Therefore, we hypothesized that in secondary syphilis infection patients, ICOS+Tfh or effector memory Tfh cells help B cells produce the neutralizing antibody to fight against syphilis, but in latent syphilis patients, these Tfh subsets do not activate the B cells to increase the production of neutralizing antibodies needed to eliminate syphilis from the human body. This evidence concerns the gene ICOS and latent syphilis.