How do non-typhoidal Salmonella evade the immune system's recognition of their flagella?

Non-typhoidal Salmonella (NTS) have developed several strategies to evade the immune system's recognition of their flagella, which are key structures for their motility and pathogenicity. Here are the steps explaining how they do this:

1. Phase Variation: NTS can switch between two different types of flagellar proteins, known as H1 and H2. This process, known as phase variation, can help the bacteria evade the host's immune response. When the immune system starts recognizing and attacking one type of flagellar protein, the bacteria can switch to the other type.

2. Masking of Flagella: NTS can also hide their flagella from the immune system. They do this by expressing a specific protein called FliS that binds to the flagellin (the protein that makes up the flagella) and prevents its recognition by the immune system.

3. Suppression of Flagella Expression: NTS can suppress the expression of their flagella when they are inside host cells. This helps them avoid detection by the host's immune system.

4. Biofilm Formation: NTS can form biofilms, which are communities of bacteria that are protected by a matrix of extracellular polymeric substances. This matrix can help shield the bacteria's flagella from the immune system.

5. Induction of Tolerance: NTS can induce a state of tolerance in the host's immune system. This means that the immune system becomes less responsive to the presence of the bacteria's flagella, allowing the bacteria to evade detection.

These strategies allow NTS to survive and proliferate within the host, leading to persistent infections.