The diphtheria toxin has an affinity for all the following tissues EXCEPT
**Question:** The diphtheria toxin has an affinity for all the following tissues EXCEPT
A. Cardiac muscle
B. Nerve fibers
C. Kidney
D. Liver
**Core Concept:**
Diphtheria is a bacterial infection caused by the bacterium Corynebacterium diphtheriae. The toxin produced by this bacterium is responsible for the characteristic lesions and systemic effects of the disease. The diphtheria toxin exhibits high affinity for some tissues, which is why it is essential to understand which ones it does not bind to.
**Why the Correct Answer is Right:**
The correct answer "D. Liver" is right because diphtheria toxin primarily binds to and affects cardiac muscle (A), nerve fibers (B), and kidney (C). The liver is not a primary target of the toxin. Diphtheria toxin is known to interfere with protein synthesis in the cell by inhibiting the enzyme ADP ribosylase, which affects cardiac muscle contractions and nerve functions. It also damages kidney tissue, but the primary effects are seen in cardiac muscle and nerves.
**Why Each Wrong Option is Incorrect:**
A. Cardiac muscle (Correct) - Diphtheria toxin is involved in the inhibition of protein synthesis in cardiac muscle cells, leading to muscle weakness and paralysis.
B. Nerve fibers (Correct) - Diphtheria toxin targets and damages the peripheral and autonomic neurons, causing paralysis and respiratory failure.
C. Kidney (Incorrect) - Although diphtheria toxin does cause kidney damage, the primary effects are seen in cardiac muscle and nerves.
D. Liver (Incorrect) - As explained above, the liver is not a primary target of the toxin. Diphtheria toxin primarily affects cardiac muscle, nerves, and kidney tissues.
**Clinical Pearl:**
Understanding the specific target tissues of diphtheria toxin is vital for proper diagnosis and management of diphtheria. The toxin affects cardiac muscle, nerves, and kidney, whereas the liver is not the primary site of action. This knowledge helps differentiate diphtheria from other conditions with similar symptoms and aids in appropriate treatment strategies.