The pathological study showed that the primary infection was a kind of reaction to foreign body, while that of the re - infection was allergic.

病理学研究显示，初次感染以异物反应为特征，再次感染以过敏反应为特征。

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The body produces an inflammatory reaction in response to foreign invaders, such as pollutants.

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Another theory is that the initial illness may have created an autoimmune reaction, causing the body's immune system to attack normal cells as if they were foreign substances.

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