LAP3 and infection: Recent studies revealed that two-component signaling systems of bacteria could sense the biochemical signals in environment of hosts and then upregulate the synthesis and excretion levels of target proteins against the adverse conditions for survival.58 The data indicate that the infection of host cells acts as a stimulus to cause the increase of denatured proteins in L. interrogans and the leptospiral HslUV chaperone–peptidase complex may have a special role in maintaining the ability of the spirochete to sense and respond to the infectious environment.