CD28 and periodontitis: In terms of relative cell count, an increase in IgD + CD24 + B cell %lymphocyte (OR = 0.90 [0.82,0.99], P = 0.026), TCRgd T cell %lymphocyte (OR = 0.96 [0.93,0.99], P = 0.018), and CD45RA- CD28- CD8 + T cell %CD8 + T cell (OR = 0.9989 [0.9980,0.9998], P = 0.020) was associated with a decreased incidence of chronic periodontitis.