body and is an essential component of a class of microbes.

As in insects, recognition by a __ triggers a series of internal defenses, beginning with __. A WBC recognizes and engulfs invading microbes, trapping them in a vacuole. The vacuole then fuses with a lysosome, leading to destruction of the microbes in two ways.
First, __ and other gases produced in the lysosome poison the engulfed microbes.
Second, __ and other enzymes degrade microbial components.

The most abundant phagocytic cells in the mammalian body are __. Signals from infected tissues attract __, which then engulf and destroy microbes.

__ (big eaters) provide an even more effective phagocytic defense. Some of these large phagocytic cells migrate throughout the body, while others reside permanently in various organs and tissues. __ in the spleen, lymph nodes, and other tissues of the lymphatic system are particularly well positioned to combat pathogens.

Microbes in the blood become trapped in the spleen, whereas microbes in interstitial fluid flow into lymph and are trapped in __. In either location, they encounter, they encounter resident __.

Two other types of phagoctyes- __ and __ play more limited roles in innate defense.

__ have low phagocytic activity but are important in defending against multicellular invaders, such as parasitic worms. Rather than engulfing such parasites, __ position themselves against the parasite's body and then discharge destructive enzymes that damage the invader.

__ populate tissues that are in contact with the environment. They mainly stimulate development of acquired immunity against microbes they encounter.

Pathogen recogntition in mammals triggers hte production and release of a variety of peptides and proteins that attack microbes or impede their reproduction. Some of these defense molecules function like the antimicrobial peptides of insects, damaging broad groups of pathogens by disrupting membrane integrity. Others, including the __ and __ proteins, are unique to vertebrate immune systems.

__ are proteins that provide innate defense against viral infections. virus-infected body cells secrete __, inducing nearby uninfected cells to produce substances htat inhibit viral reproduction. In this way, __ limit teh cell-to-cell spread of viruses in the body, helping control viral infections like colds and influenza. SOme WBCs secrete a different type of __ that helps activate macrophages, enhancing their phagocytic ability. Pharmaceutical companies now mass-produce __ by recombinant DNA technology for treating certain viral infections, like hep C.

tHE __ CONSISTS OF ROUGHLY 30 PROTEINS IN BLOOD PLASMA THAT FUNCITON TOGETHER To fight infections. These proteins circulate in an inactie state and are activated by substances on the surface of many microbes. Activation results in a cascade of biochemical reactions leading to __ (bursting) of invading cells. The __ also functions in inflammation, as well as in the acquired defenses.

THe pain and swelling that alert you to a splinter under your skin are the result of a local __, the changes brought about by signaling moelcules released upon injury or infection.

One important inflammatory signaling molecule is __, which is stored in __, connective tissue cells that store chemicals in granuels for secretion. __ released by mast cells at sites of tissue damage triggers nearby blood vessels to dilate and become more permeable. Activated __ and other cells discharge additional signaling molecules that further promote blood flow to the injured site. THe resulting increase in local blood supply causes the redness and heat typical inflammation. Capillaries engorged with blood leak fluid into neighboring tissues, causing __.

During innflammation, cycles of signaling and response transform the infection site. Enhanced blood flow to the injury site helps deliver antimicrobial proteins. Activated __ proteins promote further release of __ and help attract phagocytes. Nearby endothelial cells secrete signaling molecules that attract __ and __. Taking advantage of increased vessel permeability to enter injured tissues, these cells carry out additional phagocytosis and inactivation of microbes. The result is an accumulation of __, a fluid rich in WBCs, dead microbes and cell debris.

A mino injury causes local inflammation, but severe tissue damage or infection may lead to a response that is __ (throughout the body)- such as an incrased production of WBCs. Cells in injured or infected tissue often secrete molecuels that stimulate the release of additional __ from the bone marrow. In a severe infection, like meningitis or appendicitis, the number of WBCs in the blood may increase several fold within a few hours.

Another systemic inflammatory response is __. Some toxins produced by pathogens, as wella s substances called __ released by activated macrophages, can reset the body's thermostat to a higher temp. The benefits of the resulting fever are still a subject of debate. One hypothesis is that an elevated body temp may enhance phagocytosis and by speeding up chemical reactions, accelerate tissue repair.

Certain bacterial infections can induce an overwhelming systemic inflammatory response, leading to alife-threatenign condition called __. Characterized by very high fever, low blood flow, and low blood pressure, __ occurs most often in the very old and the very young. It is fatal in more than one-third of cases.

__ help recognize and eliminate certain diseased cells in vertebrates. With the exception of RBCs, all cells in the body normally have on their surface a protein called a __ moecule. Following viral infection or conversion to a cancerous state, cells sometimes stop expressing this protein. The __ cells that patrol the body attach to such stricken cells and release chemicals that lead to cell death, inhibiting further spread of hte virus or cancer.

Adaptatiosn have evolved in some pathogens that enable them to avoid destruction by phagocytic cells. Among bacteria that do not avoid recognitoin, some are resistant to breakdown within lysosomes following __
- These and other mechanisms that prevent destructin by the __ make the microbes that psosess them substantial pathogenic threats: TB kills more than a mil people a year worldwide.