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The immune system includes specialized white blood cells, called lymphocytes that adapt themselves to fight specific foreign invaders. These cells develop into two groups in the bone marrow.

From the bone marrow, one group of lymphocytes migrates to a gland called the thymus and become T lymphocytes or T cells. Within the thymus, the T cells mature under the influence of several hormones.

The T cells mature into several different types, including helper, killer and suppressor cells. T cells are responsible for cell-mediated immunity. This type of immunity becomes deficient in persons with HIV, the virus that causes AIDS, because HIV attacks and destroys helper T cells.

The other group of lymphocytes, B lymphocytes or B cells, mature and develop within the bone marrow itself. In that process, they achieve the ability to recognize specific foreign invaders. From the bone marrow, B cells migrate through the body fluids to the lymph nodes, spleen and blood. B lymphocytes provide the body with humoral immunity as they circulate in the fluids in search of specific foreign invaders to destroy.

重點詞匯匯總：

 lymphocyte/?l?mf?sa?t/n. [免疫] 淋巴細胞；淋巴球

 gland  /ɡl?nd/n. 腺密封壓蓋

thymus /?θa?m?s/n. 胸腺

suppressor cells抑制細胞 /s??pres?r/

n. 抑制器；消除器；消音器

cell-mediated immunity /sel,mi:dieitid/[免疫] 細胞免疫；[免疫] 細胞介導免疫

 lymph node淋巴結

spleen/spli?n/n. 脾臟；壞脾氣；怒氣

 humoral immunity 體液免疫 /'hj?m?r?l/adj. 體液的；溫性的；由體液引起的

百度翻譯：

免疫系統(tǒng)包括專門的白細胞，稱為淋巴細胞，適應特定的外來入侵者。這些細胞在骨髓中發(fā)育成兩組。

從骨髓中，一組淋巴細胞遷移到稱為胸腺的腺體，成為T淋巴細胞或T細胞。在胸腺內(nèi)，T細胞在幾種激素的影響下成熟。

T細胞成熟為幾種不同類型，包括輔助細胞，殺傷細胞和抑制細胞。T細胞負責細胞介導的免疫。由于艾滋病毒攻擊并破壞輔助性T細胞，這種免疫力在艾滋病病毒感染者中變得不足。

另一組淋巴細胞，B淋巴細胞或B細胞在骨髓本身內(nèi)成熟并發(fā)育。在這個過程中，他們實現(xiàn)了識別特定外國入侵者的能力。從骨髓中，B細胞通過體液遷移到淋巴結，脾臟和血液。B淋巴細胞為身體提供體液免疫，因為它們在液體中循環(huán)以尋找特定的外來入侵者來摧毀。