2. 考研
  3. The immune system is equal in complexity to the combined intricacies of the brain and nervous system. The success of the immune

The immune system is equal in complexity to the combined intricacies of the brain and nervous system. The success of the immune

admin2019-08-01  42
问题     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 and 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.
    At 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 or 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, immune cells and other body cells coexist peaceably in a state known as self-tolerance. When a normally functioning immune system attacks a non-self molecule, the system has the ability to remember the specifics of the foreign body. Upon subsequent encounters with the same species of molecules, 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 non-self 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 self-markers) 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, non-antigenic building blocks. An antigen announces its foreignness by means of intricate and characteristic shapes called epitopes, which stick out from its surface. Most antigens, even the simplest microbes, carry several different kinds of epitopes on their surface, some may even carry several hundred. Some epitopes 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 these diseases are caused by a person’s immune system actually attacking itself.
The remembering power of a person’s immune system is______.
选项 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
答案C
解析 细节题。第二段第六句以下内容谈到ability to remember(记忆能力)。第八句明确指出，除哺乳期内可能传递部分抗体外，其他记忆能力需免疫系统自身学习获得，第九句举例说明这一现象，[A]中的is descended(是遗传下来的)与第八句的is not inherited(不是遗传而得的)相矛盾；[B]中的passed down与[A]相同；[D]说法中文中并无依据。只有[C]与第九句意思相符，为正确选项。
转载请注明原文地址:https://kaotiyun.com/show/hI2Z777K
0

考研英语一

相关试题推荐
随机试题
最新回复(0)