Aa Leukotoxin — MFDS Part 1 MCQ

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HardMicrobiologyAa LeukotoxinMFDS Part 1

An Aggregatibacter actinomycetemcomitans isolate from a patient with rapidly progressing periodontitis expresses a large RTX-family protein. Its cytotoxic effect on human neutrophils is inhibited by blocking the β2-integrin LFA-1 (CD11a/CD18). Which virulence factor is responsible?

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Correct answer: E — Leukotoxin A (LtxA)

Leukotoxin A (LtxA) is the characteristic leukocyte-targeting RTX-family toxin of A. actinomycetemcomitans. It interacts with LFA-1 (CD11a/CD18) on human leukocytes and can activate, injure and lyse neutrophils, thereby impairing local host defence. Cytolethal distending toxin is also produced by some strains, but acts principally through DNA damage and cell-cycle arrest rather than LFA-1-dependent neutrophil lysis. LPS activates innate inflammatory pathways but is not the selective RTX leukotoxin. EmaA is a collagen-binding adhesin, while the Flp fimbrial apparatus contributes to adherence, aggregation and biofilm formation. Therefore, the described virulence factor is LtxA.

Reference: Johansson A. Aggregatibacter actinomycetemcomitans leukotoxin: a powerful tool with capacity to cause imbalance in the host inflammatory response. Toxins. 2011;3(3):242–259. https://pubmed.ncbi.nlm.nih.gov/22069708/