CD28 and periodontitis: Although the presence and activity of CD4+CD28- T lymphocytes during periodontitis, the most prevalent osteolytic disease in humans, has not been reported, the continuous inflammatory signals and the persistent antigenic stimulus, provided by microbial dysbiosis and the destruction of periodontal tissues, could trigger the loss of CD28 expression and senescence of CD4+ T lymphocytes [74, 75].