The animal study proved that the supplement of vitamin D could significantly increase the ratios of CD4+/CD8+ in mice.[38] Therefore, vitamin D deficiency may result in decreased CD4+/CD8+, reducing the ability of the host to prevent an exaggerated immune response to pathogenic microorganisms that may negatively impact host’s immune function and cause the progression of periodontitis. The gene discussed is CD4; the disease is vitamin D deficiency.