The statements below are made about some animal pathogens that may evade innate and inflammatory responses by the following mechanisms:

A. The flagellin of Proteobacteria has a mutation that prevents it from being recognized by Toll-like receptors (TLRs).
B. The lipopolysaccharides of Helicobacter have mutations that prevent it from being recognized by TLRs.
C. M. tuberculosis escapes from the phagosome to the cytosol, thereby avoiding degradation by lysosomal enzymes.
D. Influenza virus produces Yop protein that inhibits inflammasome activity.
E. S. typhi encodes a protein that binds Type I IFNs and prevents them from binding to the IFN receptor.

Which one of the following options represents the combination of all correct statements?

Correct option is D

Explanation:

Statement A: Flagellin mutation in Proteobacteria prevents recognition by TLRs - Correct

• Flagellin is the structural protein of bacterial flagella.
  It is recognized by TLR5, a pattern recognition receptor on host immune cells, triggering innate immune responses.

• Immune Evasion:
  Some Proteobacteria have evolved mutations in flagellin that reduce or prevent its recognition by TLR5.
  This allows them to avoid activating innate immunity, helping in immune evasion and persistence.

Statement B: LPS mutations in Helicobacter prevent TLR recognition- Correct

• Lipopolysaccharide (LPS) is a key component of the outer membrane of Gram-negative bacteria and is recognized by TLR4.

• Immune Evasion:
  Helicobacter pylori modifies its LPS structure (e.g., altered lipid A) to reduce TLR4 recognition.
  This dampens immune activation and allows it to persist in the harsh gastric environment.

Statement C: M. tuberculosis escapes phagosome to cytosol -Incorrect

• M. tuberculosis is an intracellular pathogen that infects macrophages.

• Immune Evasion:
  Instead of escaping to the cytosol, M. tuberculosisprevents phagosome-lysosome fusion, allowing it to survive inside the phagosome.
  Cytosolic escape is more typical of bacteria like Listeria monocytogenes.

Statement D: Influenza virus produces Yop protein - Incorrect

• Yop proteins are secreted by Yersinia species via Type III secretion system to inhibit inflammasomes and immune signaling.

• Influenza Virus:
  Influenza virus does not produce Yop proteins. It uses other mechanisms (e.g., NS1 protein) to evade immune responses.

Statement E: S. typhi protein binds Type I IFNs - Incorrect

• Salmonella typhi evades host immunity through multiple mechanisms, including interference with cytokine signaling.

• Protein binding Type I IFNs:
  While S. typhi modulates immune signaling, specific binding of Type I IFNs to prevent receptor binding is not a well-characterized or widely accepted mechanism for this pathogen.