¡¡¡¡Text 6

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¡¡¡¡The immune system is equal in complexity to the combined intricacies of the brain and nervous system. The success of the immune system in defending the body relies on a dynamic regulatory communications network consisting of millions of cells. Organized into sets and subsets, these cells pass information back and forth like clouds of bees swarming around a hive. The result is a sensitive system of checks and balances that produces an immune response that is prompt, appropriate, effective and self-limiting.

¡¡¡¡The heart of the immune system is the ability to distinguish between self and non-self. When immune defenders encounter cells or organisms carrying foreign of non-self molecules, the immune troops move quickly to eliminate the invaders. Virtually every body cell carries distinctive molecules that identify it as self. The body¡¯s immune defenses do not normally attack tissues that carry a self marker. Rather, the immune cells and other body cells coexist peaceably in a state known as self-tolerance. When a normally functioning immune system attacks a nonª²self molecule, the system has the ability to remember the specifics of the foreign body. Upon subsequent encounters with the same species of molecule, the immune system reacts accordingly. With the possible exception of antibodies passed during lactation, this so-called immune system memory is not inherited. Despite the occurrence of a virus in your family, your immune system must learn from experience with the many millions of distinctive nonª²self molecules in the sea of microbes in which we live, learning necessitates producing the appropriate molecules and cells to match up with and counteract each non-self invader.

¡¡¡¡Any substance capable of stimulating an immune response is called an antigen. Tissues or cells from another individual (except an identical twin, whose cells carry identical selfª²markers) act as antigens; because the immune system recognizes transplanted tissues as foreign, it rejects them. The body will even reject nourishing proteins unless they are first broken down by the digestive system into their primary, nonª²antigenic building blocks. An antigen announces its foreignness by means of intricate and characteristic shapes called epitomes, which stick out from its surface. Most antigens, even the simplest microbes, carry several different kinds of epitomes on their surface, some may even carry several hundred. Some epitomes will be more effective than others at stimulating an immune response. Only in abnormal situations does the immune system wrongly identify self as non-self and execute a misdirected immune attack.

¡¡¡¡The result can be so-called autoimmune disease. The painful side effects of those diseases are caused by a person¡¯s immune system actually attacking itself. (427 words)

¡¡¡¡1. We know from the passage that the immune system _______________

¡¡¡¡[A] is no less complicated than the nervous system.

¡¡¡¡[B] far exceeds the human brain in intricacy.

¡¡¡¡[C] is enclosed by numerous sensitive cells.

¡¡¡¡[D] results in an effective communications network.

¡¡¡¡2. The principal task of the immune system is to _______________

¡¡¡¡[A] recognize and eliminate all foreign molecules that enter the body.

¡¡¡¡[B] remove all the substances that invade the body organisms.

¡¡¡¡[C] defend the body from the attacks of different viruses and bacteria.

¡¡¡¡[D] identify and specify all nonª²self molecules it encounters.

¡¡¡¡3. The remembering power of a person¡¯s immune system is _______________

¡¡¡¡[A] mostly descended from his/her ancestors.

¡¡¡¡[B] partially passed down from his/her mother.

¡¡¡¡[C] mainly acquired through fighting against foreign cells.

¡¡¡¡[D] basically generated by its communications network.

¡¡¡¡4. Which of the following is NOT true according to the passage?

¡¡¡¡[A] A tissue transplanted from father to daughter would be less acceptable than that transplanted between twins.

¡¡¡¡[B] The immune system would never wrongly identify self as nonª²self and execute a misdirected immune attack.

¡¡¡¡[C] When a normally functioning immune system attacks a nonª²self molecule, the system will remember the specifics of the foreign body.

¡¡¡¡[D] The immune cells and other body cells can coexist peaceably in a state known as selfª²tolerance.

¡¡¡¡5. The main idea of the passage may be generalized as_______________

¡¡¡¡[A] the success of the immune system in distinguishing foreign substances.

¡¡¡¡[B] the normal and abnormal activities of the immune system in the body.

¡¡¡¡[C] the unfavorable effects of the immune system on organ transplantation.

¡¡¡¡[D] the essential duties of the immune system in guarding the body.

¡¡¡¡ºËÐÄ´Ê»ã

¡¡¡¡intricacy n. ´í×Û¸´ÔÓµÄÊÂÎï;·×·±ÄѶ®Ö®´¦

¡¡¡¡dynamic a. ¶¯Ì¬µÄ,Óж¯Á¦µÄ,ÓÐÁ¦µÄ

¡¡¡¡back and forthÀ´»ØµØ,·´¸´µØ

¡¡¡¡hive n. ·ä·¿,·äÏä

¡¡¡¡organism n. ÉúÎïÌå,ÓлúÌå

¡¡¡¡molecule n.·Ö×Ó

¡¡¡¡tissue n. (¶¯¡¢Ö²ÎïµÄ)×éÖ¯;±¡µÄɴ֯Ʒ

¡¡¡¡antigen n. ¿¹Ô­

¡¡¡¡epitome n. ÕªÒª,ËõÓ°,»¯Éí

¡¡¡¡microbe n. ΢ÉúÎï,ϸ¾ú