Emergency Medical Technician (EMT) Intermediate Practice Exam

A biphasic response to an antigen occurs when?

1. An acute response is followed later by a delayed response

2. A second acute response occurs immediately after the first

3. The body fails to respond to the antigen

4. An allergic reaction is triggered

The correct answer is: An acute response is followed later by a delayed response

A biphasic response to an antigen is characterized by an initial acute immune response that is followed by a subsequent, often delayed response. This can occur in various immunological scenarios, particularly in the context of allergic reactions or certain infections where the immune system first responds vigorously to an antigen, then, after a brief period of resolution, mounts another response. In the case of allergies, for example, an individual may first experience symptoms shortly after exposure to an allergen due to the immediate release of mediators like histamine. After a interval, there may be a secondary release of various substances leading to a recurrence of symptoms, representing the delayed phase of the response. This biphasic nature highlights the complexity of the immune response and illustrates how the body can recognize and react to the same antigen at multiple points in time. The other options do not accurately describe the biphasic response: a second acute response immediately after the first does not imply the delayed nature of the response; failure to respond does not represent a biphasic reaction; and while an allergic reaction may involve a biphasic response, it does not fully encompass the definition since biphasic responses can occur in other scenarios beyond just allergies.