# Current Challenges in _Yersinia_ Diagnosis and Treatment
## 7 _Yersinia_ Transmission
The variability of the LPS structure used by Gram-negative bacteria promotes survival, providing resistance to innate immune system components and preventing recognition by TLR4 [97]. LPS's lipid moiety, called lipid A, is localized in the membrane and serves as an anchor for the rest of the LPS molecule. LPS in the S (smooth) form consists of an external repeating glycan region called the O-specific polysaccharide (OPS), which is often called the O-antigen [8]. The OPS defines the bacteria's seropositive and protects bacteria from host defense mechanisms (phagocytosis and complement-mediated killing) [97]. _Y. enterocolitic_ O:3 (YeO3) is considered the most common arthitogenic agent that can cause reactive arthritis (ReA) [98]. Bacteria may gain access to blood circulation, grow in the Peyer's tissue, and be transferred to the joint via plasma or within lymphatic cells [99]. As a result, _Yersinia_ infection can cause reactive arthritis, which is associated with the synthesis of specific antibodies. Unfortunately, some cellular components, such as LPS or endotoxin, persist in the joint (even after bacterial elimination), and they initiate the clinical symptoms [97]. Therefore, the _Yersinia_ antigens (including LPS) are detected in synovial fluid cells [99]. In addition to LPS, the complement system is also detected in synovial fluids and plays a significant role in the induction of _Yersinia_ inflammation [100]. Interestingly, complement inhibition is associated with a less severe form of the disease [101]. For example, mice deficient in complement components were found to be resistant to arthritis [100]. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline \multicolumn{1}{c}{**General Characteristics**} & **Crucial Yop Function** & **Mechanism** & \multicolumn{1}{c}{**Therapeutic Use of the Recombinant Form**} \\ \hline \hline YopM & & & & Involved in the treatment of auto-inflammatory diseases, e.g., induce platelet aggregation. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Characteristics of the _Yersinia_ outer proteins (Yops) and their possible use in clinical practice. \begin{table}
\begin{tabular}{l l l l} \hline \hline \multicolumn{1}{c}{**General Characteristics**} & \multicolumn{1}{c}{**Crucial Yop Function**} & \multicolumn{1}{c}{**Mechanism**} & \multicolumn{1}{c}{**Therapeutic Use of the Recombinant Form**} \\ \hline \hline \multicolumn{1}{c}{YopE} & & & \\ \(\bullet\) & A GTPase-activating protein for Rac1 & & & \\  & and RhoA; & & & \\  & Inhibits the activities of RhoA, Rac1, & & & \\  & and Cdc42 (the small GTPase signaling molecules) [110]; & & & \\  & Diminishes phagocytosis and Yop & & & \\  & translocation; & & & \\  & Inhibits IL-8 synthesis, which is an & & & \\  & important chemoattractant and & & \\  & activator for neutrophils [111]; & & & \\  & defense against & & \\  & \(\downarrow\) IL-1\(\beta\) maturation [112]; & & & \\  & phagocytes [114]. & & & \\  & macrophages—pre-requisite cells & & & \\  & during splenic colonization by & & \\  & _Yersinia_[110]; & & & \\  & \(\downarrow\) neutrophil migration, which mainly & & & \\  & depends on Rho-mediated & & \\  & signaling [113]. & & & \\ \hline \multicolumn{1}{c}{YopT} & & & \\  &